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diff --git a/doc/rfc/rfc7795.txt b/doc/rfc/rfc7795.txt new file mode 100644 index 0000000..1f8b595 --- /dev/null +++ b/doc/rfc/rfc7795.txt @@ -0,0 +1,507 @@ + + + + + + +Internet Engineering Task Force (IETF) J. Dong +Request for Comments: 7795 H. Wang +Category: Standards Track Huawei Technologies +ISSN: 2070-1721 February 2016 + + + Pseudowire Redundancy on the Switching Provider Edge (S-PE) + +Abstract + + This document describes Multi-Segment Pseudowire (MS-PW) protection + scenarios in which pseudowire redundancy is provided on the Switching + Provider Edge (S-PE) as defined in RFC 5659. Operations of the S-PEs + that provide PW redundancy are specified in this document. Signaling + of the Preferential Forwarding status as defined in RFCs 6870 and + 6478 is reused. This document does not require any change to the + Terminating Provider Edges (T-PEs) of MS-PW. + +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/rfc7795. + +Copyright Notice + + Copyright (c) 2016 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. + + + + + +Dong & Wang Standards Track [Page 1] + +RFC 7795 PW Redundancy on S-PE February 2016 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 + 2. Typical Scenarios of PW Redundancy on S-PE . . . . . . . . . 3 + 2.1. MS-PW Redundancy on S-PE . . . . . . . . . . . . . . . . 3 + 2.2. MS-PW Redundancy on S-PE with S-PE Protection . . . . . . 4 + 3. S-PE Operations . . . . . . . . . . . . . . . . . . . . . . . 4 + 4. Applications of PW Redundancy on S-PE . . . . . . . . . . . . 5 + 4.1. Applications in Scenario 1 . . . . . . . . . . . . . . . 5 + 4.2. Applications in Scenario 2 . . . . . . . . . . . . . . . 6 + 5. VCCV Considerations . . . . . . . . . . . . . . . . . . . . . 7 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 + 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 + 7.2. Informative References . . . . . . . . . . . . . . . . . 8 + Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 + +1. Introduction + + [RFC6718] describes the framework and requirements for pseudowire + (PW) redundancy, and [RFC6870] specifies a PW redundancy mechanism + for scenarios where a set of redundant PWs are configured between + Provider Edge (PE) nodes in Single-Segment Pseudowire (SS-PW) + [RFC3985] applications, or between Terminating Provider Edge (T-PE) + nodes in Multi-Segment Pseudowire (MS-PW) [RFC5659] applications. + + In some MS-PW scenarios, there are benefits of providing PW + redundancy on Switching Provider Edges (S-PEs), such as reducing the + burden on the access T-PE nodes and enabling faster protection + switching compared to the end-to-end MS-PW protection mechanisms. + + This document describes some scenarios in which PW redundancy is + provided on S-PEs and specifies the operations of the S-PEs. The + S-PEs connect to the neighboring T-PEs or S-PEs with PW segments. + For the S-PE that provides PW redundancy for an MS-PW, there is a + single PW segment on one side, which is called the single-homed side, + and there are multiple PW segments on the other side, which is called + the multi-homed side. The scenario in which the S-PE has two multi- + homed sides is out of scope. Signaling of the Preferential + Forwarding status as defined in [RFC6870] and [RFC6478] is reused. + This document does not require any change to the T-PEs of MS-PW. + + 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 RFC 2119 [RFC2119]. + + + + + +Dong & Wang Standards Track [Page 2] + +RFC 7795 PW Redundancy on S-PE February 2016 + + +2. Typical Scenarios of PW Redundancy on S-PE + + In some MS-PW deployment scenarios, there are benefits of providing + PW redundancy on S-PEs. This section describes typical scenarios of + PW redundancy on S-PE. + +2.1. MS-PW Redundancy on S-PE + + +-----+ AC + +---+ +-----+ | | | +---+ + | | | |------|T-PE2|-----| | + | | AC +-----+ | ..PW-Seg2.......| | | + | | | |....PW-Seg1..... | +-----+ | | + |CE1|-----|T-PE1|------|S-PE1| |CE2| + | | | | | . | +-----+ | | + | | +-----+ | ..PW-Seg3.......