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| author | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
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| committer | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
| commit | 4bfd864f10b68b71482b35c818559068ef8d5797 (patch) | |
| tree | e3989f47a7994642eb325063d46e8f08ffa681dc /doc/rfc/rfc9012.txt | |
| parent | ea76e11061bda059ae9f9ad130a9895cc85607db (diff) | |
doc: Add RFC documents
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diff --git a/doc/rfc/rfc9012.txt b/doc/rfc/rfc9012.txt new file mode 100644 index 0000000..493cb59 --- /dev/null +++ b/doc/rfc/rfc9012.txt @@ -0,0 +1,2271 @@ + + + + +Internet Engineering Task Force (IETF) K. Patel +Request for Comments: 9012 Arrcus, Inc +Obsoletes: 5512, 5566 G. Van de Velde +Updates: 5640 Nokia +Category: Standards Track S. Sangli +ISSN: 2070-1721 J. Scudder + Juniper Networks + April 2021 + + + The BGP Tunnel Encapsulation Attribute + +Abstract + + This document defines a BGP path attribute known as the "Tunnel + Encapsulation attribute", which can be used with BGP UPDATEs of + various Subsequent Address Family Identifiers (SAFIs) to provide + information needed to create tunnels and their corresponding + encapsulation headers. It provides encodings for a number of tunnel + types, along with procedures for choosing between alternate tunnels + and routing packets into tunnels. + + This document obsoletes RFC 5512, which provided an earlier + definition of the Tunnel Encapsulation attribute. RFC 5512 was never + deployed in production. Since RFC 5566 relies on RFC 5512, it is + likewise obsoleted. This document updates RFC 5640 by indicating + that the Load-Balancing Block sub-TLV may be included in any Tunnel + Encapsulation attribute where load balancing is desired. + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 7841. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + https://www.rfc-editor.org/info/rfc9012. + +Copyright Notice + + Copyright (c) 2021 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (https://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + +Table of Contents + + 1. Introduction + 1.1. Brief Summary of RFC 5512 + 1.2. Deficiencies in RFC 5512 + 1.3. Use Case for the Tunnel Encapsulation Attribute + 1.4. Brief Summary of Changes from RFC 5512 + 1.5. Update to RFC 5640 + 1.6. Effects of Obsoleting RFC 5566 + 2. The Tunnel Encapsulation Attribute + 3. Tunnel Encapsulation Attribute Sub-TLVs + 3.1. The Tunnel Egress Endpoint Sub-TLV (Type Code 6) + 3.1.1. Validating the Address Subfield + 3.2. Encapsulation Sub-TLVs for Particular Tunnel Types (Type + Code 1) + 3.2.1. VXLAN (Tunnel Type 8) + 3.2.2. NVGRE (Tunnel Type 9) + 3.2.3. L2TPv3 (Tunnel Type 1) + 3.2.4. GRE (Tunnel Type 2) + 3.2.5. MPLS-in-GRE (Tunnel Type 11) + 3.3. Outer Encapsulation Sub-TLVs + 3.3.1. DS Field (Type Code 7) + 3.3.2. UDP Destination Port (Type Code 8) + 3.4. Sub-TLVs for Aiding Tunnel Selection + 3.4.1. Protocol Type Sub-TLV (Type Code 2) + 3.4.2. Color Sub-TLV (Type Code 4) + 3.5. Embedded Label Handling Sub-TLV (Type Code 9) + 3.6. MPLS Label Stack Sub-TLV (Type Code 10) + 3.7. Prefix-SID Sub-TLV (Type Code 11) + 4. Extended Communities Related to the Tunnel Encapsulation + Attribute + 4.1. Encapsulation Extended Community + 4.2. Router's MAC Extended Community + 4.3. Color Extended Community + 5. Special Considerations for IP-in-IP Tunnels + 6. Semantics and Usage of the Tunnel Encapsulation Attribute + 7. Routing Considerations + 7.1. Impact on the BGP Decision Process + 7.2. Looping, Mutual Recursion, Etc. + 8. Recursive Next-Hop Resolution + 9. Use of Virtual Network Identifiers and Embedded Labels When + Imposing a Tunnel Encapsulation + 9.1. Tunnel Types without a Virtual Network Identifier Field + 9.2. Tunnel Types with a Virtual Network Identifier Field + 9.2.1. Unlabeled Address Families + 9.2.2. Labeled Address Families + 10. Applicability Restrictions + 11. Scoping + 12. Operational Considerations + 13. Validation and Error Handling + 14. IANA Considerations + 14.1. Obsoleting RFC 5512 + 14.2. Obsoleting Code Points Assigned by RFC 5566 + 14.3. Border Gateway Protocol (BGP) Tunnel Encapsulation + Grouping + 14.4. BGP Tunnel Encapsulation Attribute Tunnel Types + 14.5. Subsequent Address Family Identifiers + 14.6. BGP Tunnel Encapsulation Attribute Sub-TLVs + 14.7. Flags Field of VXLAN Encapsulation Sub-TLV + 14.8. Flags Field of NVGRE Encapsulation Sub-TLV + 14.9. Embedded Label Handling Sub-TLV + 14.10. Color Extended Community Flags + 15. Security Considerations + 16. References + 16.1. Normative References + 16.2. Informative References + Appendix A. Impact on RFC 8365 + Acknowledgments + Contributors + Authors' Addresses + +1. Introduction + + This document obsoletes [RFC5512]. The deficiencies of [RFC5512], + and a summary of the changes made, are discussed in Sections 1.1-1.3. + The material from [RFC5512] that is retained has been incorporated + into this document. Since [RFC5566] relies on [RFC5512], it is + likewise obsoleted. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and + "OPTIONAL" in this document are to be interpreted as described in + BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all + capitals, as shown here. + +1.1. Brief Summary of RFC 5512 + + [RFC5512] defines a BGP path attribute known as the Tunnel + Encapsulation attribute. This attribute consists of one or more + TLVs. Each TLV identifies a particular type of tunnel. Each TLV + also contains one or more sub-TLVs. Some of the sub-TLVs, for + example, the Encapsulation sub-TLV, contain information that may be + used to form the encapsulation header for the specified tunnel type. + Other sub-TLVs, for example, the "color sub-TLV" and the "protocol + sub-TLV", contain information that aids in determining whether + particular packets should be sent through the tunnel that the TLV + identifies. + + [RFC5512] only allows the Tunnel Encapsulation attribute to be + attached to BGP UPDATE messages of the Encapsulation Address Family. + These UPDATE messages have an Address Family Identifier (AFI) of 1 or + 2, and a SAFI of 7. In an UPDATE of the Encapsulation SAFI, the + Network Layer Reachability Information (NLRI) is an address of the + BGP speaker originating the UPDATE. Consider the following scenario: + + * BGP speaker R1 has received and selected UPDATE U for local use; + + * UPDATE U's SAFI is the Encapsulation SAFI; + + * UPDATE U has the address R2 as its NLRI; + + * UPDATE U has a Tunnel Encapsulation attribute. + + * R1 has a packet, P, to transmit to destination D; and + + * R1's best route to D is a BGP route that has R2 as its next hop. + + In this scenario, when R1 transmits packet P, it should transmit it + to R2 through one of the tunnels specified in U's Tunnel + Encapsulation attribute. The IP address of the tunnel egress + endpoint of each such tunnel is R2. Packet P is known as the + tunnel's "payload". + +1.2. Deficiencies in RFC 5512 + + While the ability to specify tunnel information in a BGP UPDATE is + useful, the procedures of [RFC5512] have certain limitations: + + * The requirement to use the Encapsulation SAFI presents an + unfortunate operational cost, as each BGP session that may need to + carry tunnel encapsulation information needs to be reconfigured to + support the Encapsulation SAFI. The Encapsulation SAFI has never + been used, and this requirement has served only to discourage the + use of the Tunnel Encapsulation attribute. + + * There is no way to use the Tunnel Encapsulation attribute to + specify the tunnel egress endpoint address of a given tunnel; + [RFC5512] assumes that the tunnel egress endpoint of each tunnel + is specified as the NLRI of an UPDATE of the Encapsulation SAFI. + + * If the respective best routes to two different address prefixes + have the same next hop, [RFC5512] does not provide a + straightforward method to associate each prefix with a different + tunnel. + + * If a particular tunnel type requires an outer IP or UDP + encapsulation, there is no way to signal the values of any of the + fields of the outer encapsulation. + + * In the specification of the sub-TLVs in [RFC5512], each sub-TLV + has a one-octet Length field. In some cases, where a sub-TLV may + require more than 255 octets for its encoding, a two-octet Length + field may be needed. + +1.3. Use Case for the Tunnel Encapsulation Attribute + + Consider the case of a router R1 forwarding an IP packet P. Let D be + P's IP destination address. R1 must look up D in its forwarding + table. Suppose that the "best match" route for D is route Q, where Q + is a BGP-distributed route whose "BGP next hop" is router R2. And + suppose further that the routers along the path from R1 to R2 have + entries for R2 in their forwarding tables but do NOT have entries for + D in their forwarding tables. For example, the path from R1 to R2 + may be part of a "BGP-free core", where there are no BGP-distributed + routes at all in the core. Or, as in [RFC5565], D may be an IPv4 + address while the intermediate routers along the path from R1 to R2 + may support only IPv6. + + In cases such as this, in order for R1 to properly forward packet P, + it must encapsulate P and send P "through a tunnel" to R2. For + example, R1 may encapsulate P using GRE, Layer 2 Tunneling Protocol + version 3 (L2TPv3), IP in IP, etc., where the destination IP address + of the encapsulation header is the address of R2. + + In order for R1 to encapsulate P for transport to R2, R1 must know + what encapsulation protocol to use for transporting different sorts + of packets to R2. R1 must also know how to fill in the various + fields of the encapsulation header. With certain encapsulation + types, this knowledge may be acquired by default or through manual + configuration. Other encapsulation protocols have fields such as + session id, key, or cookie that must be filled in. It would not be + desirable to require every BGP speaker to be manually configured with + the encapsulation information for every one of its BGP next hops. + + This document specifies a way in which BGP itself can be used by a + given BGP speaker to tell other BGP speakers, "If you need to + encapsulate packets to be sent to me, here's the information you need + to properly form the encapsulation header". A BGP speaker signals + this information to other BGP speakers by using a new BGP attribute + type value -- the BGP Tunnel Encapsulation attribute. This attribute + specifies the encapsulation protocols that may be used, as well as + whatever additional information (if any) is needed in order to + properly use those protocols. Other attributes, for example, + communities or extended communities, may also be included. + +1.4. Brief Summary of Changes from RFC 5512 + + This document addresses the deficiencies identified in Section 1.2 + by: + + * Deprecating the Encapsulation SAFI. + + * Defining a new "Tunnel Egress Endpoint sub-TLV" (Section 3.1) that + can be included in any of the TLVs contained in the Tunnel + Encapsulation attribute. This sub-TLV can be used to specify the + remote endpoint address of a particular tunnel. + + * Allowing the Tunnel Encapsulation attribute to be carried by BGP + UPDATEs of additional AFI/SAFIs. Appropriate semantics are + provided for this way of using the attribute. + + * Defining a number of new sub-TLVs that provide additional + information that is useful when forming the encapsulation header + used to send a packet through a particular tunnel. + + * Defining the Sub-TLV Type field so that a sub-TLV whose type is in + the range from 0 to 127 (inclusive) has a one-octet Length field, + but a sub-TLV whose type is in the range from 128 to 255 + (inclusive) has a two-octet Length field. + + One of the sub-TLVs defined in [RFC5512] is the "Encapsulation sub- + TLV". For a given tunnel, the Encapsulation sub-TLV specifies some + of the information needed to construct the encapsulation header used + when sending packets through that tunnel. This document defines + Encapsulation sub-TLVs for a number of tunnel types not discussed in + [RFC5512]: Virtual eXtensible Local Area Network (VXLAN) [RFC7348], + Network Virtualization Using Generic Routing Encapsulation (NVGRE) + [RFC7637], and MPLS in Generic Routing Encapsulation (MPLS-in-GRE) + [RFC4023]. MPLS-in-UDP [RFC7510] is also supported, but an + Encapsulation sub-TLV for it is not needed since there are no + additional parameters to be signaled. + + Some of the encapsulations mentioned in the previous paragraph need + to be further encapsulated inside UDP and/or IP. [RFC5512] provides + no way to specify that certain information is to appear in these + outer IP and/or UDP encapsulations. This document provides a + framework for including such information in the TLVs of the Tunnel + Encapsulation attribute. + + When the Tunnel Encapsulation attribute is attached to a BGP UPDATE + whose AFI/SAFI identifies one of the labeled address families, it is + not always obvious whether the label embedded in the NLRI is to + appear somewhere in the tunnel encapsulation header (and if so, + where), whether it is to appear in the payload, or whether it can be + omitted altogether. This is especially true if the tunnel + encapsulation header itself contains a "virtual network identifier". + This document provides a mechanism that allows one to signal (by + using sub-TLVs of the Tunnel Encapsulation attribute) how one wants + to use the embedded label when the tunnel encapsulation has its own + Virtual Network Identifier field. + + [RFC5512] defines an Encapsulation Extended Community that can be + used instead of the Tunnel Encapsulation attribute under certain + circumstances. This document describes how the Encapsulation + Extended Community can be used in a backwards-compatible fashion (see + Section 4.1). It is possible to combine Encapsulation Extended + Communities and Tunnel Encapsulation attributes in the same BGP + UPDATE in this manner. + +1.5. Update to RFC 5640 + + This document updates [RFC5640] by indicating that the Load-Balancing + Block sub-TLV MAY be included in any Tunnel Encapsulation attribute + where load balancing is desired. + +1.6. Effects of Obsoleting RFC 5566 + + This specification obsoletes RFC 5566. This has the effect of, in + turn, deprecating a number of code points defined in that document. + In the "BGP Tunnel Encapsulation Attribute Tunnel Types" registry + [IANA-BGP-TUNNEL-ENCAP], the following code points have been marked + as deprecated: "Transmit tunnel endpoint" (type code 3), "IPsec in + Tunnel-mode" (type code 4), "IP in IP tunnel with IPsec Transport + Mode" (type code 5), and "MPLS-in-IP tunnel with IPsec Transport + Mode" (type code 6). In the "BGP Tunnel Encapsulation Attribute Sub- + TLVs" registry [IANA-BGP-TUNNEL-ENCAP], "IPsec Tunnel Authenticator" + (type code 3) has been marked as deprecated. See Section 14.2. + +2. The Tunnel Encapsulation Attribute + + The Tunnel Encapsulation attribute is an optional transitive BGP path + attribute. IANA has assigned the value 23 as the type code of the + attribute in the "BGP Path Attributes" registry [IANA-BGP-PARAMS]. + The attribute is composed of a set of Type-Length-Value (TLV) + encodings. Each TLV contains information corresponding to a + particular tunnel type. A Tunnel Encapsulation TLV, also known as + Tunnel TLV, is structured as shown in Figure 1. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Tunnel Type (2 octets) | Length (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Value (variable) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 1: Tunnel Encapsulation TLV + + Tunnel Type (2 octets): Identifies a type of tunnel. The field + contains values from the IANA registry "BGP Tunnel Encapsulation + Attribute Tunnel Types" [IANA-BGP-TUNNEL-ENCAP]. See + Section 3.4.1 for discussion of special treatment of tunnel types + with names of the form "X-in-Y". + + Length (2 octets): The total number of octets of the Value field. + + Value (variable): Comprised of multiple sub-TLVs. + + Each sub-TLV consists of three fields: A 1-octet type, a 1-octet or + 2-octet length (depending on the type), and zero or more octets of + value. A sub-TLV is structured as shown in Figure 2. + + +--------------------------------+ + | Sub-TLV Type (1 octet) | + +--------------------------------+ + | Sub-TLV Length (1 or 2 octets) | + +--------------------------------+ + | Sub-TLV Value (variable) | + +--------------------------------+ + + Figure 2: Encapsulation Sub-TLV + + Sub-TLV Type (1 octet): Each sub-TLV type defines a certain property + about the Tunnel TLV that contains this sub-TLV. The field + contains values from the IANA registry "BGP Tunnel Encapsulation + Attribute Sub-TLVs" [IANA-BGP-TUNNEL-ENCAP]. + + Sub-TLV Length (1 or 2 octets): The total number of octets of the + Sub-TLV Value field. The Sub-TLV Length field contains 1 octet if + the Sub-TLV Type field contains a value in the range from 0-127. + The Sub-TLV Length field contains two octets if the Sub-TLV Type + field contains a value in the range from 128-255. + + Sub-TLV Value (variable): Encodings of the Value field depend on the + sub-TLV type. The following subsections define the encoding in + detail. + +3. Tunnel Encapsulation Attribute Sub-TLVs + + This section specifies a number of sub-TLVs. These sub-TLVs can be + included in a TLV of the Tunnel Encapsulation attribute. + +3.1. The Tunnel Egress Endpoint Sub-TLV (Type Code 6) + + The Tunnel Egress Endpoint sub-TLV specifies the address of the + egress endpoint of the tunnel, that is, the address of the router + that will decapsulate the payload. Its Value field contains three + subfields: + + 1. a Reserved subfield + + 2. a two-octet Address Family subfield + + 3. an Address subfield, whose length depends upon the Address + Family. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Reserved (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Address Family (2 octets) | Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable) + + ~ ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 3: Tunnel Egress Endpoint Sub-TLV Value Field + + The Reserved subfield SHOULD be originated as zero. It MUST be + disregarded on receipt, and it MUST be propagated unchanged. + + The Address Family subfield contains a value from IANA's "Address + Family Numbers" registry [IANA-ADDRESS-FAM]. This document assumes + that the Address Family is either IPv4 or IPv6; use of other address + families is outside the scope of this document. + + If the Address Family subfield contains the value for IPv4, the + Address subfield MUST contain an IPv4 address (a /32 IPv4 prefix). + + If the Address Family subfield contains the value for IPv6, the + Address subfield MUST contain an IPv6 address (a /128 IPv6 prefix). + + In a given BGP UPDATE, the address family (IPv4 or IPv6) of a Tunnel + Egress Endpoint sub-TLV is independent of the address family of the + UPDATE itself. For example, an UPDATE whose NLRI is an IPv4 address + may have a Tunnel Encapsulation attribute containing Tunnel Egress + Endpoint sub-TLVs that contain IPv6 addresses. Also, different + tunnels represented in the Tunnel Encapsulation attribute may have + tunnel egress endpoints of different address families. + + There is one special case: the Tunnel Egress Endpoint sub-TLV MAY + have a Value field whose Address Family subfield contains 0. This + means that the tunnel's egress endpoint is the address of the next + hop. If the Address Family subfield contains 0, the Address subfield + is omitted. In this case, the Length field of Tunnel Egress Endpoint + sub-TLV MUST contain the value 6 (0x06). + + When the Tunnel Encapsulation attribute is carried in an UPDATE + message of one of the AFI/SAFIs specified in this document (see the + first paragraph of Section 6), each TLV MUST have one, and only one, + Tunnel Egress Endpoint sub-TLV. If a TLV does not have a Tunnel + Egress Endpoint sub-TLV, that TLV should be treated as if it had a + malformed Tunnel Egress Endpoint sub-TLV (see below). + + In the context of this specification, if the Address Family subfield + has any value other than IPv4, IPv6, or the special value 0, the + Tunnel Egress Endpoint sub-TLV is considered "unrecognized" (see + Section 13). If any of the following conditions hold, the Tunnel + Egress Endpoint sub-TLV is considered to be "malformed": + + * The length of the sub-TLV's Value field is other than 6 added to + the defined length for the address family given in its Address + Family subfield. Therefore, for address family behaviors defined + in this document, the permitted values are: + + - 10, if the Address Family subfield contains the value for IPv4. + + - 22, if the Address Family subfield contains the value for IPv6. + + - 6, if the Address Family subfield contains the value zero. + + * The IP address in the sub-TLV's Address subfield lies within a + block listed in the relevant Special-Purpose IP Address registry + [RFC6890] with either a "destination" attribute value or a + "forwardable" attribute value of "false". (Such routes are + sometimes colloquially known as "Martians".) This restriction MAY + be relaxed by explicit configuration. + + * It can be determined that the IP address in the sub-TLV's Address + subfield does not belong to the Autonomous System (AS) that + originated the route that contains the attribute. Section 3.1.1 + describes an optional procedure to make this determination. + + Error handling is specified in Section 13. + + If the Tunnel Egress Endpoint sub-TLV contains an IPv4 or IPv6 + address that is valid but not reachable, the sub-TLV is not + considered to be malformed. + +3.1.1. Validating the Address Subfield + + This section provides a procedure that MAY be applied to validate + that the IP address in the sub-TLV's Address subfield belongs to the + AS that originated the route that contains the attribute. (The + notion of "belonging to" an AS is expanded on below.) Doing this is + thought to increase confidence that when traffic is sent to the IP + address depicted in the Address subfield, it will go to the same AS + as it would go to if the Tunnel Encapsulation attribute were not + present, although of course it cannot guarantee it. See Section 15 + for discussion of the limitations of this procedure. The principal + applicability of this procedure is in deployments that are not + strictly scoped. In deployments with strict scope, and especially + those scoped to a single AS, these procedures may not add substantial + benefit beyond those discussed in Section 11. + + The Route Origin Autonomous System Number (ASN) of a BGP route that + includes a Tunnel Encapsulation attribute can be determined by + inspection of the AS_PATH attribute, according to the procedure + specified in [RFC6811], Section 2. Call this value Route_AS. + + In order to determine the Route Origin ASN of the address depicted in + the Address subfield of the Tunnel Egress Endpoint sub-TLV, it is + necessary to consider the forwarding route -- that is, the route that + will be used to forward traffic toward that address. This route is + determined by a recursive route-lookup operation for that address, as + discussed in [RFC4271], Section 5.1.3. The relevant AS path to + consider is the last one encountered while performing the recursive + lookup; the procedures of [RFC6811], Section 2 are applied to that AS + path to determine the Route Origin ASN. If no AS path is encountered + at all, for example, if that route's source is a protocol other than + BGP, the Route Origin ASN is the BGP speaker's own AS number. Call + this value Egress_AS. + + If Route_AS does not equal Egress_AS, then the Tunnel Egress Endpoint + sub-TLV is considered not to be valid. In some cases, a network + operator who controls a set of ASes might wish to allow a tunnel + egress endpoint to reside in an AS other than Route_AS; configuration + MAY allow for such a case, in which case the check becomes: if + Egress_AS is not within the configured set of permitted AS numbers, + then the Tunnel Egress Endpoint sub-TLV is considered to be + "malformed". + + Note that if the forwarding route changes, this procedure MUST be + reapplied. As a result, a sub-TLV that was formerly considered valid + might become not valid, or vice versa. + +3.2. Encapsulation Sub-TLVs for Particular Tunnel Types (Type Code 1) + + This section defines Encapsulation sub-TLVs for the following tunnel + types: VXLAN [RFC7348], NVGRE [RFC7637], MPLS-in-GRE [RFC4023], + L2TPv3 [RFC3931], and GRE [RFC2784]. + + Rules for forming the encapsulation based on the information in a + given TLV are given in Sections 6 and 9. + + Recall that the tunnel type itself is identified by the Tunnel Type + field in the attribute header (Section 2); the Encapsulation sub- + TLV's structure is inferred from this. Regardless of the tunnel + type, the sub-TLV type of the Encapsulation sub-TLV is 1. There are + also tunnel types for which it is not necessary to define an + Encapsulation sub-TLV, because there are no fields in the + encapsulation header whose values need to be signaled from the tunnel + egress endpoint. + +3.2.1. VXLAN (Tunnel Type 8) + + This document defines an Encapsulation sub-TLV for VXLAN [RFC7348] + tunnels. When the tunnel type is VXLAN, the length of the sub-TLV is + 12 octets. The structure of the Value field in the Encapsulation + sub-TLV is shown in Figure 4. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |V|M|R|R|R|R|R|R| VN-ID (3 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MAC Address (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MAC Address (2 octets) | Reserved (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 4: VXLAN Encapsulation Sub-TLV Value Field + + V: This bit is set to 1 to indicate that a Virtual Network + Identifier (VN-ID) is present in the Encapsulation sub-TLV. If + set to 0, the VN-ID field is disregarded. Please see Section 9. + + M: This bit is set to 1 to indicate that a Media Access Control + (MAC) Address is present in the Encapsulation sub-TLV. If set to + 0, the MAC Address field is disregarded. + + R: The remaining bits in the 8-bit Flags field are reserved for + further use. They MUST always be set to 0 by the originator of + the sub-TLV. Intermediate routers MUST propagate them without + modification. Any receiving routers MUST ignore these bits upon + receipt. + + VN-ID: If the V bit is set to 1, the VN-ID field contains a 3-octet + VN-ID value. If the V bit is set to 0, the VN-ID field MUST be + set to zero on transmission and disregarded on receipt. + + MAC Address: If the M bit is set to 1, this field contains a 6-octet + Ethernet MAC address. If the M bit is set to 0, this field MUST + be set to all zeroes on transmission and disregarded on receipt. + + Reserved: MUST be set to zero on transmission and disregarded on + receipt. + + When forming the VXLAN encapsulation header: + + * The values of the V, M, and R bits are NOT copied into the Flags + field of the VXLAN header. The Flags field of the VXLAN header is + set as per [RFC7348]. + + * If the M bit is set to 1, the MAC Address is copied into the Inner + Destination MAC Address field of the Inner Ethernet Header (see + Section 5 of [RFC7348]). + + If the M bit is set to 0, and the payload being sent through the + VXLAN tunnel is an Ethernet frame, the Destination MAC Address + field of the Inner Ethernet Header is just the Destination MAC + Address field of the payload's Ethernet header. + + If the M bit is set to 0, and the payload being sent through the + VXLAN tunnel is an IP or MPLS packet, the Inner Destination MAC + Address field is set to a configured value; if there is no + configured value, the VXLAN tunnel cannot be used. + + * If the V bit is set to 0, and the BGP UPDATE message has an AFI/ + SAFI other than Ethernet VPNs (SAFI 70, "BGP EVPNs"), then the + VXLAN tunnel cannot be used. + + * Section 9 describes how the VNI (VXLAN Network Identifier) field + of the VXLAN encapsulation header is set. + + Note that in order to send an IP packet or an MPLS packet through a + VXLAN tunnel, the packet must first be encapsulated in an Ethernet + header, which becomes the "Inner Ethernet Header" described in + [RFC7348]. The VXLAN Encapsulation sub-TLV may contain information + (for example, the MAC address) that is used to form this Ethernet + header. + +3.2.2. NVGRE (Tunnel Type 9) + + This document defines an Encapsulation sub-TLV for NVGRE [RFC7637] + tunnels. When the tunnel type is NVGRE, the length of the sub-TLV is + 12 octets. The structure of the Value field in the Encapsulation + sub-TLV is shown in Figure 5. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |V|M|R|R|R|R|R|R| VN-ID (3 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MAC Address (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | MAC Address (2 octets) | Reserved (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: NVGRE Encapsulation Sub-TLV Value Field + + V: This bit is set to 1 to indicate that a VN-ID is present in the + Encapsulation sub-TLV. If set to 0, the VN-ID field is + disregarded. Please see Section 9. + + M: This bit is set to 1 to indicate that a MAC Address is present in + the Encapsulation sub-TLV. If set to 0, the MAC Address field is + disregarded. + + R: The remaining bits in the 8-bit Flags field are reserved for + further use. They MUST always be set to 0 by the originator of + the sub-TLV. Intermediate routers MUST propagate them without + modification. Any receiving routers MUST ignore these bits upon + receipt. + + VN-ID: If the V bit is set to 1, the VN-ID field contains a 3-octet + VN-ID value, used to set the NVGRE Virtual Subnet Identifier + (VSID; see Section 9). If the V bit is set to 0, the VN-ID field + MUST be set to zero on transmission and disregarded on receipt. + + MAC Address: If the M bit is set to 1, this field contains a 6-octet + Ethernet MAC address. If the M bit is set to 0, this field MUST + be set to all zeroes on transmission and disregarded on receipt. + + Reserved: MUST be set to zero on transmission and disregarded on + receipt. + + When forming the NVGRE encapsulation header: + + * The values of the V, M, and R bits are NOT copied into the Flags + field of the NVGRE header. The Flags field of the NVGRE header is + set as per [RFC7637]. + + * If the M bit is set to 1, the MAC Address is copied into the Inner + Destination MAC Address field of the Inner Ethernet Header (see + Section 3.2 of [RFC7637]). + + If the M bit is set to 0, and the payload being sent through the + NVGRE tunnel is an Ethernet frame, the Destination MAC Address + field of the Inner Ethernet Header is just the Destination MAC + Address field of the payload's Ethernet header. + + If the M bit is set to 0, and the payload being sent through the + NVGRE tunnel is an IP or MPLS packet, the Inner Destination MAC + Address field is set to a configured value; if there is no + configured value, the NVGRE tunnel cannot be used. + + * If the V bit is set to 0, and the BGP UPDATE message has an AFI/ + SAFI other than Ethernet VPNs (EVPNs), then the NVGRE tunnel + cannot be used. + + * Section 9 describes how the VSID field of the NVGRE encapsulation + header is set. + +3.2.3. L2TPv3 (Tunnel Type 1) + + When the tunnel type of the TLV is L2TPv3 over IP [RFC3931], the + length of the sub-TLV is between 4 and 12 octets, depending on the + length of the cookie. The structure of the Value field of the + Encapsulation sub-TLV is shown in Figure 6. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Session ID (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + | Cookie (variable) | + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: L2TPv3 Encapsulation Sub-TLV Value Field + + Session ID: A non-zero 4-octet value locally assigned by the + advertising router that serves as a lookup key for the incoming + packet's context. + + Cookie: An optional, variable-length (encoded in 0 to 8 octets) + value used by L2TPv3 to check the association of a received data + message with the session identified by the Session ID. Generation + and usage of the cookie value is as specified in [RFC3931]. + + The length of the cookie is not encoded explicitly but can be + calculated as (sub-TLV length - 4). + +3.2.4. GRE (Tunnel Type 2) + + When the tunnel type of the TLV is GRE [RFC2784], the length of the + sub-TLV is 4 octets. The structure of the Value field of the + Encapsulation sub-TLV is shown in Figure 7. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | GRE Key (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 7: GRE Encapsulation Sub-TLV Value Field + + GRE Key: 4-octet field [RFC2890] that is generated by the + advertising router. Note that the key is optional. Unless a key + value is being advertised, the GRE Encapsulation sub-TLV MUST NOT + be present. + +3.2.5. MPLS-in-GRE (Tunnel Type 11) + + When the tunnel type is MPLS-in-GRE [RFC4023], the length of the sub- + TLV is 4 octets. The structure of the Value field of the + Encapsulation sub-TLV is shown in Figure 8. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | GRE Key (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 8: MPLS-in-GRE Encapsulation Sub-TLV Value Field + + GRE Key: 4-octet field [RFC2890] that is generated by the + advertising router. Note that the key is optional. Unless a key + value is being advertised, the MPLS-in-GRE Encapsulation sub-TLV + MUST NOT be present. + + Note that the GRE tunnel type defined in Section 3.2.4 can be used + instead of the MPLS-in-GRE tunnel type when it is necessary to + encapsulate MPLS in GRE. Including a TLV of the MPLS-in-GRE tunnel + type is equivalent to including a TLV of the GRE tunnel type that + also includes a Protocol Type sub-TLV (Section 3.4.1) specifying MPLS + as the protocol to be encapsulated. + + Although the MPLS-in-GRE tunnel type is just a special case of the + GRE tunnel type and thus is not strictly necessary, it is included + for reasons of backwards compatibility with, for example, + implementations of [RFC8365]. + +3.3. Outer Encapsulation Sub-TLVs + + The Encapsulation sub-TLV for a particular tunnel type allows one to + specify the values that are to be placed in certain fields of the + encapsulation header for that tunnel type. However, some tunnel + types require an outer IP encapsulation, and some also require an + outer UDP encapsulation. The Encapsulation sub-TLV for a given + tunnel type does not usually provide a way to specify values for + fields of the outer IP and/or UDP encapsulations. If it is necessary + to specify values for fields of the outer encapsulation, additional + sub-TLVs must be used. This document defines two such sub-TLVs. + + If an outer Encapsulation sub-TLV occurs in a TLV for a tunnel type + that does not use the corresponding outer encapsulation, the sub-TLV + MUST be treated as if it were an unrecognized type of sub-TLV. + +3.3.1. DS Field (Type Code 7) + + Most of the tunnel types that can be specified in the Tunnel + Encapsulation attribute require an outer IP encapsulation. The + Differentiated Services (DS) Field sub-TLV can be carried in the TLV + of any such tunnel type. It specifies the setting of the one-octet + Differentiated Services field in the outer IPv4 or IPv6 encapsulation + (see [RFC2474]). Any one-octet value can be transported; the + semantics of the DSCP (Differentiated Services Code Point) field is + beyond the scope of this document. The Value field is always a + single octet. + + 0 1 2 3 4 5 6 7 + +-+-+-+-+-+-+-+-+ + | DS value | + +-+-+-+-+-+-+-+-+ + + Figure 9: DS Field Sub-TLV Value Field + + Because the interpretation of the DSCP field at the recipient may be + different from its interpretation at the originator, an + implementation MAY provide a facility to use policy to filter or + modify the DS field. + +3.3.2. UDP Destination Port (Type Code 8) + + Some of the tunnel types that can be specified in the Tunnel + Encapsulation attribute require an outer UDP encapsulation. + Generally, there is a standard UDP destination port value for a + particular tunnel type. However, sometimes it is useful to be able + to use a nonstandard UDP destination port. If a particular tunnel + type requires an outer UDP encapsulation, and it is desired to use a + UDP destination port other than the standard one, the port to be used + can be specified by including a UDP Destination Port sub-TLV. The + Value field of this sub-TLV is always a two-octet field, containing + the port value. Any two-octet value other than zero can be + transported. If the reserved value zero is received, the sub-TLV + MUST be treated as malformed, according to the rules of Section 13. + + 0 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | UDP Port (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 10: UDP Destination Port Sub-TLV Value Field + +3.4. Sub-TLVs for Aiding Tunnel Selection + +3.4.1. Protocol Type Sub-TLV (Type Code 2) + + The Protocol Type sub-TLV MAY be included in a given TLV to indicate + the type of the payload packets that are allowed to be encapsulated + with the tunnel parameters that are being signaled in the TLV. + Packets with other payload types MUST NOT be encapsulated in the + relevant tunnel. The Value field of the sub-TLV contains a 2-octet + value from IANA's "ETHER TYPES" registry [IANA-ETHERTYPES]. If the + reserved value 0xFFFF is received, the sub-TLV MUST be treated as + malformed according to the rules of Section 13. + + 0 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Ethertype (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 11: Protocol Type Sub-TLV Value Field + + For example, if there are three L2TPv3 sessions, one carrying IPv4 + packets, one carrying IPv6 packets, and one carrying MPLS packets, + the egress router will include three TLVs of L2TPv3 encapsulation + type, each specifying a different Session ID and a different payload + type. The Protocol Type sub-TLV for these will be IPv4 (protocol + type = 0x0800), IPv6 (protocol type = 0x86dd), and MPLS (protocol + type = 0x8847), respectively. This informs the ingress routers of + the appropriate encapsulation information to use with each of the + given protocol types. Insertion of the specified Session ID at the + ingress routers allows the egress to process the incoming packets + correctly, according to their protocol type. + + Note that for tunnel types whose names are of the form "X-in-Y" (for + example, MPLS-in-GRE), only packets of the specified payload type "X" + are to be carried through the tunnel of type "Y". This is the + equivalent of specifying a tunnel type "Y" and including in its TLV a + Protocol Type sub-TLV (see Section 3.4.1) specifying protocol "X". + If the tunnel type is "X-in-Y", it is unnecessary, though harmless, + to explicitly include a Protocol Type sub-TLV specifying "X". Also, + for "X-in-Y" type tunnels, a Protocol Type sub-TLV specifying + anything other than "X" MUST be ignored; this is discussed further in + Section 13. + +3.4.2. Color Sub-TLV (Type Code 4) + + The Color sub-TLV MAY be used as a way to "color" the corresponding + Tunnel TLV. The Value field of the sub-TLV is eight octets long and + consists of a Color Extended Community, as defined in Section 4.3. + For the use of this sub-TLV and extended community, please see + Section 8. + + The format of the Value field is depicted in Figure 15. + + If the Length field of a Color sub-TLV has a value other than 8, or + the first two octets of its Value field are not 0x030b, the sub-TLV + MUST be treated as if it were an unrecognized sub-TLV (see + Section 13). + +3.5. Embedded Label Handling Sub-TLV (Type Code 9) + + Certain BGP address families (corresponding to particular AFI/SAFI + pairs, for example, 1/4, 2/4, 1/128, 2/128) have MPLS labels embedded + in their NLRIs. The term "embedded label" is used to refer to the + MPLS label that is embedded in an NLRI, and the term "labeled address + family" to refer to any AFI/SAFI that has embedded labels. + + Some of the tunnel types (for example, VXLAN and NVGRE) that can be + specified in the Tunnel Encapsulation attribute have an encapsulation + header containing a virtual network identifier of some sort. The + Encapsulation sub-TLVs for these tunnel types may optionally specify + a value for the virtual network identifier. + + Suppose a Tunnel Encapsulation attribute is attached to an UPDATE of + a labeled address family, and it is decided to use a particular + tunnel (specified in one of the attribute's TLVs) for transmitting a + packet that is being forwarded according to that UPDATE. When + forming the encapsulation header for that packet, different + deployment scenarios require different handling of the embedded label + and/or the virtual network identifier. The Embedded Label Handling + sub-TLV can be used to control the placement of the embedded label + and/or the virtual network identifier in the encapsulation. + + The Embedded Label Handling sub-TLV may be included in any TLV of the + Tunnel Encapsulation attribute. If the Tunnel Encapsulation + attribute is attached to an UPDATE of a non-labeled address family, + then the sub-TLV MUST be disregarded. If the sub-TLV is contained in + a TLV whose tunnel type does not have a virtual network identifier in + its encapsulation header, the sub-TLV MUST be disregarded. In those + cases where the sub-TLV is ignored, it MUST NOT be stripped from the + TLV before the route is propagated. + + The sub-TLV's Length field always contains the value 1, and its Value + field consists of a single octet. The following values are defined: + + 1: The payload will be an MPLS packet with the embedded label at the + top of its label stack. + + 2: The embedded label is not carried in the payload but is either + carried in the Virtual Network Identifier field of the + encapsulation header or else ignored entirely. + + If any value other than 1 or 2 is carried, the sub-TLV MUST be + considered malformed, according to the procedures of Section 13. + + Please see Section 9 for the details of how this sub-TLV is used when + it is carried by an UPDATE of a labeled address family. + + 0 1 2 3 4 5 6 7 + +-+-+-+-+-+-+-+-+ + | 1 or 2 | + +-+-+-+-+-+-+-+-+ + + Figure 12: Embedded Label Handling Sub-TLV Value Field + +3.6. MPLS Label Stack Sub-TLV (Type Code 10) + + This sub-TLV allows an MPLS label stack [RFC3032] to be associated + with a particular tunnel. + + The length of the sub-TLV is a multiple of 4 octets, and the Value + field of this sub-TLV is a sequence of MPLS label stack entries. The + first entry in the sequence is the "topmost" label, and the final + entry in the sequence is the "bottommost" label. When this label + stack is pushed onto a packet, this ordering MUST be preserved. + + Each label stack entry has the format shown in Figure 13. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Label | TC |S| TTL | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 13: MPLS Label Stack Sub-TLV Value Field + + The fields are as defined in [RFC3032] and [RFC5462]. + + If a packet is to be sent through the tunnel identified in a + particular TLV, and if that TLV contains an MPLS Label Stack sub-TLV, + then the label stack appearing in the sub-TLV MUST be pushed onto the + packet before any other labels are pushed onto the packet. (See + Section 6 for further discussion.) + + In particular, if the Tunnel Encapsulation attribute is attached to a + BGP UPDATE of a labeled address family, the contents of the MPLS + Label Stack sub-TLV MUST be pushed onto the packet before the label + embedded in the NLRI is pushed onto the packet. + + If the MPLS Label Stack sub-TLV is included in a TLV identifying a + tunnel type that uses virtual network identifiers (see Section 9), + the contents of the MPLS Label Stack sub-TLV MUST be pushed onto the + packet before the procedures of Section 9 are applied. + + The number of label stack entries in the sub-TLV MUST be determined + from the Sub-TLV Length field. Thus, it is not necessary to set the + S bit in any of the label stack entries of the sub-TLV, and the + setting of the S bit is ignored when parsing the sub-TLV. When the + label stack entries are pushed onto a packet that already has a label + stack, the S bits of all the entries being pushed MUST be cleared. + When the label stack entries are pushed onto a packet that does not + already have a label stack, the S bit of the bottommost label stack + entry MUST be set, and the S bit of all the other label stack entries + MUST be cleared. + + The Traffic Class (TC) field [RFC3270][RFC5129] of each label stack + entry SHOULD be set to 0, unless changed by policy at the originator + of the sub-TLV. When pushing the label stack onto a packet, the TC + of each label stack SHOULD be preserved, unless local policy results + in a modification. + + The TTL (Time to Live) field of each label stack entry SHOULD be set + to 255, unless changed to some other non-zero value by policy at the + originator of the sub-TLV. When pushing the label stack onto a + packet, the TTL of each label stack entry SHOULD be preserved, unless + local policy results in a modification to some other non-zero value. + If any label stack entry in the sub-TLV has a TTL value of zero, the + router that is pushing the stack onto a packet MUST change the value + to a non-zero value, either 255 or some other value as determined by + policy as discussed above. + + Note that this sub-TLV can appear within a TLV identifying any type + of tunnel, not just within a TLV identifying an MPLS tunnel. + However, if this sub-TLV appears within a TLV identifying an MPLS + tunnel (or an MPLS-in-X tunnel), this sub-TLV plays the same role + that would be played by an MPLS Encapsulation sub-TLV. Therefore, an + MPLS Encapsulation sub-TLV is not defined. + + Although this specification does not supply detailed instructions for + validating the received label stack, implementations might impose + restrictions on the label stack they can support. If an invalid or + unsupported label stack is received, the tunnel MAY be treated as not + feasible, according to the procedures of Section 6. + +3.7. Prefix-SID Sub-TLV (Type Code 11) + + [RFC8669] defines a BGP path attribute known as the "BGP Prefix-SID + attribute". This attribute is defined to contain a sequence of one + or more TLVs, where each TLV is either a Label-Index TLV or an + Originator SRGB (Source Routing Global Block) TLV. + + This document defines a Prefix-SID (Prefix Segment Identifier) sub- + TLV. The Value field of the Prefix-SID sub-TLV can be set to any + permitted value of the Value field of a BGP Prefix-SID attribute + [RFC8669]. + + [RFC8669] only defines behavior when the BGP Prefix-SID attribute is + attached to routes of type IPv4/IPv6 Labeled Unicast + [RFC4760][RFC8277], and it only defines values of the BGP Prefix-SID + attribute for those cases. Therefore, similar limitations exist for + the Prefix-SID sub-TLV: it SHOULD only be included in a BGP UPDATE + message for one of the address families for which [RFC8669] has a + defined behavior, namely BGP IPv4/IPv6 Labeled Unicast [RFC4760] + [RFC8277]. If included in a BGP UPDATE for any other address family, + it MUST be ignored. + + The Prefix-SID sub-TLV can occur in a TLV identifying any type of + tunnel. If an Originator SRGB is specified in the sub-TLV, that SRGB + MUST be interpreted to be the SRGB used by the tunnel's egress + endpoint. The Label-Index, if present, is the Segment Routing SID + that the tunnel's egress endpoint uses to represent the prefix + appearing in the NLRI field of the BGP UPDATE to which the Tunnel + Encapsulation attribute is attached. + + If a Label-Index is present in the Prefix-SID sub-TLV, then when a + packet is sent through the tunnel identified by the TLV, if that + tunnel is from a labeled address family, the corresponding MPLS label + MUST be pushed on the packet's label stack. The corresponding MPLS + label is computed from the Label-Index value and the SRGB of the + route's originator, as specified in Section 4.1 of [RFC8669]. + + The corresponding MPLS label is pushed on after the processing of the + MPLS Label Stack sub-TLV, if present, as specified in Section 3.6. + It is pushed on before any other labels (for example, a label + embedded in an UPDATE's NLRI or a label determined by the procedures + of Section 9) are pushed on the stack. + + The Prefix-SID sub-TLV has slightly different semantics than the BGP + Prefix-SID attribute. When the BGP Prefix-SID attribute is attached + to a given route, the BGP speaker that originally attached the + attribute is expected to be in the same Segment Routing domain as the + BGP speakers who receive the route with the attached attribute. The + Label-Index tells the receiving BGP speakers what the Prefix-SID is + for the advertised prefix in that Segment Routing domain. When the + Prefix-SID sub-TLV is used, there is no implication that the Prefix- + SID for the advertised prefix is the same in the Segment Routing + domains of the BGP speaker that originated the sub-TLV and the BGP + speaker that received it. + +4. Extended Communities Related to the Tunnel Encapsulation Attribute + +4.1. Encapsulation Extended Community + + The Encapsulation Extended Community is a Transitive Opaque Extended + Community. + + The Encapsulation Extended Community encoding is as shown in + Figure 14. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 0x03 (1 octet)| 0x0c (1 octet)| Reserved (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Reserved (2 octets) | Tunnel Type (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 14: Encapsulation Extended Community + + The value of the high-order octet of the extended Type field is 0x03, + which indicates it's transitive. The value of the low-order octet of + the extended Type field is 0x0c. + + The last two octets of the Value field encode a tunnel type. + + This extended community may be attached to a route of any AFI/SAFI to + which the Tunnel Encapsulation attribute may be attached. Each such + extended community identifies a particular tunnel type; its semantics + are the same as semantics of a Tunnel TLV in a Tunnel Encapsulation + attribute, for which the following three conditions all hold: + + 1. It identifies the same tunnel type. + + 2. It has a Tunnel Egress Endpoint sub-TLV for which one of the + following two conditions holds: + + a. Its Address Family subfield contains zero, or + + b. Its Address subfield contains the address of the Next Hop + field of the route to which the Tunnel Encapsulation + attribute is attached. + + 3. It has no other sub-TLVs. + + Such a Tunnel TLV is called a "barebones" Tunnel TLV. + + The Encapsulation Extended Community was first defined in [RFC5512]. + While it provides only a small subset of the functionality of the + Tunnel Encapsulation attribute, it is used in a number of deployed + applications and is still needed for backwards compatibility. In + situations where a tunnel could be encoded using a barebones TLV, it + MUST be encoded using the corresponding Encapsulation Extended + Community. Notwithstanding, an implementation MUST be prepared to + process a tunnel received encoded as a barebones TLV. + + Note that for tunnel types of the form "X-in-Y" (for example, MPLS- + in-GRE), the Encapsulation Extended Community implies that only + packets of the specified payload type "X" are to be carried through + the tunnel of type "Y". Packets with other payload types MUST NOT be + carried through such tunnels. See also Section 2. + + In the remainder of this specification, when a route is referred to + as containing a Tunnel Encapsulation attribute with a TLV identifying + a particular tunnel type, it implicitly includes the case where the + route contains an Encapsulation Extended Community identifying that + tunnel type. + +4.2. Router's MAC Extended Community + + [EVPN-INTER-SUBNET] defines a router's MAC Extended Community. This + extended community, as its name implies, carries the MAC address of + the advertising router. Since the VXLAN and NVGRE Encapsulation sub- + TLVs can also optionally carry a router's MAC, a conflict can arise + if both the Router's MAC Extended Community and such an Encapsulation + sub-TLV are present at the same time but have different values. In + case of such a conflict, the information in the Router's MAC Extended + Community MUST be used. + +4.3. Color Extended Community + + The Color Extended Community is a Transitive Opaque Extended + Community with the encoding shown in Figure 15. + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 0x03 (1 octet)| 0x0b (1 octet)| Flags (2 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Color Value (4 octets) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 15: Color Extended Community + + The value of the high-order octet of the extended Type field is 0x03, + which indicates it is transitive. The value of the low-order octet + of the extended Type field for this community is 0x0b. The color + value is user defined and configured locally. No flags are defined + in this document; this field MUST be set to zero by the originator + and ignored by the receiver; the value MUST NOT be changed when + propagating this extended community. The Color Value field is + encoded as a 4-octet value by the administrator and is outside the + scope of this document. For the use of this extended community, + please see Section 8. + +5. Special Considerations for IP-in-IP Tunnels + + In certain situations with an IP fabric underlay, one could have a + tunnel overlay with the tunnel type IP-in-IP. The egress BGP speaker + can advertise the IP-in-IP tunnel endpoint address in the Tunnel + Egress Endpoint sub-TLV. When the tunnel type of the TLV is IP-in- + IP, it will not have a virtual network identifier. However, the + tunnel egress endpoint address can be used in identifying the + forwarding table to use for making the forwarding decisions to + forward the payload. + +6. Semantics and Usage of the Tunnel Encapsulation Attribute + + The BGP Tunnel Encapsulation attribute MAY be carried in any BGP + UPDATE message whose AFI/SAFI is 1/1 (IPv4 Unicast), 2/1 (IPv6 + Unicast), 1/4 (IPv4 Labeled Unicast), 2/4 (IPv6 Labeled Unicast), + 1/128 (VPN-IPv4 Labeled Unicast), 2/128 (VPN-IPv6 Labeled Unicast), + or 25/70 (Ethernet VPN, usually known as EVPN). Use of the Tunnel + Encapsulation attribute in BGP UPDATE messages of other AFI/SAFIs is + outside the scope of this document. + + There is no significance to the order in which the TLVs occur within + the Tunnel Encapsulation attribute. Multiple TLVs may occur for a + given tunnel type; each such TLV is regarded as describing a + different tunnel. (This also applies if the Encapsulation Extended + Community encoding is used.) + + The decision to attach a Tunnel Encapsulation attribute to a given + BGP UPDATE is determined by policy. The set of TLVs and sub-TLVs + contained in the attribute is also determined by policy. + + Suppose that: + + * a given packet P must be forwarded by router R; + + * the path along which P is to be forwarded is determined by BGP + UPDATE U; + + * UPDATE U has a Tunnel Encapsulation attribute, containing at least + one TLV that identifies a "feasible tunnel" for packet P. A + tunnel is considered feasible if it has the following four + properties: + + 1. The tunnel type is supported (that is, router R knows how to + set up tunnels of that type, how to create the encapsulation + header for tunnels of that type, etc.). + + 2. The tunnel is of a type that can be used to carry packet P + (for example, an MPLS-in-UDP tunnel would not be a feasible + tunnel for carrying an IP packet, unless the IP packet can + first be encapsulated in a MPLS packet). + + 3. The tunnel is specified in a TLV whose Tunnel Egress Endpoint + sub-TLV identifies an IP address that is reachable. The + reachability condition is evaluated as per [RFC4271]. If the + IP address is reachable via more than one forwarding table, + local policy is used to determine which table to use. + + 4. There is no local policy that prevents the use of the tunnel. + + Then router R MUST send packet P through one of the feasible tunnels + identified in the Tunnel Encapsulation attribute of UPDATE U. + + If the Tunnel Encapsulation attribute contains several TLVs (that is, + if it specifies several feasible tunnels), router R may choose any + one of those tunnels, based upon local policy. If any Tunnel TLV + contains one or more Color sub-TLVs (Section 3.4.2) and/or the + Protocol Type sub-TLV (Section 3.4.1), the choice of tunnel may be + influenced by these sub-TLVs. Many other factors, for example, + minimization of encapsulation-header overhead, could also be used to + influence selection. + + The reachability to the address of the egress endpoint of the tunnel + may change over time, directly impacting the feasibility of the + tunnel. A tunnel that is not feasible at some moment may become + feasible at a later time when its egress endpoint address is + reachable. The router may start using the newly feasible tunnel + instead of an existing one. How this decision is made is outside the + scope of this document. + + Once it is determined to send a packet through the tunnel specified + in a particular Tunnel TLV of a particular Tunnel Encapsulation + attribute, then the tunnel's egress endpoint address is the IP + address contained in the Tunnel Egress Endpoint sub-TLV. If the + Tunnel TLV contains a Tunnel Egress Endpoint sub-TLV whose Value + field is all zeroes, then the tunnel's egress endpoint is the address + of the next hop of the BGP UPDATE containing the Tunnel Encapsulation + attribute (that is, the Network Address of Next Hop field of the + MP_REACH_NLRI attribute if the encoding of [RFC4760] is in use or the + NEXT_HOP attribute otherwise). The address of the tunnel egress + endpoint generally appears in a Destination Address field of the + encapsulation. + + The full set of procedures for sending a packet through a particular + tunnel type to a particular tunnel egress endpoint depends upon the + tunnel type and is outside the scope of this document. Note that + some tunnel types may require the execution of an explicit tunnel + setup protocol before they can be used for carrying data. Other + tunnel types may not require any tunnel setup protocol. + + Sending a packet through a tunnel always requires that the packet be + encapsulated, with an encapsulation header that is appropriate for + the tunnel type. The contents of the tunnel encapsulation header may + be influenced by the Encapsulation sub-TLV. If there is no + Encapsulation sub-TLV present, the router transmitting the packet + through the tunnel must have a priori knowledge (for example, by + provisioning) of how to fill in the various fields in the + encapsulation header. + + A Tunnel Encapsulation attribute may contain several TLVs that all + specify the same tunnel type. Each TLV should be considered as + specifying a different tunnel. Two tunnels of the same type may have + different Tunnel Egress Endpoint sub-TLVs, different Encapsulation + sub-TLVs, etc. Choosing between two such tunnels is a matter of + local policy. + + Once router R has decided to send packet P through a particular + tunnel, it encapsulates packet P appropriately and then forwards it + according to the route that leads to the tunnel's egress endpoint. + This route may itself be a BGP route with a Tunnel Encapsulation + attribute. If so, the encapsulated packet is treated as the payload + and encapsulated according to the Tunnel Encapsulation attribute of + that route. That is, tunnels may be "stacked". + + Notwithstanding anything said in this document, a BGP speaker MAY + have local policy that influences the choice of tunnel and the way + the encapsulation is formed. A BGP speaker MAY also have a local + policy that tells it to ignore the Tunnel Encapsulation attribute + entirely or in part. Of course, interoperability issues must be + considered when such policies are put into place. + + See also Section 13, which provides further specification regarding + validation and exception cases. + +7. Routing Considerations + +7.1. Impact on the BGP Decision Process + + The presence of the Tunnel Encapsulation attribute affects the BGP + best route-selection algorithm. If a route includes the Tunnel + Encapsulation attribute, and if that attribute includes no tunnel + that is feasible, then that route MUST NOT be considered resolvable + for the purposes of the route resolvability condition ([RFC4271], + Section 9.1.2.1). + +7.2. Looping, Mutual Recursion, Etc. + + Consider a packet destined for address X. Suppose a BGP UPDATE for + address prefix X carries a Tunnel Encapsulation attribute that + specifies a tunnel egress endpoint of Y, and suppose that a BGP + UPDATE for address prefix Y carries a Tunnel Encapsulation attribute + that specifies a tunnel egress endpoint of X. It is easy to see that + this can have no good outcome. [RFC4271] describes an analogous case + as mutually recursive routes. + + This could happen as a result of misconfiguration, either accidental + or intentional. It could also happen if the Tunnel Encapsulation + attribute were altered by a malicious agent. Implementations should + be aware that such an attack will result in unresolvable BGP routes + due to the mutually recursive relationship. This document does not + specify a maximum number of recursions; that is an implementation- + specific matter. + + Improper setting (or malicious altering) of the Tunnel Encapsulation + attribute could also cause data packets to loop. Suppose a BGP + UPDATE for address prefix X carries a Tunnel Encapsulation attribute + that specifies a tunnel egress endpoint of Y. Suppose router R + receives and processes the advertisement. When router R receives a + packet destined for X, it