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diff --git a/doc/rfc/rfc5884.txt b/doc/rfc/rfc5884.txt new file mode 100644 index 0000000..9073bd2 --- /dev/null +++ b/doc/rfc/rfc5884.txt @@ -0,0 +1,675 @@ + + + + + + +Internet Engineering Task Force (IETF) R. Aggarwal +Request for Comments: 5884 K. Kompella +Updates: 1122 Juniper Networks +Category: Standards Track T. Nadeau +ISSN: 2070-1721 BT + G. Swallow + Cisco Systems, Inc. + June 2010 + + + Bidirectional Forwarding Detection (BFD) + for MPLS Label Switched Paths (LSPs) + +Abstract + + One desirable application of Bidirectional Forwarding Detection (BFD) + is to detect a Multiprotocol Label Switching (MPLS) Label Switched + Path (LSP) data plane failure. LSP Ping is an existing mechanism for + detecting MPLS data plane failures and for verifying the MPLS LSP + data plane against the control plane. BFD can be used for the + former, but not for the latter. However, the control plane + processing required for BFD Control packets is relatively smaller + than the processing required for LSP Ping messages. A combination of + LSP Ping and BFD can be used to provide faster data plane failure + detection and/or make it possible to provide such detection on a + greater number of LSPs. This document describes the applicability of + BFD in relation to LSP Ping for this application. It also describes + procedures for using BFD in this environment. + +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 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5884. + + + + + + + + + +Aggarwal, et al. Standards Track [Page 1] + +RFC 5884 BFD for MPLS LSPs June 2010 + + +Copyright Notice + + Copyright (c) 2010 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 + (http://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. + + This document may contain material from IETF Documents or IETF + Contributions published or made publicly available before November + 10, 2008. The person(s) controlling the copyright in some of this + material may not have granted the IETF Trust the right to allow + modifications of such material outside the IETF Standards Process. + Without obtaining an adequate license from the person(s) controlling + the copyright in such materials, this document may not be modified + outside the IETF Standards Process, and derivative works of it may + not be created outside the IETF Standards Process, except to format + it for publication as an RFC or to translate it into languages other + than English. + +Table of Contents + + 1. Introduction ....................................................3 + 2. Specification of Requirements ...................................3 + 3. Applicability ...................................................3 + 3.1. BFD for MPLS LSPs: Motivation ..............................3 + 3.2. Using BFD in Conjunction with LSP Ping .....................5 + 4. Theory of Operation .............................................6 + 5. Initialization and Demultiplexing ...............................7 + 6. Session Establishment ...........................................7 + 6.1. BFD Discriminator TLV in LSP Ping ..........................8 + 7. Encapsulation ...................................................8 + 8. Security Considerations .........................................9 + 9. IANA Considerations ............................................10 + 10. Acknowledgments ...............................................10 + 11. References ....................................................10 + 11.1. Normative References .....................................10 + 11.2. Informative References ...................................10 + + + + + + +Aggarwal, et al. Standards Track [Page 2] + +RFC 5884 BFD for MPLS LSPs June 2010 + + +1. Introduction + + One desirable application of Bidirectional Forwarding Detection (BFD) + is to track the liveness of a Multiprotocol Label Switching (MPLS) + Label Switched Path (LSP). In particular, BFD can be used to detect + a data plane failure in the forwarding path of an MPLS LSP. LSP Ping + [RFC4379] is an existing mechanism for detecting MPLS LSP data plane + failures and for verifying the MPLS LSP data plane against the + control plane. This document describes the applicability of BFD in + relation to LSP Ping for detecting MPLS LSP data plane failures. It + also describes procedures for using BFD for detecting MPLS LSP data + plane failures. + +2. Specification of Requirements + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + +3. Applicability + + In the event of an MPLS LSP failing to deliver data traffic, it may + not always be possible to detect the failure using the MPLS control + plane. For instance, the control plane of the MPLS LSP may be + functional while the data plane may be mis-forwarding or dropping + data. Hence, there is a need for a mechanism to detect a data plane + failure in the MPLS LSP path [RFC4377]. + +3.1. BFD for MPLS LSPs: Motivation + + LSP Ping described in [RFC4379] is an existing mechanism for + detecting an MPLS LSP data plane failure. In addition, LSP Ping also + provides a mechanism for verifying the MPLS control plane against the + data plane. This is done by ensuring that the LSP is mapped to the + same Forwarding Equivalence Class (FEC), at the egress, as the + ingress. + + BFD cannot be used for verifying the MPLS control plane against the + data plane. However, BFD can be used to detect a data plane failure + in the forwarding path of an MPLS LSP. The LSP may be associated + with any of the following FECs: + + a) Resource Reservation Protocol (RSVP) LSP_Tunnel IPv4/IPv6 + Session [RFC3209] + + b) Label Distribution Protocol (LDP) IPv4/IPv6 prefix [RFC5036] + + c) Virtual Private Network (VPN) IPv4/IPv6 prefix [RFC4364] + + + +Aggarwal, et al. Standards Track [Page 3] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + d) Layer 2 VPN [L2-VPN] + + e) Pseudowires based on PWid FEC and Generalized PWid FEC + [RFC4447] + + f) Border Gateway Protocol (BGP) labeled prefixes [RFC3107] + + LSP Ping includes extensive control plane verification. BFD, on the + other hand, was designed as a lightweight means of testing only the + data plane. As a result, LSP Ping is computationally more expensive + than BFD for detecting MPLS LSP data plane faults. BFD is also more + suitable for being implemented in hardware or firmware due to its + fixed packet format. Thus, the use of BFD for detecting MPLS LSP + data plane faults has the following advantages: + + a) Support for fault detection for greater number of LSPs. + + b) Fast detection. Detection with sub-second granularity is + considered as fast detection. LSP Ping is intended to be used + in an environment where fault detection messages are exchanged, + either for diagnostic purposes or for infrequent periodic fault + detection, in the order of tens of seconds or minutes. Hence, + it is not appropriate for fast detection. BFD, on the other + hand, is designed for sub-second fault detection intervals. + Following are some potential cases when fast detection may be + desirable for MPLS LSPs: + + 1. In the case of a bypass LSP used for a facility-based link + or node protection [RFC4090]. In this case, the bypass LSP + is essentially being used as an alternate link to protect + one or more LSPs. It represents an aggregate and is used to + carry data traffic belonging to one or more LSPs, when the + link or the node being protected fails. Hence, fast failure + detection of the bypass LSP may be desirable particularly in + the event of link or node failure when the data traffic is + moved to the bypass LSP. + + 2. MPLS Pseudowires (PWs). Fast detection may be desired for + MPLS PWs depending on i) the model used to layer the MPLS + network with the Layer 2 network, and ii) the service that + the PW is emulating. For a non-overlay model between the + Layer 2 network and the MPLS network, the provider may rely + on PW fault detection to provide service status to the end- + systems. Also, in that case, interworking scenarios such as + ATM/Frame Relay interworking may force periodic PW fault + detection messages. Depending on the requirements of the + service that the MPLS PW is emulating, fast failure + detection may be desirable. + + + +Aggarwal, et al. Standards Track [Page 4] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + There may be other potential cases where fast failure detection is + desired for MPLS LSPs. + +3.2. Using BFD in Conjunction with LSP Ping + + BFD can be used for MPLS LSP data plane fault detection. However, it + does not have all the functionality of LSP Ping. In particular, it + cannot be used for verifying the control plane against the data + plane. LSP Ping performs the following functions that are outside + the scope of BFD: + + a) Association of an LSP Ping Echo request message with a FEC. In + the case of Penultimate Hop Popping (PHP) or when the egress + Label Switching Router (LSR) distributes an explicit null label + to the penultimate hop router, for a single label stack LSP, + the only way to associate a fault detection message with a FEC + is by carrying the FEC in the message. LSP Ping provides this + functionality. Next-hop label allocation also makes it + necessary to carry the FEC in the fault detection message as + the label alone is not sufficient to identify the LSP being + verified. In addition, presence of the FEC in the Echo request + message makes it possible to verify the control plane against + the data plane at the egress LSR. + + b) Equal Cost Multi-Path (ECMP) considerations. LSP Ping + traceroute makes it possible to probe multiple alternate paths + for LDP IP FECs. + + c) Traceroute. LSP Ping supports traceroute for a FEC and it can + be used for fault isolation. + + Hence, BFD is used in conjunction