| | | + | | | |------|T-PE3|-----| | + +---+ +-----+ | | | +---+ + +-----+ AC + + Figure 1: MS-PW Redundancy on S-PE + + As illustrated in Figure 1, Customer Edge (CE) node CE1 is connected + to T-PE1 while CE2 is dual-homed to T-PE2 and T-PE3. T-PE1 is + connected to S-PE1 only, and S-PE1 is connected to both T-PE2 and + T-PE3. The MS-PW is switched on S-PE1, and PW segments PW-Seg2 and + PW-Seg3 provide resiliency on S-PE1 for the failure of T-PE2, T-PE3, + or the connected Attachment Circuits (ACs). PW-Seg2 is selected as + the primary PW segment, and PW-Seg3 is the secondary PW segment. + + MS-PW redundancy on S-PE is beneficial for the scenario in Figure 1 + since T-PE1 as an access node may not support PW redundancy. + Besides, with PW redundancy on S-PE, the number of PW segments + required between T-PE1 and S-PE1 is only half of the number of PW + segments needed when end-to-end MS-PW redundancy is used. In + addition, in this scenario, PW redundancy on S-PE could provide + faster protection switching, compared with end-to-end protection + switching of MS-PW. + + + + + + + + + + + + + +Dong & Wang Standards Track [Page 3] + +RFC 7795 PW Redundancy on S-PE February 2016 + + +2.2. MS-PW Redundancy on S-PE with S-PE Protection + + +---+ +-----+ +-----+ +-----+ + | | | | | | | | + | | AC |......PW1-Seg1......PW1-Seg2........| + | | | | . | | . | | | + |CE1|-----|T-PE1|------|S-PE1|-----------|T-PE2| AC + | | | . | | . | PW1-Seg3 | | | +---+ + | | | . | | ......... ......|-----| | + | | | . | | | . .| | | | + +---+ +---.-+ +-----+ . . +-----+ | | + |. . . |CE2| + |. .. | | + |. +-----+ . . +-----+ | | + |. | | . .| |-----| | + |...PW2-Seg1.......... ......| | +---+ + | | . | PW2-Seg2 | | AC + ----------|S-PE2|-----------|T-PE3| + | . | | | + | .....PW2-Seg3........| + | | | | + +-----+ +-----+ + + Figure 2: MS-PW Redundancy on S-PE with S-PE Protection + + As illustrated in Figure 2, CE1 is connected to T-PE1 while CE2 is + dual-homed to T-PE2 and T-PE3. T-PE1 is connected to both S-PE1 and + S-PE2, and both S-PE1 and S-PE2 are connected to both T-PE2 and + T-PE3. There are two MS-PWs that are switched at S-PE1 and S-PE2, + respectively, to provide S-PE node protection. For PW1, S-PE1 + provides resiliency using PW1-Seg2 and PW1-Seg3. For PW2, S-PE2 + provides resiliency using PW2-Seg2 and PW2-Seg3. PW1 is the primary + MS-PW, and PW1-Seg2 between S-PE1 and T-PE2 is the primary PW + segment. PW2 is the secondary MS-PW. + + MS-PW redundancy on S-PE is beneficial for this scenario because it + reduces the number of end-to-end MS-PWs required for both T-PE and + S-PE protection. In addition, PW redundancy on S-PE could provide + faster protection switching, compared with end-to-end protection + switching of MS-PW. + +3. S-PE Operations + + For an S-PE that provides PW redundancy for MS-PW, it is important to + advertise the proper preferential forwarding status to the PW + segments on both sides and perform protection switching according to + the received status information. Note that when PW redundancy for + MS-PW is provided on S-PE, the optional S-PE Bypass mode as defined + + + +Dong & Wang Standards Track [Page 4] + +RFC 7795 PW Redundancy on S-PE February 2016 + + + in [RFC6478] MUST NOT be used; otherwise, the S-PE will not receive + the PW status messages originated by T-PEs. This section specifies + the operations of S-PEs on which PW redundancy is provisioned. This + section does not make any change to the T-PEs of MS-PW. + + The S-PEs connect to the neighboring T-PEs or other S-PEs on two + sides with PW segments. For the S-PE that provides PW redundancy for + an MS-PW, on one side there is a single PW segment, which is called + the single-homed side, and on the other side there are multiple PW + segments, which is called the multi-homed side. The scenario in + which the S-PE has two multi-homed sides is out of scope. + + The S-PE that provides PW redundancy MUST work in Slave mode for the + single-homed side, and MUST work in Independent mode for the multi- + homed side. Consequently, the T-PE on the single-homed side MUST + work in the Master mode, and the T-PEs on the multi-homed side MUST + work in the Independent mode. The signaling of the Preferential + Forwarding bit as defined in [RFC6870] and [RFC6478] is reused. + + The S-PE MUST pass the Preferential Forwarding status received from + the single-homed side unchanged to all the PW segments on the multi- + homed side. The S-PE MUST advertise the Standby Preferential + Forwarding status to the single-homed side if it receives