will apply the encapsulation and send the + encapsulated packet to Y. Y will decapsulate the packet and forward + it further. If Y is further away from X than is router R, it is + possible that the path from Y to X will traverse R. This would cause + a long-lasting routing loop. The control plane itself cannot detect + this situation, though a TTL field in the payload packets would + prevent any given packet from looping infinitely. + + During the deployment of techniques described in this document, + operators are encouraged to avoid mutually recursive route and/or + tunnel dependencies. There is greater potential for such scenarios + to arise when the tunnel egress endpoint for a given prefix differs + from the address of the next hop for that prefix. + +8. Recursive Next-Hop Resolution + + Suppose that: + + * a given packet P must be forwarded by router R1; + + * the path along which P is to be forwarded is determined by BGP + UPDATE U1; + + * UPDATE U1 does not have a Tunnel Encapsulation attribute; + + * the address of the next hop of UPDATE U1 is router R2; + + * the best route to router R2 is a BGP route that was advertised in + UPDATE U2; and + + * UPDATE U2 has a Tunnel Encapsulation attribute. + + Then packet P MUST be sent through one of the tunnels identified in + the Tunnel Encapsulation attribute of UPDATE U2. See Section 6 for + further details. + + However, suppose that one of the TLVs in U2's Tunnel Encapsulation + attribute contains one or more Color sub-TLVs. In that case, packet + P MUST NOT be sent through the tunnel contained in that TLV, unless + U1 is carrying a Color Extended Community that is identified in one + of U2's Color sub-TLVs. + + The procedures in this section presuppose that U1's address of the + next hop resolves to a BGP route, and that U2's next hop resolves + (perhaps after further recursion) to a non-BGP route. + +9. Use of Virtual Network Identifiers and Embedded Labels When Imposing + a Tunnel Encapsulation + + If the TLV specifying a tunnel contains an MPLS Label Stack sub-TLV, + then when sending a packet through that tunnel, the procedures of + Section 3.6 are applied before the procedures of this section. + + If the TLV specifying a tunnel contains a Prefix-SID sub-TLV, the + procedures of Section 3.7 are applied before the procedures of this + section. If the TLV also contains an MPLS Label Stack sub-TLV, the + procedures of Section 3.6 are applied before the procedures of + Section 3.7. + +9.1. Tunnel Types without a Virtual Network Identifier Field + + If a Tunnel Encapsulation attribute is attached to an UPDATE of a + labeled address family, there will be one or more labels specified in + the UPDATE's NLRI. When a packet is sent through a tunnel specified + in one of the attribute's TLVs, and that tunnel type does not contain + a Virtual Network Identifier field, the label or labels from the NLRI + are pushed on the packet's label stack. The resulting MPLS packet is + then further encapsulated, as specified by the TLV. + +9.2. Tunnel Types with a Virtual Network Identifier Field + + Two of the tunnel types that can be specified in a Tunnel + Encapsulation TLV have Virtual Network Identifier fields in their + encapsulation headers. In the VXLAN encapsulation, this field is + called the VNI (VXLAN Network Identifier) field; in the NVGRE + encapsulation, this field is called the VSID (Virtual Subnet + Identifier) field. + + When one of these tunnel encapsulations is imposed on a packet, the + setting of the Virtual Network Identifier field in the encapsulation + header depends upon the contents of the Encapsulation sub-TLV (if one + is present). When the Tunnel Encapsulation attribute is being + carried in a BGP UPDATE of a labeled address family, the setting of + the Virtual Network Identifier field also depends upon the contents + of the Embedded Label Handling sub-TLV (if present). + + This section specifies the procedures for choosing the value to set + in the Virtual Network Identifier field of the encapsulation header. + These procedures apply only when the tunnel type is VXLAN or NVGRE. + +9.2.1. Unlabeled Address Families + + This subsection applies when: + + * the Tunnel Encapsulation attribute is carried in a BGP UPDATE of + an unlabeled address family, + + * at least one of the attribute's TLVs identifies a tunnel type that + uses a virtual network identifier, and + + * it has been determined to send a packet through one of those + tunnels. + + If the TLV identifying the tunnel contains an Encapsulation sub-TLV + whose V bit is set to 1, the Virtual Network Identifier field of the + encapsulation header is set to the value of the Virtual Network + Identifier field of the Encapsulation sub-TLV. + + Otherwise, the Virtual Network Identifier field of the encapsulation + header is set to a configured value; if there is no configured value, + the tunnel cannot be used. + +9.2.2. Labeled Address Families + + This subsection applies when: + + * the Tunnel Encapsulation attribute is carried in a BGP UPDATE of a + labeled address family, + + * at least one of the attribute's TLVs identifies a tunnel type that + uses a virtual network identifier, and + + * it has been determined to send a packet through one of those + tunnels. + +9.2.2.1. When a Valid VNI Has Been Signaled + + If the TLV identifying the tunnel contains an Encapsulation sub-TLV + whose V bit is set to 1, the Virtual Network Identifier field of the + encapsulation header is set to the value of the Virtual Network + Identifier field of the Encapsulation sub-TLV. However, the Embedded + Label Handling sub-TLV will determine label processing as described + below. + + * If the TLV contains an Embedded Label Handling sub-TLV whose value + is 1, the embedded label (from the NLRI of the route that is + carrying the Tunnel Encapsulation attribute) appears at the top of + the MPLS label stack in the encapsulation payload. + + * If the TLV does not contain an Embedded Label Handling sub-TLV, or + it contains an Embedded Label Handling sub-TLV whose value is 2, + the embedded label is ignored entirely. + +9.2.2.2. When a Valid VNI Has Not Been Signaled + + If the TLV identifying the tunnel does not contain an Encapsulation + sub-TLV whose V bit is set to 1, the Virtual Network Identifier field + of the encapsulation header is set as follows: + + * If the TLV contains an Embedded Label Handling sub-TLV whose value + is 1, then the Virtual Network Identifier field of the + encapsulation header is set to a configured value. + + If there is no configured value, the tunnel cannot be used. + + The embedded label (from the NLRI of the route that is carrying + the Tunnel Encapsulation attribute) appears at the top of the MPLS + label stack in the encapsulation payload. + + * If the TLV does not contain an Embedded Label Handling sub-TLV, or + if it contains an Embedded Label Handling sub-TLV whose value is + 2, the embedded label is copied into the lower 3 octets of the + Virtual Network Identifier field of the encapsulation header. + + In this case, the payload may or may not contain an MPLS label + stack, depending upon other factors. If the payload does contain + an MPLS label stack, the embedded label does not appear in that + stack. + +10. Applicability Restrictions + + In a given UPDATE of a labeled address family, the label embedded in + the NLRI is generally a label that is meaningful only to the router + represented by the address of the next hop. Certain of the + procedures of Sections 9.2.2.1 or 9.2.2.2 cause the embedded label to + be carried by a data packet to the router whose address appears in + the Tunnel Egress Endpoint sub-TLV. If the Tunnel Egress Endpoint + sub-TLV does not identify the same router represented by the address + of the next hop, sending the packet through the tunnel may cause the + label to be misinterpreted at the tunnel's egress endpoint. This may + cause misdelivery of the packet. Avoidance of this unfortunate + outcome is a matter of network planning and design and is outside the + scope of this document. + + Note that if the Tunnel Encapsulation attribute is attached to a VPN- + IP route [RFC4364], if Inter-AS "option b" (see Section 10 of + [RFC4364]) is being used, and if the Tunnel Egress Endpoint sub-TLV + contains an IP address that is not in the same AS as the router + receiving the route, it is very likely that the embedded label has + been changed. Therefore, use of the Tunnel Encapsulation attribute + in an "Inter-AS option b" scenario is not recommended. + + Other documents may define other ways to signal tunnel information in + BGP. For example, [RFC6514] defines the "P-Multicast Service + Interface Tunnel" (PMSI Tunnel) attribute. In this specification, we + do not consider the effects of advertising the Tunnel Encapsulation + attribute in conjunction with other forms of signaling tunnels. Any + document specifying such joint use MUST provide details as to how + interactions should be handled. + +11. Scoping + + The Tunnel Encapsulation attribute is defined as a transitive + attribute, so that it may be passed along by BGP speakers that do not + recognize it. However, the Tunnel Encapsulation attribute MUST be + used only within a well-defined scope, for example, within a set of + ASes that belong to a single administrative entity. If the attribute + is distributed beyond its intended scope, packets may be sent through + tunnels in a manner that is not intended. + + To prevent the Tunnel Encapsulation attribute from being distributed + beyond its intended scope, any BGP speaker that understands the + attribute MUST be able to filter the attribute from incoming BGP + UPDATE messages. When the attribute is filtered from an incoming + UPDATE, the attribute is neither processed nor distributed. This + filtering SHOULD be possible on a per-BGP-session basis; finer + granularities (for example, per route and/or per attribute TLV) MAY + be supported. For each external BGP (EBGP) session, filtering of the + attribute on incoming UPDATEs MUST be enabled by default. + + In addition, any BGP speaker that understands the attribute MUST be + able to filter the attribute from outgoing BGP UPDATE messages. This + filtering SHOULD be possible on a per-BGP-session basis. For each + EBGP session, filtering of the attribute on outgoing UPDATEs MUST be + enabled by default. + + Since the Encapsulation Extended Community provides a subset of the + functionality of the Tunnel Encapsulation attribute, these + considerations apply equally in its case: + + * Any BGP speaker that understands it MUST be able to filter it from + incoming BGP UPDATE messages. + + * It MUST be possible to filter the Encapsulation Extended Community + from outgoing messages. + + * In both cases, this filtering MUST be enabled by default for EBGP + sessions. + +12. Operational Considerations + + A potential operational difficulty arises when tunnels are used, if + the size of packets entering the tunnel exceeds the maximum + transmission unit (MTU) the tunnel is capable of supporting. This + difficulty can be exacerbated by stacking multiple tunnels, since + each stacked tunnel header further reduces the supportable MTU. This + issue is long-standing and well-known. The tunnel signaling provided + in this specification does nothing to address this issue, nor to + aggravate it (except insofar as it may further increase the + popularity of tunneling). + +13. Validation and Error Handling + + The Tunnel Encapsulation attribute is a sequence of TLVs, each of + which is a sequence of sub-TLVs. The final octet of a TLV is + determined by its Length field. Similarly, the final octet of a sub- + TLV is determined by its Length field. The final octet of a TLV MUST + also be the final octet of its final sub-TLV. If this is not the + case, the TLV MUST be considered to be malformed, and the "Treat-as- + withdraw" procedure of [RFC7606] is applied. + + If a Tunnel Encapsulation attribute does not have any valid TLVs, or + it does not have the transitive bit set, the "Treat-as-withdraw" + procedure of [RFC7606] is applied. + + If a Tunnel Encapsulation attribute can be parsed correctly but + contains a TLV whose tunnel type is not recognized by a particular + BGP speaker, that BGP speaker MUST NOT consider the attribute to be + malformed. Rather, it MUST interpret the attribute as if that TLV + had not been present. If the route carrying the Tunnel Encapsulation + attribute is propagated with the attribute, the unrecognized TLV MUST + remain in the attribute. + + The following sub-TLVs defined in this document MUST NOT occur more + than once in a given Tunnel TLV: Tunnel Egress Endpoint (discussed + below), Encapsulation, DS, UDP Destination Port, Embedded Label + Handling, MPLS Label Stack, and Prefix-SID. If a Tunnel TLV has more + than one of any of these sub-TLVs, all but the first occurrence of + each such sub-TLV type MUST be disregarded. However, the Tunnel TLV + containing them MUST NOT be considered to be malformed, and all the + sub-TLVs MUST be propagated if the route carrying the Tunnel + Encapsulation attribute is propagated. + + The following sub-TLVs defined in this document may appear zero or + more times in a given Tunnel TLV: Protocol Type and Color. Each + occurrence of such sub-TLVs is meaningful. For example, the Color + sub-TLV may appear multiple times to assign multiple colors to a + tunnel. + + If a TLV of a Tunnel Encapsulation attribute contains a sub-TLV that + is not recognized by a particular BGP speaker, the BGP speaker MUST + process that TLV as if the unrecognized sub-TLV had not been present. + If the route carrying the Tunnel Encapsulation attribute is + propagated with the attribute, the unrecognized sub-TLV MUST remain + in the attribute. + + In general, if a TLV contains a sub-TLV that is malformed, the sub- + TLV MUST be treated as if it were an unrecognized sub-TLV. There is + one exception to this rule: if a TLV contains a malformed Tunnel + Egress Endpoint sub-TLV (as defined in Section 3.1), the entire TLV + MUST be ignored and MUST be removed from the Tunnel Encapsulation + attribute before the route carrying that attribute is distributed. + + Within a Tunnel Encapsulation attribute that is carried by a BGP + UPDATE whose AFI/SAFI is one of those explicitly listed in the first + paragraph of Section 6, a TLV that does not contain exactly one + Tunnel Egress Endpoint sub-TLV MUST be treated as if it contained a + malformed Tunnel Egress Endpoint sub-TLV. + + A TLV identifying a particular tunnel type may contain a sub-TLV that + is meaningless for that tunnel type. For example, perhaps the TLV + contains a UDP Destination Port sub-TLV, but the identified tunnel + type does not use UDP encapsulation at all, or a tunnel of the form + "X-in-Y" contains a Protocol Type sub-TLV that specifies something + other than "X". Sub-TLVs of this sort MUST be disregarded. That is, + they MUST NOT affect the creation of the encapsulation header. + However, the sub-TLV MUST NOT be considered to be malformed and + MUST NOT be removed from the TLV before the route carrying the Tunnel + Encapsulation attribute is distributed. An implementation MAY log a + message when it encounters such a sub-TLV. + +14. IANA Considerations + + IANA has made the updates described in the following subsections. + All registration procedures listed are per their definitions in + [RFC8126]. + +14.1. Obsoleting RFC 5512 + + Because this document obsoletes RFC 5512, IANA has updated references + to RFC 5512 to point to this document in the following registries: + + * "Border Gateway Protocol (BGP) Extended Communities" registry + [IANA-BGP-EXT-COMM] + + * "Border Gateway Protocol (BGP) Parameters" registry + [IANA-BGP-PARAMS] + + * "Border Gateway Protocol (BGP) Tunnel Encapsulation" registry + [IANA-BGP-TUNNEL-ENCAP] + + * "Subsequent Address Family Identifiers (SAFI) Parameters" registry + [IANA-SAFI] + +14.2. Obsoleting Code Points Assigned by RFC 5566 + + Since this document obsoletes RFC 5566, the code points assigned by + that RFC are similarly obsoleted. Specifically, the following code + points have been marked as deprecated. + + In the "BGP Tunnel Encapsulation Attribute Tunnel Types" registry + [IANA-BGP-TUNNEL-ENCAP]: + + +=======+==========================================================+ + | Value | Name | + +=======+==========================================================+ + | 3 | Transmit tunnel endpoint (DEPRECATED) | + +-------+----------------------------------------------------------+ + | 4 | IPsec in Tunnel-mode (DEPRECATED) | + +-------+----------------------------------------------------------+ + | 5 | IP in IP tunnel with IPsec Transport Mode (DEPRECATED) | + +-------+----------------------------------------------------------+ + | 6 | MPLS-in-IP tunnel with IPsec Transport Mode (DEPRECATED) | + +-------+----------------------------------------------------------+ + + Table 1 + + And in the "BGP Tunnel Encapsulation Attribute Sub-TLVs" registry + [IANA-BGP-TUNNEL-ENCAP]: + + +=======+=========================================+ + | Value | Name | + +=======+=========================================+ + | 3 | IPsec Tunnel Authenticator (DEPRECATED) | + +-------+-----------------------------------------+ + + Table 2 + +14.3. Border Gateway Protocol (BGP) Tunnel Encapsulation Grouping + + IANA has created a new registry grouping named "Border Gateway + Protocol (BGP) Tunnel Encapsulation" [IANA-BGP-TUNNEL-ENCAP]. + +14.4. BGP Tunnel Encapsulation Attribute Tunnel Types + + IANA has relocated the "BGP Tunnel Encapsulation Attribute Tunnel + Types" registry to be under the "Border Gateway Protocol (BGP) Tunnel + Encapsulation" grouping [IANA-BGP-TUNNEL-ENCAP]. + +14.5. Subsequent Address Family Identifiers + + IANA has modified the "SAFI Values" registry [IANA-SAFI] to indicate + that the Encapsulation SAFI (value 7) has been obsoleted. This + document is listed as the reference for this change. + +14.6. BGP Tunnel Encapsulation Attribute Sub-TLVs + + IANA has relocated the "BGP Tunnel Encapsulation Attribute Sub-TLVs" + registry to be under the "Border Gateway Protocol (BGP) Tunnel + Encapsulation" grouping [IANA-BGP-TUNNEL-ENCAP]. + + IANA has included the following note to the registry: + + | If the Sub-TLV Type is in the range from 0 to 127 (inclusive), the + | Sub-TLV Length field contains one octet. If the Sub-TLV Type is + | in the range from 128 to 255 (inclusive), the Sub-TLV Length field + | contains two octets. + + IANA has updated the registration procedures of the registry to the + following: + + +=========+=========================+ + | Range | Registration Procedures | + +=========+=========================+ + | 1-63 | Standards Action | + +---------+-------------------------+ + | 64-125 | First Come First Served | + +---------+-------------------------+ + | 126-127 | Experimental Use | + +---------+-------------------------+ + | 128-191 | Standards Action | + +---------+-------------------------+ + | 192-252 | First Come First Served | + +---------+-------------------------+ + | 253-254 | Experimental Use | + +---------+-------------------------+ + + Table 3 + + IANA has added the following entries to this registry: + + +=======+=========================+===========+ + | Value | Description | Reference | + +=======+=========================+===========+ + | 0 | Reserved | RFC 9012 | + +-------+-------------------------+-----------+ + | 6 | Tunnel Egress Endpoint | RFC 9012 | + +-------+-------------------------+-----------+ + | 7 | DS Field | RFC 9012 | + +-------+-------------------------+-----------+ + | 8 | UDP Destination Port | RFC 9012 | + +-------+-------------------------+-----------+ + | 9 | Embedded Label Handling | RFC 9012 | + +-------+-------------------------+-----------+ + | 10 | MPLS Label Stack | RFC 9012 | + +-------+-------------------------+-----------+ + | 11 | Prefix-SID | RFC 9012 | + +-------+-------------------------+-----------+ + | 255 | Reserved | RFC 9012 | + +-------+-------------------------+-----------+ + + Table 4 + +14.7. Flags Field of VXLAN Encapsulation Sub-TLV + + IANA has created a registry named "Flags Field of VXLAN Encapsulation + Sub-TLVs" under the "Border Gateway Protocol (BGP) Tunnel + Encapsulation" grouping [IANA-BGP-TUNNEL-ENCAP]. The registration + policy for this registry is "Standards Action". The minimum possible + value is 0, and the maximum is 7. + + The initial values for this new registry are indicated in Table 5. + + +==============+=================+===========+ + | Bit Position | Description | Reference | + +==============+=================+===========+ + | 0 | V (VN-ID) | RFC 9012 | + +--------------+-----------------+-----------+ + | 1 | M (MAC Address) | RFC 9012 | + +--------------+-----------------+-----------+ + + Table 5 + +14.8. Flags Field of NVGRE Encapsulation Sub-TLV + + IANA has created a registry named "Flags Field of NVGRE Encapsulation + Sub-TLVs" under the "Border Gateway Protocol (BGP) Tunnel + Encapsulation" grouping [IANA-BGP-TUNNEL-ENCAP]. The registration + policy for this registry is "Standards Action". The minimum possible + value is 0, and the maximum is 7. + + The initial values for this new registry are indicated in Table 6. + + +==============+=================+===========+ + | Bit Position | Description | Reference | + +==============+=================+===========+ + | 0 | V (VN-ID) | RFC 9012 | + +--------------+-----------------+-----------+ + | 1 | M (MAC Address) | RFC 9012 | + +--------------+-----------------+-----------+ + + Table 6 + +14.9. Embedded Label Handling Sub-TLV + + IANA has created a registry named "Embedded Label Handling Sub-TLVs" + under the "Border Gateway Protocol (BGP) Tunnel Encapsulation" + grouping [IANA-BGP-TUNNEL-ENCAP]. The registration policy for this + registry is "Standards Action". The minimum possible value is 0, and + the maximum is 255. + + The initial values for this new registry are indicated in Table 7. + + +=======+=====================================+===========+ + | Value | Description | Reference | + +=======+=====================================+===========+ + | 0 | Reserved | RFC 9012 | + +-------+-------------------------------------+-----------+ + | 1 | Payload of MPLS with embedded label | RFC 9012 | + +-------+-------------------------------------+-----------+ + | 2 | No embedded label in payload | RFC 9012 | + +-------+-------------------------------------+-----------+ + + Table 7 + +14.10. Color Extended Community Flags + + IANA has created a registry named "Color Extended Community Flags" + under the "Border Gateway Protocol (BGP) Tunnel Encapsulation" + grouping [IANA-BGP-TUNNEL-ENCAP]. The registration policy for this + registry is "Standards Action". The minimum possible value is 0, and + the maximum is 15. + + This new registry contains columns for "Bit Position", "Description", + and "Reference". No values have currently been registered. + +15. Security Considerations + + As Section 11 discusses, it is intended that the Tunnel Encapsulation + attribute be used only within a well-defined scope, for example, + within a set of ASes that belong to a single administrative entity. + As long as the filtering mechanisms discussed in that section are + applied diligently, an attacker outside the scope would not be able + to use the Tunnel Encapsulation attribute in an attack. This leaves + open the questions of attackers within the scope (for example, a + compromised router) and failures in filtering that allow an external + attack to succeed. + + As [RFC4272] discusses, BGP is vulnerable to traffic-diversion + attacks. The Tunnel Encapsulation attribute adds a new means by + which an attacker could cause traffic to be diverted from its normal + path, especially when the Tunnel Egress Endpoint sub-TLV is used. + Such an attack would differ from pre-existing vulnerabilities in that + traffic could be tunneled to a distant target across intervening + network infrastructure, allowing an attack to potentially succeed + more easily, since less infrastructure would have to be subverted. + Potential consequences include "hijacking" of traffic (insertion of + an undesired node in the path, which allows for inspection or + modification of traffic, or avoidance of security controls) or denial + of service (directing traffic to a node that doesn't desire to + receive it). + + In order to further mitigate the risk of diversion of traffic from + its intended destination, Section 3.1.1 provides an optional + procedure to check that the destination given in a Tunnel Egress + Endpoint sub-TLV is within the AS that was the source of the route. + One then has some level of assurance that the tunneled traffic is + going to the same destination AS that it would have gone to had the + Tunnel Encapsulation attribute not been present. As RFC 4272 + discusses, it's possible for an attacker to announce an inaccurate + AS_PATH; therefore, an attacker with the ability to inject a Tunnel + Egress Endpoint sub-TLV could equally craft an AS_PATH that would + pass the validation procedures of Section 3.1.1. BGP origin + validation [RFC6811] and BGPsec [RFC8205] provide means to increase + assurance that the origins being validated have not been falsified. + + Many tunnels carry traffic that embeds a destination address that + comes from a non-global namespace. One example is MPLS VPNs. If a + tunnel crosses from one namespace to another, without the necessary + translation being performed for the embedded address(es), there + exists a risk of misdelivery of traffic. If the traffic contains + confidential data that's not otherwise protected (for example, by + end-to-end encryption), then confidential information could be + revealed. The restriction of applicability of the Tunnel + Encapsulation attribute to a well-defined scope limits the likelihood + of this occurring. See the discussion of "option b" in Section 10 + for further discussion of one such scenario. + + RFC 8402 specifies that "SR domain boundary routers MUST filter any + external traffic" ([RFC8402], Section 8.1). For these purposes, + traffic introduced into an SR domain using the Prefix-SID sub-TLV + lies within the SR domain, even though the Prefix-SIDs used by the + routers at the two ends of the tunnel may be different, as discussed + in Section 3.7. This implies that the duty to filter external + traffic extends to all routers participating in such tunnels. + +16. References + +16.