LSR Working Group U. Chunduri, Ed. Internet-Draft Huawei USA Intended status: Standards Track J. Tantsura Expires: September 6, 2018 Nuage Networks Y. Qu Huawei Technologies March 5, 2018 Usage of Non Shortest Path Forwarding (NSPF) Ids in IS-IS draft-ct-isis-nspfid-for-sr-paths-00 Abstract This document specifies the advertisement of Non Shortest Path Forwarding IDentifier (NSPF ID) TLV and the computation procedures for the same in IS-IS protocol. NSPF ID allows to simplify the data plane path description of data traffic in SR deployments. This helps mitigate the MTU issues that are caused by additional SR overhead of the packet and allows traffic statistics. 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 RFC2119 [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 September 6, 2018. Chunduri, et al. Expires September 6, 2018 [Page 1] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 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 1.1. Mitigation with MSD and RLD . . . . . . . . . . . . . . . 3 1.2. Issues with Increased SID Depth . . . . . . . . . . . . . 3 1.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Non Shortest Path Forwarding IDentifier TLV . . . . . . . . . 5 2.1. Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2. NSPF-ID Fields . . . . . . . . . . . . . . . . . . . . . 7 2.3. NSP sub-TLVs . . . . . . . . . . . . . . . . . . . . . . 8 2.4. Non-NSP sub-TLVs . . . . . . . . . . . . . . . . . . . . 9 3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 9 4. NSPF ID Data plane aspects . . . . . . . . . . . . . . . . . 11 5. NSP Traffic Accounting . . . . . . . . . . . . . . . . . . . 11 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 9.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 1. Introduction In a network implementing source routing, packets may be transported through the use of segment identifiers (SIDs), where a SID uniquely identifies a segment as defined in [I-D.ietf-spring-segment-routing]. In SR-MPLS, a segment is encoded as a label and an ordered list of segments is encoded as a stack of labels. In SRv6, a segment is encoded as an IPv6 address, with a new type of IPv6 routing header called SRH. An ordered list of segments is encoded as an ordered list of IPv6 addresses in SRH [I-D.ietf-6man-segment-routing-header]. Chunduri, et al. Expires September 6, 2018 [Page 2] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 The segment may include one or more nodes, unidirectional adjecencies between two nodes or service instruction by a particular node in the network. A Non Shortest Path (NSP) may be described using list of segments in SR. However, this creates a problem of having a relatively large stack imposed on the data packet. A path that is encoded with SIDs can be a loose or strict path. In a strict path all the nodes/links on the path are encoded as SIDs, with the expense of number of total SIDs in the stack. 1.1. Mitigation with MSD and RLD The number of SIDs in the stack a node can impose is referred as Maximum SID Depth (MSD) capability [I-D.ietf-isis-segment-routing-msd], which must be taken into consideration when computing a path to transport a data packet in a network implementing segment routing. [I-D.ietf-isis-mpls-elc] defines Readable Label Depth (RLD) that is used by a head-end to insert Entropy Label pair (ELI/EL) at appropriate depth, so it could be read by transit nodes. There are situations where the source routed path can be excessive as path represented by SR SIDs need to describe all the nodes and ELI/EL based on the readability of the nodes in that path. While MSD (and RLD) capabilities advertisement help mitigate the problem for a central entity to create the right source routed path per application/operator requirements; actual depth is still limited by the underlying hardware in the data path. 1.2. Issues with Increased SID Depth Consider the following network where SR-MPLS data plane is in use and with same SRGB (5000-6000) on all nodes i.e., A1 to A7 and B1 to B7 for illustration: SID:10 SID:20 SID:30 SID:40 SID:50 SID:300(Ax) SID:60 SID:70 A1-------A2-------A3-------A4-------A5===============A6----------A7 \ / \ SID:310(Ay) \ / \ 10 10/ \ \10 /10 \ / \ \ / SID:80 \A8-----A9/SID:90 \ 40 \ / / \ +-----+ \ / /10 \10 \ \/ B1--------B2-----------B3----B4--------B5-------B6----------B7 SID:110 SID:120 SID:130 SID:140 SID:150 SID:160 SID:170 Figure 1: SR-MPLS