Standby + status from all the PW segments on the multi-homed side, and it MUST + advertise the Active Preferential Forwarding status to the single- + homed side if it receives Active status from any of the PW segments + on the multi-homed side. For the single-homed side, the active PW + segment is determined by the T-PE on this side, which works in the + Master mode. On the multi-homed side, since both the S-PE and T-PEs + work in the Independent mode, the PW segment which has both the local + and remote Up/Down status as Up and both the local and remote + Preferential Forwarding status as Active MUST be selected for traffic + forwarding. When a switchover happens on the S-PE, if the S-PE + supports the SP-PE TLV processing as defined in [RFC6073], it SHOULD + advertise the updated SP-PE TLVs by sending a Label Mapping message + to the T-PEs. + +4. Applications of PW Redundancy on S-PE + +4.1. Applications in Scenario 1 + + For the scenario in Figure 1, assume the AC from CE2 to T-PE2 is + active. In normal operation, S-PE1 would receive the Active + Preferential Forwarding status bit on the single-homed side from + T-PE1, then it would advertise the Active Preferential Forwarding + status bit on both PW-Seg2 and PW-Seg3. T-PE2 and T-PE3 would + advertise the Active and Standby Preferential Forwarding status bit + to S-PE1, respectively, reflecting the forwarding state of the two + + + +Dong & Wang Standards Track [Page 5] + +RFC 7795 PW Redundancy on S-PE February 2016 + + + ACs connected to CE2. By matching the local and remote Up/Down + status and Preferential Forwarding status, PW-Seg2 would be used for + traffic forwarding. + + On failure of the AC between CE2 and T-PE2, the forwarding state of + AC on T-PE3 is changed to Active. T-PE3 then advertises the Active + Preferential Forwarding status to S-PE1, and T-PE2 would advertise a + PW status Notification message to S-PE1, indicating that the AC + between CE2 and T-PE2 is down. S-PE1 would perform the switchover + according to the updated local and remote Preferential Forwarding + status and the status of "Pseudowire forwarding", and select PW-Seg3 + as the new PW segment for traffic forwarding. Since S-PE1 still + connects to an Active PW segment on the multi-homed side, it will not + advertise any change of the PW status to T-PE1. If S-PE1 supports + the SP-PE TLV processing as defined in [RFC6073], it would advertise + the updated SP-PE TLVs by sending a Label Mapping message to T-PE1. + +4.2. Applications in Scenario 2 + + For the scenario of Figure 2, assume the AC from CE2 to T-PE2 is + active. T-PE1 works in Master mode and it would advertise the Active + and Standby Preferential Forwarding status bit to S-PE1 and S-PE2 + respectively according to configuration. According to the received + Preferential Forwarding status bit, S-PE1 would advertise the Active + Preferential Forwarding status bit to both T-PE2 and T-PE3, and S-PE2 + would advertise the Standby Preferential Forwarding status bit to + both T-PE2 and T-PE3. T-PE2 would advertise the Active Preferential + Forwarding status bit to both S-PE1 and S-PE2, and T-PE3 would + advertise the Standby Preferential Forwarding status bit to both + S-PE1 and S-PE2, reflecting the forwarding state of the two ACs + connected to CE2. By matching the local and remote Up/Down Status + and Preferential Forwarding status, PW1-Seg2 from S-PE1 to T-PE2 + would be used for traffic forwarding. Since S-PE1 connects to the + Active PW segment on the multi-homed side, it would advertise the + Active Preferential Forwarding status bit to T-PE1, and S-PE2 would + advertise the Standby Preferential Forwarding status bit to T-PE1 + because it does not have any Active PW segment on the multi-homed + side. + + On failure of the AC between CE2 and T-PE2, the forwarding state of + AC on T-PE3 is changed to Active. T-PE3 would then advertise the + Active Preferential Forwarding status bit to both S-PE1 and S-PE2, + and T-PE2 would advertise a PW status Notification message to both + S-PE1 and S-PE2, indicating that the AC between CE2 and T-PE2 is + down. S-PE1 would perform the switchover according to the updated + local and remote Preferential Forwarding status and the status of + "Pseudowire forwarding", and select PW1-Seg3 for traffic forwarding. + Since