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + <https://www.rfc-editor.org/info/rfc2119>. + + [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, + DOI 10.17487/RFC2474, December 1998, + <https://www.rfc-editor.org/info/rfc2474>. + + [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. + Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, + DOI 10.17487/RFC2784, March 2000, + <https://www.rfc-editor.org/info/rfc2784>. + + [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", + RFC 2890, DOI 10.17487/RFC2890, September 2000, + <https://www.rfc-editor.org/info/rfc2890>. + + [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., + Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack + Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, + <https://www.rfc-editor.org/info/rfc3032>. + + [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, + P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- + Protocol Label Switching (MPLS) Support of Differentiated + Services", RFC 3270, DOI 10.17487/RFC3270, May 2002, + <https://www.rfc-editor.org/info/rfc3270>. + + [RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed., + "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", + RFC 3931, DOI 10.17487/RFC3931, March 2005, + <https://www.rfc-editor.org/info/rfc3931>. + + [RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed., + "Encapsulating MPLS in IP or Generic Routing Encapsulation + (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005, + <https://www.rfc-editor.org/info/rfc4023>. + + [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A + Border Gateway Protocol 4 (BGP-4)", RFC 4271, + DOI 10.17487/RFC4271, January 2006, + <https://www.rfc-editor.org/info/rfc4271>. + + [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, + "Multiprotocol Extensions for BGP-4", RFC 4760, + DOI 10.17487/RFC4760, January 2007, + <https://www.rfc-editor.org/info/rfc4760>. + + [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion + Marking in MPLS", RFC 5129, DOI 10.17487/RFC5129, January + 2008, <https://www.rfc-editor.org/info/rfc5129>. + + [RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching + (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic + Class" Field", RFC 5462, DOI 10.17487/RFC5462, February + 2009, <https://www.rfc-editor.org/info/rfc5462>. + + [RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R. + Austein, "BGP Prefix Origin Validation", RFC 6811, + DOI 10.17487/RFC6811, January 2013, + <https://www.rfc-editor.org/info/rfc6811>. + + [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, + "Special-Purpose IP Address Registries", BCP 153, + RFC 6890, DOI 10.17487/RFC6890, April 2013, + <https://www.rfc-editor.org/info/rfc6890>. + + [RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger, + L., Sridhar, T., Bursell, M., and C. Wright, "Virtual + eXtensible Local Area Network (VXLAN): A Framework for + Overlaying Virtualized Layer 2 Networks over Layer 3 + Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014, + <https://www.rfc-editor.org/info/rfc7348>. + + [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. + Patel, "Revised Error Handling for BGP UPDATE Messages", + RFC 7606, DOI 10.17487/RFC7606, August 2015, + <https://www.rfc-editor.org/info/rfc7606>. + + [RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network + Virtualization Using Generic Routing Encapsulation", + RFC 7637, DOI 10.17487/RFC7637, September 2015, + <https://www.rfc-editor.org/info/rfc7637>. + + [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for + Writing an IANA Considerations Section in RFCs", BCP 26, + RFC 8126, DOI 10.17487/RFC8126, June 2017, + <https://www.rfc-editor.org/info/rfc8126>. + + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC + 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, + May 2017, <https://www.rfc-editor.org/info/rfc8174>. + + [RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah, + A., and H. Gredler, "Segment Routing Prefix Segment + Identifier Extensions for BGP", RFC 8669, + DOI 10.17487/RFC8669, December 2019, + <https://www.rfc-editor.org/info/rfc8669>. + +16.2. Informative References + + [EVPN-INTER-SUBNET] + Sajassi, A., Salam, S., Thoria, S., Drake, J. E., and J. + Rabadan, "Integrated Routing and Bridging in EVPN", Work + in Progress, Internet-Draft, draft-ietf-bess-evpn-inter- + subnet-forwarding-13, 10 February 2021, + <https://tools.ietf.org/html/draft-ietf-bess-evpn-inter- + subnet-forwarding-13>. + + [IANA-ADDRESS-FAM] + IANA, "Address Family Numbers", + <https://www.iana.org/assignments/address-family- + numbers/>. + + [IANA-BGP-EXT-COMM] + IANA, "Border Gateway Protocol (BGP) Extended + Communities", <https://www.iana.org/assignments/bgp- + extended-communities/>. + + [IANA-BGP-PARAMS] + IANA, "Border Gateway Protocol (BGP) Parameters", + <https://www.iana.org/assignments/bgp-parameters/>. + + [IANA-BGP-TUNNEL-ENCAP] + IANA, "Border Gateway Protocol (BGP) Tunnel + Encapsulation", <https://www.iana.org/assignments/bgp- + tunnel-encapsulation/>. + + [IANA-ETHERTYPES] + IANA, "IEEE 802 Numbers: ETHER TYPES", + <https://www.iana.org/assignments/ieee-802-numbers/>. + + [IANA-SAFI] + IANA, "Subsequent Address Family Identifiers (SAFI) + Parameters", + <https://www.iana.org/assignments/safi-namespace/>. + + [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", + RFC 4272, DOI 10.17487/RFC4272, January 2006, + <https://www.rfc-editor.org/info/rfc4272>. + + [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private + Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February + 2006, <https://www.rfc-editor.org/info/rfc4364>. + + [RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation + Subsequent Address Family Identifier (SAFI) and the BGP + Tunnel Encapsulation Attribute", RFC 5512, + DOI 10.17487/RFC5512, April 2009, + <https://www.rfc-editor.org/info/rfc5512>. + + [RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh + Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009, + <https://www.rfc-editor.org/info/rfc5565>. + + [RFC5566] Berger, L., White, R., and E. Rosen, "BGP IPsec Tunnel + Encapsulation Attribute", RFC 5566, DOI 10.17487/RFC5566, + June 2009, <https://www.rfc-editor.org/info/rfc5566>. + + [RFC5640] Filsfils, C., Mohapatra, P., and C. Pignataro, "Load- + Balancing for Mesh Softwires", RFC 5640, + DOI 10.17487/RFC5640, August 2009, + <https://www.rfc-editor.org/info/rfc5640>. + + [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP + Encodings and Procedures for Multicast in MPLS/BGP IP + VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012, + <https://www.rfc-editor.org/info/rfc6514>. + + [RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black, + "Encapsulating MPLS in UDP", RFC 7510, + DOI 10.17487/RFC7510, April 2015, + <https://www.rfc-editor.org/info/rfc7510>. + + [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol + Specification", RFC 8205, DOI 10.17487/RFC8205, September + 2017, <https://www.rfc-editor.org/info/rfc8205>. + + [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address + Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, + <https://www.rfc-editor.org/info/rfc8277>. + + [RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R., + Uttaro, J., and W. Henderickx, "A Network Virtualization + Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365, + DOI 10.17487/RFC8365, March 2018, + <https://www.rfc-editor.org/info/rfc8365>. + + [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., + Decraene, B., Litkowski, S., and R. Shakir, "Segment + Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, + July 2018, <https://www.rfc-editor.org/info/rfc8402>. + +Appendix A. Impact on RFC 8365 + + [RFC8365] references RFC 5512 for its definition of the BGP + Encapsulation Extended Community. That extended community is now + defined in this document, in a way consistent with its previous + definition. + + Section 6 of [RFC8365] talks about the use of the Encapsulation + Extended Community to allow Network Virtualization Edge (NVE) devices + to signal their supported encapsulations. We note that with the + introduction of this specification, the Tunnel Encapsulation + attribute can also be used for this purpose. For purposes where RFC + 8365 talks about "advertising supported encapsulations" (for example, + in the second paragraph of Section 6), encapsulations advertised + using the Tunnel Encapsulation attribute should be considered equally + with those advertised using the Encapsulation Extended Community. + + In particular, a review of Section 8.3.1 of [RFC8365] is called for, + to consider whether the introduction of the Tunnel Encapsulation + attribute creates a need for any revisions to the split-horizon + procedures. + + [RFC8365] also refers to a draft version of this specification in the + final paragraph of Section 5.1.3. That paragraph references + Section 8.2.2.2 of the draft. In this document, the correct + reference would be Section 9.2.2.2. There are no substantive + differences between the section in the referenced draft version and + that in this document. + +Acknowledgments + + This document contains text from RFC 5512, authored by Pradosh + Mohapatra and Eric Rosen. The authors of the current document wish + to thank them for their contribution. RFC 5512 itself built upon + prior work by Gargi Nalawade, Ruchi Kapoor, Dan Tappan, David Ward, + Scott Wainner, Simon Barber, Lili Wang, and Chris Metz, whom the + authors also thank for their contributions. Eric Rosen was the + principal author of earlier versions of this document. + + The authors wish to thank Lou Berger, Ron Bonica, Martin Djernaes, + John Drake, Susan Hares, Satoru Matsushima, Thomas Morin, Dhananjaya + Rao, Ravi Singh, Harish Sitaraman, Brian Trammell, Xiaohu Xu, and + Zhaohui Zhang for their review, comments, and/or helpful discussions. + Alvaro Retana provided an especially comprehensive review. + +Contributors + + Below is a list of other contributing authors in alphabetical order: + + Randy Bush + Internet Initiative Japan + 5147 Crystal Springs + Bainbridge Island, WA 98110 + United States of America + + Email: randy@psg.com + + + Robert Raszuk + Bloomberg LP + 731 Lexington Ave + New York City, NY 10022 + United States of America + + Email: robert@raszuk.net + + + Eric C. Rosen + + +Authors' Addresses + + Keyur Patel + Arrcus, Inc + 2077 Gateway Pl + San Jose, CA 95110 + United States of America + + Email: keyur@arrcus.com + + + Gunter Van de Velde + Nokia + Copernicuslaan 50 + 2018 Antwerpen + Belgium + + Email: gunter.van_de_velde@nokia.com + + + Srihari R. Sangli + Juniper Networks + + Email: ssangli@juniper.net + + + John Scudder + Juniper Networks + + Email: jgs@juniper.net |