SRv6 SID Bypass Functions
draft-chen-bess-srv6-service-bypass-sid-00

Abstract

This document introduces the SRv6 SID Bypass Functions to enhance reliability and prevent traffic loop in fast reroute(FRR) scenario.

Requirements Language

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.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on January 14, 2021.

Copyright Notice

Copyright (c) 2020 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
• 2. SRv6 SID Bypass Functions
• 2.1. End.DX2L
• 3. Control Plane Processing
• 4. Data Plane Processing
• 5. IANA Considerations
• 6. Security Considerations
• 7. Contributors
• 8. Acknowledgements
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

In SRv6 EVPN VPWS all-active scenario, a router or switch (CE1) is dual-homed to enterprise site (PE1 and PE2). SRv6 EVPN VPWS service is run between enterprise sites (PE1, PE2, and CPE). When one PE fails, services can be rapidly switched to the other PE, minimizing the impact on services.

As shown in Figure 1, deploy fast reroute(FRR) service on PE1 and PE2. When the AC(attachment circuit) link on PE1 fails, PE1 receives downlink traffic and can bypass it to the PE2 device for forwarding. PE2 is also the same. If the AC side links on PE1 and PE2 fail together, a brief traffic loop between PE1 and PE2 occurs. The traffic loop will waste the forwarding resources of the equipment and cause performance pressure. The length of the traffic loop depends on the convergence of the control plane. That is, PE1 withdraws the per-EVI Ethernet A-D route advertised to PE2. The FRR backup path on PE2 is destroyed. PE2 does not send traffic to PE1. In order to solve the above problem, this document defines the SRv6 SID Bypass Functions that will be contained in the SRv6 SID Information Sub-TLV [I-D.ietf-bess-srv6-services], and to be advertised with per-EVI Ethernet A-D routes.

                                +-----+
                                | CE2 |
                                +-----+
                                   |
                                +-----+
                                |EVPL1| Local/Remote 
             -------------------| PE3 | Ethernet Tag ID->100/200
                |               +-----+
                |               /      \
                |              /        \
           SRv6 EVPN ELINE    /          \
                |            /            \
                |           /              \
                |      +-----+SRv6 Bypass  +-----+
             --------- | PE1 | Tunnel      | PE2 |
L/R Ethernet           |EVPL1|-------------|EVPL1| L/R Ethernet 
Tag ID->200/100        +-----+             +-----+ Tag ID->200/100
                             \             /
                              \           /
                              ESI1      ESI1
                                \ Trunk /
                                +\-----/+
                                | \   / |
                                +---+---+
                                    |
                                 +-----+
                                 | CE1 |
                                 +-----+

Figure 1: Basic Networking of the SRv6 EVPN VPWS All-Active Scenario

2. SRv6 SID Bypass Functions

2.1. End.DX2L

The "Endpoint with decapsulation and Layer-2 cross-connect to an local outgoing L2 interface (OIF) only" (End.DX2L for short) is a variant of the endpoint behavior. Allocation is expected from IANA for an End.DX2L function codepoint from the "SRv6 Endpoint Behaviors" sub-registry.

One of the applications of the End.DX2L behavior is the L2VPN/EVPN VPWS [RFC7432][RFC8214] use-case.

The End.DX2L SID MUST be the last segment in a SR Policy, and it is associated with one outgoing interface I.

When N receives a packet destined to S and S is a local End.DX2L SID, N does:

S01. When an SRH is processed {
S02.   If (Segments Left != 0) {
S03.      Send an ICMP Parameter Problem to the Source Address,
             Code 0 (Erroneous header field encountered),
             Pointer set to the Segments Left field.
             Interrupt packet processing and discard the packet.
S04.   }
S05.   Proceed to process the next header in the packet
S06. }

When processing the Upper-layer header of a packet matching a FIB entry locally instantiated as an SRv6 End.DX2L SID, the following is done:

S01. If (Upper-Layer Header type != 143) {
S02.    Process as per Section 4.1.1 of [I-D.ietf-spring-srv6-network-programming]
S03. }
S04. Remove the outer IPv6 Header with all its extension headers and forward the Ethernet frame to the OIF I.
S05. If (OIF I is down) {
S06.    Interrupt packet processing and discard the packet.
S07. }

3. Control Plane Processing

As shown in Figure 1:

• 1. PE1 advertises per-EVI Ethernet A-D routes to PE2 and PE3. The route carries the SRv6 Service SID (SID Type=2, End.DX2) sid1 and SRv6 Service Bypass SID sid11 allocated by the EVPL1 service on PE1.
• 2. The PE2 device receives the per-EVI Ethernet A-D route advertised by PE1 and finds that it is the same as the Local/Remote Ethernet Tag ID and ESI1 of its own EVPL1. PE2 considers it to be a dual-homing relationship with PE1. PE2 uses the SRv6 Service Bypass SID to establish an SRv6 bypass path to PE1. The tunnel is marked as sid11. The SRv6 Service Bypass SID takes effect when its EVPL Local/Remote Ethernet Tag ID and ESI are the same as the per-EVI Ethernet A-D route received.
• 3. The EVPL1 Local/Remote Ethernet Tag ID of the PE3 device matches PE1. PE3 uses the SRv6 Service SID to establish an EVPN VPWS service to PE1. The service is marked as sid1. PE3's EVPL1 Local/Remote Ethernet Tag ID and ESI are different from the per-EVI Ethernet A-D routes received. PE3 should ignore this attribute.
• 4. In the same way, PE2 advertises per-EVI Ethernet A-D routes to PE1 and PE3. The routes carry the SRv6 Service SID sid2 and SRv6 Service Bypass SID sid22 allocated by EVPL1 services on PE2.
• 5. Finally, the primary path from PE1 to CE1 is the local AC port and the bypass path is the SRv6 tunnel labeled by sid22. The primary path from PE2 to CE1 is the local AC port and the bypass path is the SRv6 tunnel labeled by sid11. Paths from PE3 to PE1 and PE2 are marked as sid1 and sid2.

4. Data Plane Processing

This section will describe the processes of the downlink Layer 2 packet forwarding cases.

As shown in Figure 1:

• 1. After receiving a Layer 2 packet sent by the CE2, PE3 encapsulates the packet with the EVPL1 sid1 as the destination IPv6 of the SRH header, and forwards the packet to PE1.
• 2. After receiving a Layer 2 packet sent by the PE3, PE1 parses the EVPL1 sid1 of the SRH header and forwards it according to the function End.DX2 of sid1. When the primary path from PE1 to CE1 fails, PE1 encapsulates the packet with the EVPL1 bypass sid22 as the destination IPv6 of the SRH header, and forwards the packet to PE2.
• 3. After receiving a Layer 2 packet sent by the PE1, PE2 parses the EVPL1 bypass sid22 of the SRH header and forwards it according to the function End.DX2L of sid22. When the primary path from PE2 to CE1 fails, PE2 discards the packet and successfully breaks the loop.
• 4. As above, if PE2 receives a Layer 2 packet from PE3, EVPL1 bypass sid11 can also been used to break the loop.

5. IANA Considerations

TBD

6. Security Considerations

TBD

7. Contributors

   Shunwan Zhuang
   Huawei Technologies

   Email: zhuangshunwan@huawei.com

   Chongyang Hu
   Huawei Technologies
   
   Email: huchongyang@huawei.com
   
   Bingshe Liu
   Huawei Technologies

   Email: liubingshe@huawei.com

The following individuals gave significant contributions to this document:

8. Acknowledgements

The authors would like to thank xxx for the discussion and review of this document.

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses