Network Working Group Z. Hu Internet-Draft H. Chen Intended status: Standards Track J. Yao Expires: April 25, 2019 Huawei Technologies October 22, 2018 Segment Routing Proxy Forwarding draft-hu-spring-segment-routing-proxy-forwarding-00 Abstract Segment Routing Traffic Engineering (SR-TE) supports the creation of explicit paths using adjacency-sids, node-sids, and binding-sids. In the SR-TE path, by providing proxy forwarding to the neighbor nodes of the faulty node, it is ensured that the traffic can reach the neighbor node of the faulty node normally in the case of the SR-TE of the loose path or strict path. If the failed node is a node that provides the Binding-sids service, the neighbor node can perform the binding-sids forwarding behavior to swap the corresponding label stack through the proxy forwarding of the neighbor node. [I-D.bashandy-rtgwg-segment-routing-ti-lfa] defines the usecase of protecting the node failure of segment list. This document describes how to implement the proxy forwarding mechanism of a faulty node at the neighbor node of the faulty node on the SR-TE path . 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 [RFC2119]. 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 April 25, 2019. Hu, et al. Expires April 25, 2019 [Page 1] Internet-Draft Segment Routing Proxy Forwarding October 2018 Copyright Notice Copyright (c) 2018 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 2. IGP extended for proxy forwarding . . . . . . . . . . . . . . 3 2.1. ISIS proxy forwarding Prefix-SID . . . . . . . . . . . . 3 2.2. ISIS Path Binding TLV . . . . . . . . . . . . . . . . . . 4 3. Building proxy forwarding table . . . . . . . . . . . . . . . 5 3.1. Advertise proxy forwarding TLV . . . . . . . . . . . . . 7 3.2. Calculate the proxy forwarding table . . . . . . . . . . 7 4. Node Protection for Segment List . . . . . . . . . . . . . . 8 4.1. Next segment is an adjacency segment . . . . . . . . . . 9 4.2. Next segment is a node segment . . . . . . . . . . . . . 11 4.3. Next segment is a binding segment . . . . . . . . . . . . 13 5. Other scenario considerations . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction Segment Routing Traffic Engineering (SR-TE) is a technology that implements traffic engineering using Segment Routing. Segment Routing-Traffic Engineering supports the creation of explicit paths using adjacency-sids, node-sids, and binding-sids. After a node failure causes the network to reconverge, the node in the network deletes the forwarding entry generated for the faulty node locally. In the case of SR-TE loose path, traffic cannot reach to the neighbor node of the faulty node because the forwarding entry is deleted. Any traffic protection policy of the neighbor node cannot take effect. Hu, et al. Expires April 25, 2019 [Page 2] Internet-Draft Segment Routing Proxy Forwarding October 2018 If the faulty node is a label adhesion node, the Binding-sids cannot be exchanged to the label stack for its identity, and the traffic will be lost before it reaches the faulty node. In this document, the proxy mechanism is provided in the neighbor node of the faulty node of the forwarding path to implement traffic forwarding after the node fault on the SR-TE loose path and the label adhesion scenario. 2. IGP extended for proxy forwarding When a node has segment routing proxy forwarding capability, it must advertise the proxy global sid of the neighbor node.Unless this node has an anycast sid same as the neighbor node.It is used to announce that the node has the ability to proxy forward the sid. When the node who advertises this global sid fails, the traffic can be forwarded to the proxy node. 2.1. ISIS proxy forwarding Prefix-SID The ISIS SID/Label Binding TLV (suggested value 149) is defined in [I-D.ietf-isis-segment-routing-extensions] . A proxy node uses the SID/Label Binding TLV to advertise the Prefix-Sid of its neighbor node. The reserved bit of the Flags field of the SID/Label Binding TLV is extended by a P flag, and the Prefix-Sid is identified as a proxy forwarding Prefix-SID. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Flags | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range | Prefix Length | Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Prefix (continued, variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SubTLVs (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |F|M|S|D|A|P| | +-+-+-+-+-+-+-+-+ Where: Hu, et al. Expires April 25, 2019 [Page 3] Internet-Draft Segment Routing Proxy Forwarding October 2018 P-Flag: Proxy forwarding flag. If set, this Prefix-Sid is advertised by the proxy node.This TLV is used to announce that the node has the ability to proxy forward the Prefix-Sid. 2.2. ISIS Path Binding TLV TE-PATH-BINDING TLV is defined in [I-D.sivabalan-pce-binding-label-sid], For supporting Binding sid proxy forwarding. This document introduces TE-PATH-BINDING TLV to the ISIS. [I-D.ietf-spring-segment-routing-policy] has defined the usage of binding-sid. In the ISIS, the format of Path Binding TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Binding Type (BT) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Binding Value (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: Type:TBD, to be assigned by IANA. Length: variable. Binding Type (BT): identify the type of binding included in the TLV. This document specifies the following BT values: o BT = 0: The binding value is an MPLS label carried in the format specified in [RFC5462] where only the label value is valid, and other fields (TC, S, and TTL) MUST be considered invalid. The Length MUST be set to 6. o BT = 1: Similar to the case for BT = 0 except that all the fields on the MPLS label entry are set on transmission. However, the receiver MAY choose to override TC, S, and TTL values according its local policy. Binding Value: A variable length field, padded with trailing zeros to a 4-byte boundary. For the BT = 0, the 20 bits represents the MPLS label. For the BT = 1, the 32-bits represents the label stack entry as per [RFC5462]. Hu, et al. Expires April 25, 2019 [Page 4] Internet-Draft Segment Routing Proxy Forwarding October 2018 3. Building proxy forwarding table Hu, et al. Expires April 25, 2019 [Page 5] Internet-Draft Segment Routing Proxy Forwarding October 2018 Node Sid:2 Node Sid:3 +-----+ +-----+ | |----------+ | / |RT2 | | RT3 |\ / +-----+ +-----+ \ / | \ /| \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ Node Sid:1 | \ / | \Node Sid:4 Node Sid:5 +-----+ | \ / | +-----+ +-----+ | | | X | | |-------| | | RT1 | | / \ | | RT4 | | RT5 | +-----+ | / \ | +-----+ +-----+ \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \| / \ |/ | / \ +-----+ +-----+ / \ | | | |/ \ | RT6 |-----------| RT7 | +-----+ +-----+ Node Sid:6 Node Sid:7 +------------------+ +----------------+ | Node SRGB | | label stack | +------------------+ +----------------+ | RT1:[1000-1999] | | 1003 | +------------------+ +-----------------+ +----------------+ | RT2:[2000-2999] | | Adj-Sid | | 3004 | +------------------+ +-----------------+ +----------------+ | RT3:[3000-3999] | |RT3->RT6:3036 | | 4005 | +------------------+ +-----------------+ +----------------+ | RT4:[4000=4999] | |RT3->RT7:3037 | +------------------+ +-----------------+ | RT5:[5000-5999] | |RT3->RT4:3034 | +------------------+ +-----------------+ | RT6:[6000-6999] | |RT7->RT4:7074 | +------------------+ +-----------------+ | RT7:[7000-7999] | |RT4->RT5:4045 | +------------------+ +-----------------+ Figure 1. Topolocy of SR-TE path Hu, et al. Expires April 25, 2019 [Page 6] Internet-Draft Segment Routing Proxy Forwarding October 2018 We use Figure 1 to illustrate the SR proxy forwarding approach. Each node N has SRGB = [N000-N999], RT1 is an ingress node of SR domain . A label stack that represents the path R1->R3->R4->R5 is shown as well. In the figure,RT3 is a failure node , RT2 is a Point of Local Repair (PLR) node. 3.1. Advertise proxy forwarding TLV If the Point of Local Repair (PLR) has proxy forwarding ability, for example, RT2. When node RT2 learns the prefix-sid of the direct neighbor RT3, it must use the proxy forwarding TLV to advertise the prefix-sid learned from RT3. When RT3 fails, RT2 needs to maintain proxy forwarding TLV for a period of time. When the proxy forwarding table corresponding to the fault node is deleted (see section 3.2), the proxy forwarding TLV is withdrawn. The nodes in the network (for example, RT1) learn the Prefix-Sid TLV advertised by RT3 and the proxy forwarding TLV advertised by RT2, when RT3 is normal, the nodes prefer Prefix-Sid TLV. When the RT3 fails, the proxy forwarding TLV advertised by RT2 is preferred. 3.2. Calculate the proxy forwarding table The SR proxy node needs to calculate a proxy forwarding table for each neighbor, each neighbor has an independent proxy forwarding table. The Node P (PLR) generates a proxy forwarding table for Node N, and P needs to contain the following information: 1: Node N's SRGB range and the difference between the SRGB start value of node P and that of node N; 2: All adjacency-SID of N and Node-SID of the node pointed to by NODE N's adjacency-SID. 3: The binding-SID of N and the label stack associated with binding- SID of N. NODE P (PLR) uses a proxy forwarding table based on the next segment to find a node N as a backup forwarding entry to the adj-SID and Node-SID of the N. When the N fails, the proxy forwarding table needs to be maintained for a period of time, which is recommended for 30 minutes. Node RT3 in the topology of Figure 1 is the node N, and the node RT2 is the P (PLR). RT2 calculates the proxy forwarding table for RT3, as shown in Figure 2. Hu, et al. Expires April 25, 2019 [Page 7] Internet-Draft Segment Routing Proxy Forwarding October 2018 RT2's Routing Table (partial) +==========+====================================+===========+=======+ | In-Label | Action | Out-Label | TYPE | +==========+====================================+===========+=======+ | 2003 | pop, fwd to RT3 | 3003 |Primary| | | pop, lookup Proxy Forwarding table | |Backup | +----------+--------------------------------------------------------+ | 2004 |pop, fwd to RT3 | 3004 |Primary| | |pop, fwd to RT7 | 7004 |Backup | +----------+--------------------------------------------------------+ RT2's Proxy Forwarding Table for RT3 (partial) +==========+===============+============+=============+==============+ | In-label | SRGBDiffValue | Next Label | Action | Map Label | +==========+===============+============+=============+==============+ | 2003 | -1000 | 3034 | Fwd to RT4 | 2004 | +----------+---------------+------------+-------------+--------------+ | 3036 | Fwd to RT6 | 2006 | +------------+-------------+--------------+ | 3037 | Fwd to RT7 | 2007 | +------------+-------------+--------------+ | 100 | Swap to { 3034, 4045 } | +------------+-------------+--------------+ Figure 2. RT2's Routing Table and Proxy Forwarding Table for RT3 (partial) Where: In-Lable: Local Node SRGB starting value + Node-Sid of protected node RT3. SRGBDiffValue: Local node(RT2) SRGB starting value - Protected node(RT3) SRGB starting value. Next Label: Generate forwarding entries for adj-Sids and binding-sids of Protected node(RT3). Map Label: the PLR swaps the Next Label to the Map Label, and then queries the PLR Routing Table again according to the Map Label to obtain the out-label. 4. Node Protection for Segment List Segment Routing Traffic Engineering supports the creation of explicit paths using adjacency-sids, node-sids, and binding-sids. The label stack is a combination of one or more of adjacency-sids, node-sids, and binding-sids. This Section shows how the P-node uses the SR Hu, et al. Expires April 25, 2019 [Page 8] Internet-Draft Segment Routing Proxy Forwarding October 2018 proxy forwarding mechanism to protect traffic to the destination node when the next segment of label stack is adjacency-sids, node-sids, or binding-sids, respectively. 4.1. Next segment is an adjacency segment Hu, et al. Expires April 25, 2019 [Page 9] Internet-Draft Segment Routing Proxy Forwarding October 2018 Node Sid:2 Node Sid:3 +-----+ +-----+ | |----------+ | / |RT2 | | RT3 |\ / +-----+ +-----+ \ / | \ /| \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ Node Sid:1 | \ / | \Node Sid:4 Node Sid:5 +-----+ | \ / | +-----+ +-----+ | | | X | | |-------| | | RT1 | | / \ | | RT4 | | RT5 | +-----+ | / \ | +-----+ +-----+ \ | / \ | / \ | / \ | /2 \ | / \ | /ru \ | / \ | / \ | / \| / \ |/ | / \ +-----+ +-----+ / \ | | | |/ \ | RT6 |-----------| RT7 | +-----+ +-----+ Node Sid:6 Node Sid:7 +------------------+ +-----------------+ +----------------+ | Node SRGB | | Adj-Sid | | Label Stack | +------------------+ +-----------------+ +----------------+ | RT1:[1000-1999] | |RT1->RT2:1012 | | 1012 | +------------------+ +-----------------+ +----------------+ | RT2:[2000-2999] | |RT2->RT3:2023 | | 2023 | +------------------+ +-----------------+ +----------------+ | RT3:[3000-3999] | |RT3->RT6:3036 | | 3034 | +------------------+ +-----------------+ +----------------+ | RT4:[4000=4999] | |RT3->RT7:3037 | | 4045 | +------------------+ +-----------------+ +----------------+ | RT5:[5000-5999] | |RT3->RT4:3034 | +------------------+ +-----------------+ | RT6:[6000-6999] | |RT7->RT4:7074 | +------------------+ +-----------------+ | RT7:[7000-7999] | |RT4->RT5:4045 | +------------------+ +-----------------+ Figure 3. Next Segment is adj-SID for Node Protection Hu, et al. Expires April 25, 2019 [Page 10] Internet-Draft Segment Routing Proxy Forwarding October 2018 As shown in Figure 3, the SR-TE strict explicit path is RT1->RT2->RT3->RT4->RT5, identified by the label stack { 1012, 2023, 3034, 4045 }. The adj-sid: 3034, which is used to identify the traffic forwarding path of the RT3->RT4. Node RT2 acts as a PLR node, and uses next adj-SID of the label stack to lookup the proxy forwarding table calculated by RT2 locally for RT3. The queried path is the label forwarding path of the next hop node of RT3, which bypasses RT3. The specific steps are as follows: a. RT1 pops top adj-SID 1012, and forwards packets to RT2; b. RT2 identifies the next hop node RT3 fault, pops top adj-SID 2023, and queries Proxy Forwarding Table with the next sid (3034). The query result is forwarding packets to RT4, the map label is 2004; c. RT2 swaps the label 3034 to map label 2004, and then uses the map label 2004 to query RT2's Routing Table. Due to RT3 failure, the result of the query is forwarding the packets to RT7 (backup path) , and the out-label is 7004. d. RT2 swaps the label 2004 to out-label 7004, and forwards packets to RT7. RT7 queries the local routing table to forward to RT4. 