Network Chunduri, et al. Expires September 6, 2018 [Page 3] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 Global ADJ SIDs are provisioned between A5 and A6 .All other SIDs shown are nodal SID indices. All metrics of the links are set to 1, other values as configured. Shortest Path from A1 to A7: A2-A3-A4-A5-A6-A7 Shortest Path from B1 to B7: B2-B3-B4-B5-B6-B7 SR-PATH-1: From A1 to A7 - A2-A8-B2-B3-A9-A5-Ax-A7; Pushed Label Stack @A1: 5070:5300:5050:5090:5130:5120:5080:5020 SR-PATH-2: From B1 to B7 - B2-A8-A2-A4-A9-B4-B6-B7; Pushed Label Stack @B1: 5170:5160:5140:5090:5040:5020:5080:5120 In the above example both SR-PATH-1 and SR-PATH-2 are represented with a combination of Adjacency and Node SIDs with a stack of 8 labels each. However, this value can be larger, if the use of entropy label is desired and based on the RLD capabilities of each node and additional labels required to insert ELI/EL at appropriate places. Though above network is shown with SR-MPLS data plane, problem is similar if the network were a SR-IPv6 network with all SIDs encoded as IPv6 SIDs in SRH. In various SR deployments, the following issues may arise: Not all nodes in the path can support MSD or RLD needed to satisfy user/operator requirements, when the number of SIDs increased to describe the source routed path. This problem gets multiplied by four times in SRH compared to MPLS data plane because of the SID size (16 bytes) in SRH. Even if all nodes can support the required MSD or RLD, the bigger label stack/depth can cause potential MTU/fragmentation issues. In some deployments, it is also required reducing the overhead in the network layer, especially for low packet size packets, where the actual data can be way lesser than all encapsulations and SR path overheads. Apart from the above some deployments need path accounting statistics for path monitoring and traffic re-optimizations. [I-D.hegde-spring-traffic-accounting-for-sr-paths] proposes a solution, however this further increases the depth of SID stack. The approach could be counter productive in the environments, where SID depth is already causing deployment issues as listed above. Chunduri, et al. Expires September 6, 2018 [Page 4] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 To mitigate the above issues, and also to facilitate forwarding plane a mechanism to identify the SR path with a corresponding data plane identifier for accounting of traffic for SR paths, this draft proposes a new IS-IS TLV (Section 2) to advertise the NSPs with Non Shortest Path Forwarding IDentifier (NSPF ID). This draft lays out procedure for IS-IS nodes to how to use NSPF ID TLV in Section 3. With corresponding data plane, Section 3 mechanism, reduces the SID stack in the data plane from 8 SIDs shown in SR-PATH-1 and SR-PATH-2 with a single NSPF ID. This draft also introduce source routed paths with NSPF ID types defined for native IPv4 and IPv6 data planes as defined in Section 2.2. 1.3. Acronyms EL - Entropy Label ELI - Entropy Label Indicator MPLS - Multi Protocol Label Switching MSD - Maximum SID Depth MTU - Maximum Transferrable Unit SID - Segment Identifier SPF - Shortest Path First SR - Segment Routing SRH - Segment Routing Header SR-MPLS - Segment Routing with MPLS data plane SRv6 - Segment Routing with Ipv6 data plane with SRH SRH - IPv6 Segment Routing Header TE - Traffic Engineering 2. Non Shortest Path Forwarding IDentifier TLV The NSPF-ID TLV has Type TBD (suggested value xxx), and has the following format: Chunduri, et al. Expires September 6, 2018 [Page 5] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 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 | Reserved | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | Prefix Len | FEC Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // FEC Prefix (continued, variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NSPF-ID Type | NSPF-ID Len | NSPF-ID Flags | NSPF-ID Algo | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // NSPF-ID (continued, variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |No.of NSP-STs | NSP sub-TLVs (Variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |No.of Other-STs| Non-NSP sub-TLVs(variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: NSPF ID TLV Format Type - TBD from IS-IS top level TLV registry. Length - Total length of the value field in bytes (variable). Reserved - 1 Octet reserved bits for future use. Reserved bits MUST be reset on transmission and ignored on receive. Flags - Flags for this TLV are described in Section 2. MT-ID - is the multi-topology identifier defined in [RFC5120] with 4 most significant bits reset on transmission and ignored on receive. The remaining 12-bit field contains the MT-ID. Prefix Len - contains the length of the prefix in bits. Only the most significant octets of the Prefix are encoded. (i.e., 1 octet for prefix length 1 up to 8, 2 octets for prefix length 9 to 16, 3 octets for prefix length 17 up to 24 and 4 octets for prefix length 25 up to 32, ...., 16 octets for prefix length 113 up to 128). FEC Prefix - represents the Forwarding Equivalence Class at the tail-end of the advertised NSP. The 'FEC Prefix' corresponds to a routable prefix of the originating node, meaning one of the [RFC7794] flags MUST be set (X-Flag/R-Flag/N-Flag). Value of this field can be 4 or 16 octets and encoding is similar to TLV 135 and TLV 236 or MT-Capable [RFC5120] IPv4 (TLV 235) and IPv6 Prefixes (TLV 237) respectively. Chunduri, et al. Expires September 6, 2018 [Page 6] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 2.1. Flags Flags: 1 octet field of NSPD ID TLV has following flags defined. These flags mostly related to applicability of this TLV in an L1 area or entire IS-IS domain: NSPF ID Flags Format 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |S|D|A| Rsrvd | +-+-+-+-+-+-+-+-+ S - If set, the NSPF ID TLV SHOULD be flooded across the entire routing domain. If the S flag is not set, the NSPF ID TLV MUST NOT be leaked between IS-IS levels. This bit MUST NOT be altered during the TLV leaking D - when the NSPF ID TLV is leaked from IS-IS level-2 to level-1, the D bit MUST be set. Otherwise, this bit MUST be clear. NSPF ID TLVs with the D bit set MUST NOT be leaked from level-1 to level-2. This is to prevent TLV looping across levels. A - The originator of the NSPF ID TLV MAY set the A bit in order to signal that the prefixes and NSPF-IDs advertised in the NSPF ID TLV are directly connected to their originators. The mechanisms through which the originator of the NSPF ID TLV can figure out if a prefix is attached or not are outside the scope of this document (e.g.: through explicit configuration). If the NSPF ID TLV is leaked to other areas/levels the A-flag MUST be cleared. Rsrvd - reserved bits for future use. Reserved bits MUST be reset on transmission and ignored on receive. Flags defined above are similar to [I-D.ietf-isis-segment-routing-extensions] and section 2.4.1 restrictions apply here. 2.2. NSPF-ID Fields This represents the actual data plane identifier in the packet and could be of any data plane as defined in type field. As with "FEC Prefix", NSPF-ID also need not be from the advertising node of NSPF ID itself. However, both MUST belong to a same node in the network. NSPF-ID Type: This is a new registry (TBD IANA) for this TLV and the defined types are as follows. Type: 1 - MPLS SID/Label Type: Chunduri, et al. Expires September 6, 2018 [Page 7] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 2 Native IPv4 Address Type: 3 Native IPv6 Address Type 4: IPv6 SID in SRv6 with SRH NSPF-ID Len: Length of the NSPF Identifier field in octets and this depends on the NSPF-ID type. NSPF-ID Flags: 1 Octet field for NSPF-ID flags. Some of the bits could be NSPF-ID type specific and each new type MUST define the flags applicable to the NSPF-ID type. For NSPF-ID Type 1, the flags are same as Section 2.1 definition in [I-D.ietf-isis-segment-routing-extensions]. For NSPF-ID Type 2, 3 and NSPF-ID Type 4 only 'R' flag is applicable. Undefined flags for each NSPF-ID type MUST be considered as RESERVED. RESERVED flag bits in each NSPF-ID type specific flags MUST be reset on transmission and ignored on receive. NSPF-ID Algo: 1 octet value represents the SPF algorithm 2.3. NSP sub-TLVs A new sub-TLV registry is created (TBD IANA) called NSP sub-TLVs. These are used to describe the path in the form of set of contiguous sub-TLVs. Total number of the non-NSP sub-TLVs are defined in 1-octet field "No.of NSP-STs" just before the NSP sub-TLVs. Type 1: SID/Lable sub-TLV as defined in Section 2.3 of [I-D.ietf-isis-segment-routing-extensions]. Only Type is defined and Length/Value fields are per Section 2.3 of the referenced document. Type 2: Prefix SID sub-TLV as defined in Section 2.1 of[I-D.ietf-isis-segment-routing-extensions]. Only Type is defined and Length/Value fields are per Section 2.1 of the referenced document. Type 3: Adjacency SID sub-TLV as defined in Section 2.2 of [I-D.ietf-isis-segment-routing-extensions]. Only Type is defined and Length/Value fields are per Section 2.2 of the referenced document. Type 4: Length 4 bytes, value is 4 bytes IPv4 address encoded similar to IPv4 FEC Prefix described above. Type 5: Length 16 bytes, value is 16 bytes IPv6 address encoded similar to IPv4 FEC Prefix described above. Chunduri, et al. Expires September 6, 2018 [Page 8] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 2.4. Non-NSP sub-TLVs NSPF ID TLV also defines a new sub-TLV registry (TBD IANA) for defining extensible set of sub-TLVs other than describing the path sub-TLVs. Total number of the path sub-TLVs to describe the path are defined in 1-octet field "No.of Other-STs" just before the Non-NSP sub-TLVs. This field serves as a demarcation for set of NSP sub-TLVs and Non-NSP sub-TLVs. Type 1: Length 0 No value field. Specifies a counter to count number of packets forwarded on this NSPF-ID. Type 2: Length 0 No value field. Specifies a counter to count number of bytes forwarded on this NSPF-ID specified in the network header (e.g. IPv4, IPv6). Type 3: Length 4 bytes, and Value is metric of this path represented through the NSPF-ID. Different nodes can advertise the same NSPF-ID for the same FEC-Prefix with a different set of NSP sub-TLVs and the receiving node MUST consider the lowest metric value (TBD more, what happens when metric is same for two different set of NSP sub-TLVs). 3. Elements of Procedure Consider the following IS-IS network to describe the operation of NSPF ID TLV as defined in Section 2: Chunduri, et al. Expires September 6, 2018 [Page 9] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 1 _______ / 1 \ +---R2-------R3---+ / \_______/ \ / 1 \ 1 / 2 \ 1 / ______ \ / / \ \ R1------R6 R7-----------R4 \ 2 \______/ 2 / \ 2 / 3 \ / 3 \ 3 / +----R8------R9-----R10--+ 3 \ / 1 \ / 1 +-R11-+ Figure 3: IS-IS Network In the above diagram (Figure 3) node R1 is an ingress node, or a head-end node, and the node R4 may be an egress node or another head- end node. The numbers shown on each of the links between nodes R1-R11 indicate a IS-IS metric as provisioned by the operator. R1 may be configured to receive TE source routed path information from a central entity that comprise NSP information which relates to sources that are attached to R1. The NSP information includes the stack or list of nodes in the NSPs from the source to a destination in the network and the NSPF ID. For example, the NSP information may include a sequential ordering of NSP Sub-TLVS as defined by NSPF-ID type, which specifies the actual path toward a FEC/Prefix by R4. The shortest path may be defined by the following sequence of nodes: R1-R2-R3-R4 based on the configured metrics. The central entity MAY define a few NSPs from R1 to R4 that deviate from the shortest path based on other network characteristic requirements as requested by an application or service. For example, the network characteristics or performance requirements may include bandwidth, jitter, latency, throughput, error rate, etc. A first NSP may be identified by NSPF ID = 2 and may include the path of R1-R6-R7-R4 for a FEC Prefix advertised by R4. A second NSP may be identified by NSPF ID = 3 and may include the path of R1-R8-R9-R10-R4. Each receiving node, determine whether an advertised NSP includes information regarding the receiving node. This MAY be done, during the end of the SPF computation for MTID that is advertised in this Chunduri, et al. Expires September 6, 2018 [Page 10] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 TLV and for the FEC/Prefix. For example, suppose node R9 receives the NSP information, node R9 may ignore the first NSP identified by NSPF ID = 2 because this NSP does not include node R9. However, node R9 may determine that the second NSP identified by NSPF ID = 3 does include the node R9 for the FEC prefix advertised by R4. Therefore, node R9 updates the local forwarding database to include an entry for the destination address of R4 that indicates that when a data packet comprising a NSPF ID of 3 is received, node R9 is now configured to forward the data packet to node R10 instead of R11. This is even though the link to node R10 is associated with a higher cost of 3 than the link to node R11, which is associated with a cost of 1. 4. NSPF ID Data plane aspects Data plane NSPF ID is selected by the entity (e.g., a controller) which selects a particular NSP in the network. Section 2.2 defines various data plane identifier types and a corresponding data plane identifier type and identifier is selected by the entity which selects the NSP. For example if NSPF-ID Type is 1, the NSP belongs to SR-MPLS data plane and the complete NSP stack is represented with a unique SR SID/Label. And same logic applies to other NSPF-ID types. 5. NSP Traffic Accounting As described in Section 2.4, each node described in the NSP sub-TLVs SHOULD provision the hardware to account the traffic statistics as indicated in the non-NSP sub-TLVs for the actual data traffic. When NSP is withdrawn from the originating node, rest of the nodes in the NSP MUST remove the state in respective nodes. This approach, thus is more safe and secure than any mechanism that involves creating state in the nodes with data traffic itself. This is because creation and deletion of the traffic accounting state for NSPs happen through IS-IS LSP processing and IS-IS security Section 8 options are applicable to this TLV. 6. Acknowledgements Thanks to Richard Li, Alex Clemm, Kiran Makhijani and Lin Han for initial discussions on this topic. Earlier versions of draft-ietf-isis-segment-routing-extensions have a mechanism to advertise EROs through Binding SID. Chunduri, et al. Expires September 6, 2018 [Page 11] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 7. IANA Considerations This document requests the following new TLVin IANA IS-IS TLV code- point registry. TLV # Name ----- -------------- TBD NSPF ID TLV This document also requests IANA to create new registries for NSPF ID TLV Flags field, NSPF-ID Type, NSPF-ID Flags, NSP sub-TLVs and Non- NSP sub-TLVs in NSPF ID TLV as described in Section 2. 8. Security Considerations Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310]. Further security analysis for IS-IS protocol is done in [RFC7645]. Advertisement of the additional information defined in this document introduces no new security concerns. 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.hegde-spring-traffic-accounting-for-sr-paths] Hegde, S., "Traffic Accounting for MPLS Segment Routing Paths", draft-hegde-spring-traffic-accounting-for-sr- paths-01 (work in progress), October 2017. [I-D.ietf-6man-segment-routing-header] Previdi, S., Filsfils, C., Raza, K., Dukes, D., Leddy, J., Field, B., daniel.voyer@bell.ca, d., daniel.bernier@bell.ca, d., Matsushima, S., Leung, I., Linkova, J., Aries, E., Kosugi, T., Vyncke, E., Lebrun, D., Steinberg, D., and R. Raszuk, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing-header-08 (work in progress), January 2018. Chunduri, et al. Expires September 6, 2018 [Page 12] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 [I-D.ietf-isis-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Readable Label-stack Depth Using IS-IS", draft-ietf-isis- mpls-elc-03 (work in progress), January 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-15 (work in progress), December 2017. [I-D.ietf-isis-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling MSD (Maximum SID Depth) using IS-IS", draft- ietf-isis-segment-routing-msd-09 (work in progress), January 2018. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-15 (work in progress), January 2018. [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, . [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008, . [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, . [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, . [RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and Authentication for Routing Protocol (KARP) IS-IS Security Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015, . Chunduri, et al. Expires September 6, 2018 [Page 13] Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids March 2018 [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, March 2016, . Authors' Addresses Uma Chunduri (editor) Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: uma.chunduri@huawei.com Jeff Tantsura Nuage Networks 755 Ravendale Drive Mountain View, CA 94043 USA Email: jefftant.ietf@gmail.com Yingzhen Qu Huawei Technologies 2330 Central Expressway Santa Clara, CA 95050 USA Email: yingzhen.qu@huawei.com Chunduri, et al. Expires September 6, 2018 [Page 14]