S-PE1 still has an Active PW segment on the multi-homed side, + + + +Dong & Wang Standards Track [Page 6] + +RFC 7795 PW Redundancy on S-PE February 2016 + + + it would not advertise any change of the PW status to T-PE1. If + S-PE1 supports the SP-PE TLV processing as defined in [RFC6073], it + would advertise the updated SP-PE TLVs by sending a Label Mapping + message to T-PE1. + + If S-PE1 fails, T-PE1 would notice this through some detection + mechanism and then advertise the Active Preferential Forwarding + status bit to S-PE2, and PW2-Seg1 would be selected by T-PE1 for + traffic forwarding. On receipt of the newly changed Preferential + Forwarding status, S-PE2 would advertise the Active Preferential + Forwarding status to both T-PE2 and T-PE3. T-PE2 and T-PE3 would + also notice the failure of S-PE1 by some detection mechanism. Then + by matching the local and remote Up/Down and Preferential Forwarding + status, PW2-Seg2 would be selected for traffic forwarding. + +5. VCCV Considerations + + For PW Virtual Circuit Connectivity Verification (VCCV) [RFC5085], + the Control Channel (CC) type 1 "PW ACH" can be used with the S-PE + redundancy mechanism. VCCV CC type 2 "Router Alert Label" is not + supported for MS-PW as specified in [RFC6073]. If VCCV CC type 3 + "TTL Expiry" is to be used, the PW label TTL MUST be set to the + appropriate value to reach the target PE. The hop count from one + T-PE to the target PE can be obtained via SP-PE TLVs, through MS-PW + path trace, or based on management-plane information. + +6. Security Considerations + + Since PW redundancy is provided on the S-PE nodes of MS-PWs, it is + important that the security mechanisms as defined in [RFC4447], + [RFC6073], and [RFC6478] be implemented to ensure that the S-PE nodes + and the messages sent and received by the S-PE nodes are not + compromised. + +7. References + +7.1. 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, + <http://www.rfc-editor.org/info/rfc2119>. + + [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, + DOI 10.17487/RFC4447, April 2006, + <http://www.rfc-editor.org/info/rfc4447>. + + + +Dong & Wang Standards Track [Page 7] + +RFC 7795 PW Redundancy on S-PE February 2016 + + + [RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. + Aissaoui, "Segmented Pseudowire", RFC 6073, + DOI 10.17487/RFC6073, January 2011, + <http://www.rfc-editor.org/info/rfc6073>. + + [RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci, + "Pseudowire Status for Static Pseudowires", RFC 6478, + DOI 10.17487/RFC6478, May 2012, + <http://www.rfc-editor.org/info/rfc6478>. + + [RFC6870] Muley, P., Ed. and M. Aissaoui, Ed., "Pseudowire + Preferential Forwarding Status Bit", RFC 6870, + DOI 10.17487/RFC6870, February 2013, + <http://www.rfc-editor.org/info/rfc6870>. + +7.2. Informative References + + [RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation + Edge-to-Edge (PWE3) Architecture", RFC 3985, + DOI 10.17487/RFC3985, March 2005, + <http://www.rfc-editor.org/info/rfc3985>. + + [RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual + Circuit Connectivity Verification (VCCV): A Control + Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, + December 2007, <http://www.rfc-editor.org/info/rfc5085>. + + [RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi- + Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, + DOI 10.17487/RFC5659, October 2009, + <http://www.rfc-editor.org/info/rfc5659>. + + [RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire + Redundancy", RFC 6718, DOI 10.17487/RFC6718, August 2012, + <http://www.rfc-editor.org/info/rfc6718>. + + + + + + + + + + + + + + + + +Dong & Wang Standards Track [Page 8] + +RFC 7795 PW Redundancy on S-PE February 2016 + + +Acknowledgements + + The authors would like to thank Mach Chen, Lizhong Jin, Mustapha + Aissaoui, Luca Martini, Matthew Bocci, and Stewart Bryant for their + valuable comments and discussions. + +Authors' Addresses + + Jie Dong + Huawei Technologies + Huawei Building, No.156 Beiqing Rd. + Beijing 100095 + China + + Email: jie.dong@huawei.com + + + Haibo Wang + Huawei Technologies + Huawei Building, No.156 Beiqing Rd. + Beijing 100095 + China + + Email: rainsword.wang@huawei.com + + + + + + + + + + + + + + + + + + + + + + + + + + + +Dong & Wang Standards Track [Page 9] + |