4.2. Next segment is a node segment Hu, et al. Expires April 25, 2019 [Page 11] Internet-Draft Segment Routing Proxy Forwarding October 2018 Node Sid:2 Node Sid:3 +-----+ +-----+ | |----------+ | / |RT2 | | RT3 |\ / +-----+ +-----+ \ / | \ /| \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ Node Sid:1 | \ / | \Node Sid:4 Node Sid:5 +-----+ | \ / | +-----+ +-----+ | | | X | | |-------| | | RT1 | | / \ | | RT4 | | RT5 | +-----+ | / \ | +-----+ +-----+ \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \| / \ |/ | / \ +-----+ +-----+ / \ | | | |/ \ | RT6 |-----------| RT7 | +-----+ +-----+ Node Sid:6 Node Sid:7 +------------------+ +-----------------+ +----------------+ | Node SRGB | | Adj-Sid | | Label Stack | +------------------+ +-----------------+ +----------------+ | RT1:[1000-1999] | |RT1->RT2:1012 | | 1003 | +------------------+ +-----------------+ +----------------+ | RT2:[2000-2999] | |RT2->RT3:2023 | | 3004 | +------------------+ +-----------------+ +----------------+ | RT3:[3000-3999] | |RT3->RT6:3036 | | 4005 | +------------------+ +-----------------+ +----------------+ | RT4:[4000=4999] | |RT3->RT7:3037 | +------------------+ +-----------------+ | RT5:[5000-5999] | |RT3->RT4:3034 | +------------------+ +-----------------+ | RT6:[6000-6999] | |RT7->RT4:7074 | +------------------+ +-----------------+ | RT7:[7000-7999] | |RT4->RT5:4045 | +------------------+ +-----------------+ Figure 4. Next Segment is node-SID for Node Protection Hu, et al. Expires April 25, 2019 [Page 12] Internet-Draft Segment Routing Proxy Forwarding October 2018 As shown in Figure 4, the SR-TE loose path is RT1->RT3->RT4->RT5, which is identified by the label stack {1003, 3004, 4005}. When the node RT3 fails, the proxy forwarding TLV advertised by the RT2 is preferred to direct the traffic of the RT1 to the PLR node RT2. Node RT2 acts as a PLR node and queries the proxy forwarding table locally calculated for RT3. The queried path is the label forwarding path of the next hop node of RT3, which bypasses RT3. The specific steps are as follows: a. RT1 swaps label 1003 to out-label 2003 to RT3. b. RT2 receives the label forwarding packet whose top label of label stack is 2003, and searches for the local Routing Table, the behavior found is lookup Proxy Forwarding table due to RT3 failure. c. RT2 uses 2003 as the in-label to lookup Proxy Forwarding tabel, and finds that the SRGB difference between local node and the faulty node is -1000. The next label(3004) of the label stack (top label 2003 pop) and the SRGB difference are used to recalculated the new in-label[ 3004+（-1000）= 2004 ]. d. Uses the new in-label(2004) to lookup the RT2's Routing Table. because of RT3 failure, the backup path is searched directly, and the behavior of backup path is forwarded to RT7, out-label is 7004. e. RT2 swaps the label 2004 to out-label 7004, and forwards packets to RT7. RT7 queries the local routing table to forward to RT4. 4.3. Next segment is a binding segment Hu, et al. Expires April 25, 2019 [Page 13] Internet-Draft Segment Routing Proxy Forwarding October 2018 Node Sid:2 Node Sid:3 +-----+ +-----+ | |----------+ | / |RT2 | | RT3 |\ / +-----+ +-----+ \ / | \ /| \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ / | \ Node Sid:1 | \ / | \Node Sid:4 Node Sid:5 +-----+ | \ / | +-----+ +-----+ | | | X | | |-------| | | RT1 | | / \ | | RT4 | | RT5 | +-----+ | / \ | +-----+ +-----+ \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \| / \ |/ | / \ +-----+ +-----+ / \ | | | |/ \ | RT6 |-----------| RT7 | +-----+ +-----+ Node Sid:6 Node Sid:7 +------------------+ +-----------------+ +----------------+ | Node SRGB | | Adj-Sid | | Label Stack | +------------------+ +-----------------+ +----------------+ | RT1:[1000-1999] | |RT1->RT2:1012 | | 1003 | +------------------+ +-----------------+ +----------------+ | RT2:[2000-2999] | |RT2->RT3:2023 | | 100 | +------------------+ +-----------------+ +----------------+ | RT3:[3000-3999] | |RT3->RT6:3036 | +------------------+ +-----------------+ | RT4:[4000=4999] | |RT3->RT7:3037 | +------------------+ +-----------------+ | RT5:[5000-5999] | |RT3->RT4:3034 | +------------------+ +-----------------+ | RT6:[6000-6999] | |RT7->RT4:7074 | +------------------+ +-----------------+ | RT7:[7000-7999] | |RT4->RT5:4045 | +------------------+ +-----------------+ Figure 5. Next Segment is Binding-SID for Node Protection Hu, et al. Expires April 25, 2019 [Page 14] Internet-Draft Segment Routing Proxy Forwarding October 2018 As shown in Figure 4, the SR-TE loose path is RT1->RT3->RT4->RT5, which is identified by the label stack { 1003,100 },where 100 is a Binding-Sid, which represents the label combination of { 3034, 4045}. When the node RT3 fails, the proxy forwarding TLV advertised by the RT2 is preferred to direct the traffic of the RT1 to the PLR node RT2. Node RT2 acts as a PLR node and uses Binding-SID to query the proxy forwarding table locally calculated for RT3. The queried path is the label forwarding path of the next hop node of RT3, which bypasses RT3. The specific steps are as follows: a. RT1 swaps label 1003 to out-label 2003 to RT3. b. RT2 receives the label forwarding packet whose top label of label stack is 2003, and searches for the local Routing Table, the behavior found is lookup Proxy Forwarding table due to RT3 failure. c. RT2 uses Binding-sid:100(label 2003 has pop) as the in-label to lookup the Next Label record of the Proxy Forwarding Tabel, the behavior found is swap to Segment list { 3034, 4045 }. d. RT2 swaps Binding-sid:100 to Segment list { 3034, 4045 }, and RT2 Uses the 3034 to lookup the Next Label record of the Proxy Forwarding table again. The behavior found is Forward to RT4, and the map label is 2004. e. Uses the new in-label(2004) to lookup the RT2's Routing Table. because of RT3 failure, the backup path is searched directly, and the behavior of backup path is forwarded to RT7, out-label is 7004. f. RT2 swaps the label 2004 to out-label 7004, and forwards packets to RT7. RT7 queries the local routing table to forward to RT4. 5. Other scenario considerations The implementation for SRv6 and egress protection will be added in subsequent documentation. 6. IANA Considerations TBD 7. Security Considerations TBD Hu, et al. Expires April 25, 2019 [Page 15] Internet-Draft Segment Routing Proxy Forwarding October 2018 8. Acknowledgements TBD 9. References 9.1. 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, . 9.2. Informative References [I-D.bashandy-rtgwg-segment-routing-ti-lfa] Bashandy, A., Filsfils, C., Decraene, B., Litkowski, S., Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P. Camarillo, "Topology Independent Fast Reroute using Segment Routing", draft-bashandy-rtgwg-segment-routing-ti- lfa-05 (work in progress), October 2018. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS Extensions for Segment Routing", draft-ietf-isis- segment-routing-extensions-19 (work in progress), July 2018. [I-D.ietf-spring-segment-routing-policy] Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d., bogdanov@google.com, b., and P. Mattes, "Segment Routing Policy Architecture", draft-ietf-spring-segment-routing- policy-01 (work in progress), June 2018. [I-D.sivabalan-pce-binding-label-sid] Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J., Previdi, S., and D. Dhody, "Carrying Binding Label/ Segment-ID in PCE-based Networks.", draft-sivabalan-pce- binding-label-sid-05 (work in progress), October 2018. [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, . Hu, et al. Expires April 25, 2019 [Page 16] Internet-Draft Segment Routing Proxy Forwarding October 2018 Authors' Addresses Zhibo Hu Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: huzhibo@huawei.com Huaimo Chen Huawei Technologies Boston, MA USA Email: Huaimo.chen@huawei.com Junda Yao Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: yaojunda@huawei.com Hu, et al. Expires April 25, 2019 [Page 17]