with LSP Ping for MPLS LSP fault + detection: + + i) LSP Ping is used for bootstrapping the BFD session as described + later in this document. + + ii) BFD is used to exchange fault detection (i.e., BFD session) + packets at the required detection interval. + + iii) LSP Ping is used to periodically verify the control plane + against the data plane by ensuring that the LSP is mapped to + the same FEC, at the egress, as the ingress. + + + + + + + + +Aggarwal, et al. Standards Track [Page 5] + +RFC 5884 BFD for MPLS LSPs June 2010 + + +4. Theory of Operation + + To use BFD for fault detection on an MPLS LSP, a BFD session MUST be + established for that particular MPLS LSP. BFD Control packets MUST + be sent along the same data path as the LSP being verified and are + processed by the BFD processing module of the egress LSR. If the LSP + is associated with multiple FECs, a BFD session SHOULD be established + for each FEC. For instance, this may happen in the case of next-hop + label allocation. Hence, the operation is conceptually similar to + the data plane fault detection procedures of LSP Ping. + + If MPLS fast-reroute is being used for the MPLS LSP, the use of BFD + for fault detection can result in false fault detections if the BFD + fault detection interval is less than the MPLS fast-reroute + switchover time. When MPLS fast-reroute is triggered because of a + link or node failure, BFD Control packets will be dropped until + traffic is switched on to the backup LSP. If the time taken to + perform the switchover exceeds the BFD fault detection interval, a + fault will be declared even though the MPLS LSP is being locally + repaired. To avoid this, the BFD fault detection interval should be + greater than the fast-reroute switchover time. An implementation + SHOULD provide configuration options to control the BFD fault + detection interval. + + If there are multiple alternate paths from an ingress LSR to an + egress LSR for an LDP IP FEC, LSP Ping traceroute MAY be used to + determine each of these alternate paths. A BFD session SHOULD be + established for each alternate path that is discovered. + + Periodic LSP Ping Echo request messages SHOULD be sent by the ingress + LSR to the egress LSR along the same data path as the LSP. This is + to periodically verify the control plane against the data plane by + ensuring that the LSP is mapped to the same FEC, at the egress, as + the ingress. The rate of generation of these LSP Ping Echo request + messages SHOULD be significantly less than the rate of generation of + the BFD Control packets. An implementation MAY provide configuration + options to control the rate of generation of the periodic LSP Ping + Echo request messages. + + To enable fault detection procedures specified in this document, for + a particular MPLS LSP, this document requires the ingress and egress + LSRs to be configured. This includes configuration for supporting + BFD and LSP Ping as specified in this document. It also includes + configuration that enables the ingress LSR to determine the method + used by the egress LSR to identify Operations, Administration, and + Maintenance (OAM) packets, e.g., whether the Time to Live (TTL) of + the innermost MPLS label needs to be set to 1 to enable the egress + + + + +Aggarwal, et al. Standards Track [Page 6] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + LSR to identify the OAM packet. For fault detection for MPLS PWs, + this document assumes that the PW control channel type [RFC5085] is + configured and the support of LSP Ping is also configured. + +5. Initialization and Demultiplexing + + A BFD session may be established for a FEC associated with an MPLS + LSP. As described above, in the case of PHP or when the egress LSR + distributes an explicit null label to the penultimate hop router, or + next-hop label allocation, the BFD Control packet received by the + egress LSR does not contain sufficient information to associate it + with a BFD session. Hence, the demultiplexing MUST be done using the + remote discriminator field in the received BFD Control packet. The + exchange of BFD discriminators for this purpose is described in the + next section. + +6. Session Establishment + + A BFD session is bootstrapped using LSP Ping. This specification + describes procedures only for BFD asynchronous mode. BFD demand mode + is outside the scope of this specification. Further, the use of the + Echo function is outside the scope of this specification. The + initiation of fault detection for a particular <MPLS LSP, FEC> + combination results in the exchange of LSP Ping Echo request and Echo + reply packets, in the ping mode, between the ingress and egress LSRs + for that <MPLS LSP, FEC>. To establish a BFD session, an LSP Ping + Echo request message MUST carry the local discriminator assigned by + the ingress LSR for the BFD session. This MUST subsequently be used + as the My Discriminator field in the BFD session packets sent by the + ingress LSR. + + On receipt of the LSP Ping Echo request message, the egress LSR MUST + send a BFD Control packet to the ingress LSR, if the validation of + the FEC in the LSP Ping Echo request message succeeds. This BFD + Control packet MUST set the Your Discriminator field to the + discriminator received from the ingress LSR in the LSP Ping Echo + request message. The egress LSR MAY respond with an LSP Ping Echo + reply message that carries the local discriminator assigned by it for + the BFD session. The local discriminator assigned by the egress LSR + MUST be used as the My Discriminator field in the BFD session packets + sent by the egress LSR. + + The ingress LSR follows the procedures in [BFD] to send BFD Control + packets to the egress LSR in response to the BFD Control packets + received from the egress LSR. The BFD Control packets from the + ingress to the egress LSR MUST set the local discriminator of the + egress LSR, in the Your Discriminator field. The egress LSR + demultiplexes the BFD session based on the received Your + + + +Aggarwal, et al. Standards Track [Page 7] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + Discriminator field. As mentioned above, the egress LSR MUST send + Control packets to the ingress LSR with the Your Discriminator field + set to the local discriminator of the ingress LSR. The ingress LSR + uses this to demultiplex the BFD session. + +6.1. BFD Discriminator TLV in LSP Ping + + LSP Ping Echo request and Echo reply messages carry a BFD + discriminator TLV for the purpose of session establishment as + described above. IANA has assigned a type value of 15 to this TLV. + This TLV has a length of 4. The value contains the 4-byte local + discriminator that the LSR, sending the LSP Ping message, associates + with the BFD session. + + If the BFD session is not in UP state, the periodic LSP Ping Echo + request messages MUST include the BFD Discriminator TLV. + +7. Encapsulation + + BFD Control packets sent by the ingress LSR MUST be encapsulated in + the MPLS label stack that corresponds to the FEC for which fault + detection is being performed. If the label stack has a depth greater + than one, the TTL of the inner MPLS label MAY be set to 1. This may + be necessary for certain FECs to enable the egress LSR's control + plane to receive the packet [RFC4379]. For MPLS PWs, alternatively, + the presence of a fault detection message may be indicated by setting + a bit in the control word [RFC5085]. + + The BFD Control packet sent by the ingress LSR MUST be a UDP packet + with a well-known destination port 3784 [BFD-IP] and a source port + assigned by the sender as per the procedures in [BFD-IP]. The source + IP address is a routable address of the sender. The destination IP + address MUST be randomly chosen from the 127/8 range for IPv4 and + from the 0:0:0:0:0:FFFF:7F00/104 range for IPv6 with the following + exception. If the FEC is an LDP IP FEC, the ingress LSR may discover + multiple alternate paths to the egress LSR for this FEC using LSP + Ping traceroute. In this case, the destination IP address, used in a + BFD session established for one such alternate path, is the address + in the 127/8 range for IPv4 or 0:0:0:0:0:FFFF:7F00/104 range for IPv6 + discovered by LSP Ping traceroute [RFC4379] to exercise that + particular alternate path. + + The motivation for using the address range 127/8 is the same as + specified in Section 2.1 of [RFC4379]. This is an exception to the + behavior defined in [RFC1122]. + + The IP TTL or hop limit MUST be set to 1 [RFC4379]. + + + + +Aggarwal, et al. Standards Track [Page 8] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + BFD Control packets sent by the egress LSR are UDP packets. The + source IP address is a routable address of the replier. + + The BFD Control packet sent by the egress LSR to the ingress LSR MAY + be routed based on the destination IP address as per the procedures + in [BFD-MHOP]. If this is the case, the destination IP address MUST + be set to the source IP address of the LSP Ping Echo request message, + received by the egress LSR from the ingress LSR. + + Or the BFD Control packet sent by the egress LSR to the ingress LSR + MAY be encapsulated in an MPLS label stack. In this case, the + presence of the fault detection message is indicated as described + above. This may be the case if the FEC for which the fault detection + is being performed corresponds to a bidirectional LSP or an MPLS PW. + This may also be the case when there is a return LSP from the egress + LSR to the ingress LSR. In this case, the destination IP address + MUST be randomly chosen from the 127/8 range for IPv4 and from the + 0:0:0:0:0:FFFF:7F00/104 range for IPv6. + + The BFD Control packet sent by the egress LSR MUST have a well-known + destination port 4784, if it is routed [BFD-MHOP], or it MUST have a + well-known destination port 3784 [BFD-IP] if it is encapsulated in a + MPLS label stack. The source port MUST be assigned by the egress LSR + as per the procedures in [BFD-IP]. + + Note that once the BFD session for the MPLS LSP is UP, either end of + the BFD session MUST NOT change the source IP address and the local + discriminator values of the BFD Control packets it generates, unless + it first brings down the session. This implies that an LSR MUST + ignore BFD packets for a given session, demultiplexed using the + received Your Discriminator field, if the session is in UP state and + if the My Discriminator or the Source IP address fields of the + received packet do not match the values associated with the session. + +8. Security Considerations + + Security considerations discussed in [BFD], [BFD-MHOP], and [RFC4379] + apply to this document. For BFD Control packets sent by the ingress + LSR or when the BFD Control packet sent by the egress LSR are + encapsulated in an MPLS label stack, MPLS security considerations + apply. These are discussed in [MPLS-SEC]. When BFD Control packets + sent by the egress LSR are routed, the authentication considerations + discussed in [BFD-MHOP] should be followed. + + + + + + + + +Aggarwal, et al. Standards Track [Page 9] + +RFC 5884 BFD for MPLS LSPs June 2010 + + +9. IANA Considerations + + This document introduces a BFD discriminator TLV in LSP Ping. The + BFD Discriminator has been assigned a value of 15 from the LSP Ping + TLVs and sub-TLVs registry maintained by IANA. + +10. Acknowledgments + + We would like to thank Yakov Rekhter, Dave Katz, and Ina Minei for + contributing to the discussions that formed the basis of this + document and for their comments. Thanks to Dimitri Papadimitriou for + his comments and review. Thanks to Carlos Pignataro for his comments + and review. + +11. References + +11.1. Normative References + + [BFD] Katz, D. and D. Ward, "Bidirectional Forwarding + Detection", RFC 5880, June 2010. + + [BFD-IP] Katz, D. and D. Ward, "Bidirectional Forwarding Detection + (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June + 2010. + + [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol + Label Switched (MPLS) Data Plane Failures", RFC 4379, + February 2006. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - + Communication Layers", STD 3, RFC 1122, October 1989. + +11.2. Informative References + + [BFD-MHOP] Katz, D. and D. Ward, "Bidirectional Forwarding Detection + (BFD) for Multihop Paths", RFC 5883, June 2010. + + [RFC5085] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire + Virtual Circuit Connectivity Verification (VCCV): A + Control Channel for Pseudowires", RFC 5085, December 2007. + + [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., + and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP + Tunnels", RFC 3209, December 2001. + + + + +Aggarwal, et al. Standards Track [Page 10] + +RFC 5884 BFD for MPLS LSPs June 2010 + + + [RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast + Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, + May 2005. + + [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., + "LDP Specification", RFC 5036, October 2007. + + [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private + Networks (VPNs)", RFC 4364, February 2006. + + [L2-VPN] Kompella, K., Leelanivas, M., Vohra, Q., Achirica, J., + Bonica, R., Cooper, D., Liljenstolpe, C., Metz, E., Ould- + Brahim, H., Sargor, C., Shah, H., Srinivasan, and Z. + Zhang, "Layer 2 VPNs Over Tunnels", Work in Progress, + February 2003. + + [RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and + G. Heron, "Pseudowire Setup and Maintenance Using the + Label Distribution Protocol (LDP)", RFC 4447, April 2006. + + [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in + BGP-4", RFC 3107, May 2001. + + [RFC4377] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S. + Matsushima, "Operations and Management (OAM) Requirements + for Multi-Protocol Label Switched (MPLS) Networks", RFC + 4377, February 2006. + + [MPLS-SEC] Fang, L., Ed., "Security Framework for MPLS and GMPLS + Networks", Work in Progress, October 2009. + + + + + + + + + + + + + + + + + + + + + +Aggarwal, et al. Standards Track [Page 11] + +RFC 5884 BFD for MPLS LSPs June 2010 + + +Authors' Addresses + + Rahul Aggarwal + Juniper Networks + 1194 N. Mathilda Ave. + Sunnyvale, CA 94089 + USA + + EMail: rahul@juniper.net + + + Kireeti Kompella + Juniper Networks + 1194 N. Mathilda Ave. + Sunnyvale, CA 94089 + USA + + EMail: kireeti@juniper.net + + + Thomas D. Nadeau + BT + BT Centre + 81 Newgate Street + London EC1A 7AJ + UK + + EMail: tom.nadeau@bt.com + + + George Swallow + Cisco Systems, Inc. + 300 Beaver Brook Road + Boxborough, MA 01719 + USA + + EMail: swallow@cisco.com + + + + + + + + + + + + + + +Aggarwal, et al. Standards Track [Page 12] + |