IS-IS Extensions to Support Segment Routing over the IPv6 Data Plane Cisco Systems
Pribinova Street 10 Bratislava 81109 Slovakia ppsenak@cisco.com
Cisco Systems
Brussels Belgium cfilsfil@cisco.com
Cisco Systems
Milpitas United States of America bashandy@cisco.com
Orange
Chatillon France bruno.decraene@orange.com
Huawei Technologies
huzhibo@huawei.com
Routing Area Networking Working Group The Segment Routing (SR) architecture allows a flexible definition of the end-to-end path by encoding it as a sequence of topological elements called "segments". It can be implemented over the MPLS or the IPv6 data plane. This document describes the IS-IS extensions required to support SR over the IPv6 data plane. This document updates RFC 7370 by modifying an existing registry.
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 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .
Copyright Notice Copyright (c) 2023 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 () 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.
Table of Contents
  • .  Introduction
    • .  Requirements Language
  • .  SRv6 Capabilities Sub-TLV
  • .  Advertising Supported Algorithms
  • .  Advertising Maximum SRv6 SID Depths
    • .  Maximum Segments Left MSD Type
    • .  Maximum End Pop MSD Type
    • .  Maximum H.Encaps MSD Type
    • .  Maximum End D MSD Type
  • .  SRv6 SIDs and Reachability
  • .  Advertising Anycast Property
  • .  Advertising Locators and End SIDs
    • .  SRv6 Locator TLV Format
    • .  SRv6 End SID Sub-TLV
  • .  Advertising SRv6 Adjacency SIDs
    • .  SRv6 End.X SID Sub-TLV
    • .  SRv6 LAN End.X SID Sub-TLV
  • .  SRv6 SID Structure Sub-Sub-TLV
  • . Advertising Endpoint Behaviors
  • . IANA Considerations
    • .  SRv6 Locator TLV
      • .  SRv6 End SID Sub-TLV
      • .  IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability Registry
    • .  SRv6 Capabilities Sub-TLV
    • .  IS-IS Sub-Sub-TLVs for the SRv6 Capabilities Sub-TLV Registry
    • .  SRv6 End.X SID and SRv6 LAN End.X SID Sub-TLVs
    • .  MSD Types
    • .  IS-IS Sub-Sub-TLVs for SRv6 SID Sub-TLVs Registry
    • .  Prefix Attribute Flags Sub-TLV
    • .  IS-IS SRv6 Capabilities Sub-TLV Flags Registry
    • .  IS-IS SRv6 Locator TLV Flags Registry
    • . IS-IS SRv6 End SID Sub-TLV Flags Registry
    • . IS-IS SRv6 Adjacency SID Sub-TLVs Flags Registry
  • . Security Considerations
  • . References
    • .  Normative References
    • .  Informative References
  • Acknowledgements
  • Contributors
  • Authors' Addresses
Introduction With Segment Routing (SR) , a node steers a packet through an ordered list of instructions, which are called segments. Segments are identified through Segment Identifiers (SIDs). SR can be directly instantiated on the IPv6 data plane through the use of the Segment Routing Header (SRH) defined in . SRv6 refers to this SR instantiation on the IPv6 data plane. The network programming paradigm is central to SRv6. It describes how any behavior can be bound to a SID and how any network program can be expressed as a combination of SIDs. This document specifies IS-IS extensions that allow the IS-IS protocol to encode some of these SIDs and their behaviors. Familiarity with the network programming paradigm is necessary to understand the extensions specified in this document. The new SRv6 Locator top-level TLV announces SRv6 Locators -- a form of summary address for the set of topology-/algorithm-specific SIDs instantiated at the node. The SRv6 Capabilities sub-TLV announces the ability to support SRv6. Several new sub-TLVs are defined to advertise various SRv6 Maximum SID Depths (MSDs). The SRv6 End SID sub-TLV, the SRv6 End.X SID sub-TLV, and the SRv6 LAN End.X SID sub-TLV are used to advertise which SIDs are instantiated at a node and what Endpoint behavior is bound to each instantiated SID. This document updates by modifying an existing registry ().
Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.
SRv6 Capabilities Sub-TLV A node indicates that it supports the SR Segment Endpoint Node functionality as specified in by advertising a new SRv6 Capabilities sub-TLV of the Router Capability TLV . The SRv6 Capabilities sub-TLV may contain optional sub-sub-TLVs. No sub-sub-TLVs are currently defined. The SRv6 Capabilities sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | optional sub-sub-TLVs...
Type:
25. Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is 2 + length of sub-sub-TLVs.
Flags:
2 octets. The following flags are defined: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |O| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
O-flag:
If set, the router supports use of the O-bit in the SRH, as defined in . The remaining bits, including bit 0, are reserved for future use. They MUST be set to zero on transmission and MUST be ignored on receipt.
Advertising Supported Algorithms An SRv6-capable router indicates one or more supported algorithms by advertising the Segment Routing Algorithm sub-TLV, as defined in .
Advertising Maximum SRv6 SID Depths defines the means to advertise node-/link-specific values for MSDs of various types. Node MSDs are advertised in a sub-TLV of the Router Capability TLV . Link MSDs are advertised in a sub-TLV of TLVs 22, 23, 25, 141, 222, and 223. This document defines the relevant SRv6 MSDs and requests MSD type assignments in the "IGP MSD-Types" registry created by .
Maximum Segments Left MSD Type The Maximum Segments Left MSD Type signals the maximum value of the "Segments Left" field in the SRH of a received packet before applying the Endpoint behavior associated with a SID. SRH Max Segments Left Type: 41 If no value is advertised, the supported value is 0.
Maximum End Pop MSD Type The Maximum End Pop MSD Type signals the maximum number of SIDs in the SRH to which the router can apply "Penultimate Segment Pop (PSP) of the SRH" or "Ultimate Segment Pop (USP) of the SRH" behavior, as defined in "Flavors" (). SRH Max End Pop Type: 42 If the advertised value is zero or no value is advertised, then the router cannot apply PSP or USP flavors.
Maximum H.Encaps MSD Type The Maximum H.Encaps MSD Type signals the maximum number of SIDs that can be added to the segment list of an SRH as part of the "H.Encaps" behavior, as defined in . SRH Max H.encaps Type: 44 If the advertised value is zero or no value is advertised, then the headend can apply an SR Policy that only contains one segment without inserting any SRH header. A non-zero SRH Max H.encaps MSD indicates that the headend can insert an SRH up to the advertised number of SIDs.
Maximum End D MSD Type The Maximum End D MSD Type specifies the maximum number of SIDs present in an SRH when performing decapsulation. As specified in , the permitted SID types include, but are not limited to, End.DX6, End.DT4, End.DT46, End with USD, and End.X with USD. SRH Max End D Type: 45 If the advertised value is zero or no value is advertised, then the router cannot apply any behavior that results in decapsulation and forwarding of the inner packet if the outer IPv6 header contains an SRH.
SRv6 SIDs and Reachability As discussed in , an SRv6 Segment Identifier (SID) is 128 bits and consists of locator, function, and argument parts. A node is provisioned with topology-/algorithm-specific locators for each of the topology/algorithm pairs supported by that node. Each locator is a covering prefix for all SIDs provisioned on that node that have the matching topology/algorithm. Locators MUST be advertised in the SRv6 Locator TLV (see ). Forwarding entries for the locators advertised in the SRv6 Locator TLV MUST be installed in the forwarding plane of receiving SRv6-capable routers when the associated topology/algorithm is supported by the receiving node. The processing of the prefix advertised in the SRv6 Locator TLV, the calculation of its reachability, and the installation in the forwarding plane follows the process defined for the Prefix Reachability TLV 236 or TLV 237 . Locators associated with algorithms 0 and 1 (for all supported topologies) SHOULD also be advertised in a Prefix Reachability TLV (236 or 237) so that legacy routers (i.e., routers that do not support SRv6) will install a forwarding entry for algorithms 0 and 1 SRv6 traffic. In cases where the same prefix with the same prefix length, Multi-Topology Identifier (MTID), and algorithm is received in both a Prefix Reachability TLV and an SRv6 Locator TLV, the Prefix Reachability advertisement MUST be preferred when installing entries in the forwarding plane. This is to prevent inconsistent forwarding entries between SRv6-capable and SRv6-incapable routers. Such preference of Prefix Reachability advertisement does not have any impact on the rest of the data advertised in the SRv6 Locator TLV. Locators associated with Flexible Algorithms (see ) SHOULD NOT be advertised in Prefix Reachability TLVs (236 or 237). Advertising the Flexible Algorithm locator in a regular Prefix Reachability TLV (236 or 237) would make the forwarding for it follow the algorithm 0 path. SRv6 SIDs are advertised as sub-TLVs in the SRv6 Locator TLV, except for SRv6 SIDs that are associated with a specific neighbor/link and are therefore advertised as sub-TLVs in TLVs 22, 23, 25, 141, 222, and 223. SRv6 SIDs received from other nodes are not directly routable and MUST NOT be installed in the forwarding plane. Reachability to SRv6 SIDs depends upon the existence of a covering locator. Adherence to the rules defined in this section will ensure that SRv6 SIDs associated with a supported topology/algorithm pair will be forwarded correctly, while SRv6 SIDs associated with an unsupported topology/algorithm pair will be dropped. NOTE: The drop behavior depends on the absence of a default/summary route covering a given locator. In order for forwarding to work correctly, the locator associated with SRv6 SID advertisements must be the longest match prefix installed in the forwarding plane for those SIDs. In order to ensure correct forwarding, network operators should take steps to make sure that this requirement is not compromised. For example, the following situations should be avoided:
  • Another locator associated with a different topology/algorithm is the longest match.
  • Another prefix advertisement (i.e., from TLV 236 or 237) is the longest match.
Advertising Anycast Property Both prefixes and SRv6 Locators may be configured as anycast; as such, the same value can be advertised by multiple routers. It is useful for other routers to know that the advertisement is for an anycast identifier. A new flag in the Prefix Attribute Flags sub-TLV is defined to advertise the anycast property:
Bit #:
4
Name:
Anycast Flag (A-flag)
When the prefix/SRv6 Locator is configured as anycast, the A-flag SHOULD be set. Otherwise, this flag MUST be clear. The A-flag MUST be preserved when the advertisement is leaked between levels. The A-flag and the N-flag MUST NOT both be set. If both the N-flag and the A-flag are set in the prefix/SRv6 Locator advertisement, the receiving routers MUST ignore the N-flag. The same prefix/SRv6 Locator can be advertised by multiple routers. If at least one of them sets the A-flag in its advertisement, the prefix/SRv6 Locator SHOULD be considered as anycast. A prefix/SRv6 Locator that is advertised by a single node and without an A-flag MUST be considered node specific. All the nodes advertising the same anycast locator MUST instantiate the exact same set of SIDs under that anycast locator. Failure to do so may result in traffic being dropped or misrouted. The Prefix Attribute Flags sub-TLV can be carried in the SRv6 Locator TLV as well as the Prefix Reachability TLVs. When a router originates both the Prefix Reachability TLV and the SRv6 Locator TLV for a given prefix, it SHOULD advertise the Prefix Attribute Flags sub-TLV, if used, in both TLVs and use the same flags. However, unlike TLVs 236 and 237 , the X-flag in the Prefix Attributes Flags sub-TLV is valid when sent in the SRv6 Locator TLV. When included in the Locator TLV, the state of the X-flag in the Prefix Attributes Flags sub-TLV MUST match the setting of the embedded "X-bit" in any advertisement for the same prefix in TLVs 236 and 237 . In case of any inconsistency between the Prefix Attribute Flags advertised in the Locator TLV and in the Prefix Reachability TLV, the ones advertised in the Prefix Reachability TLV MUST be preferred.
Advertising Locators and End SIDs The SRv6 Locator TLV is introduced to advertise SRv6 Locators and End SIDs associated with each locator. This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236, and 237.
SRv6 Locator TLV Format The SRv6 Locator TLV has the following format: 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 |R|R|R|R| MTID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Locator Entries . . . |
Type:
27. Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is variable.
R Bits:
Reserved for future use. They MUST be set to zero on transmission and MUST be ignored on receipt.
MTID:
Multi-Topology Identifier, as defined in . Note that the value 0 is legal.
The SRv6 Locator TLV is followed by one or more locator entries of the form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Algorithm | Loc Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Locator (continued, variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLV-len | Sub-TLVs (variable) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Metric:
4 octets, as described in .
Flags:
1 octet. The following flags are defined: 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |D| Reserved | +-+-+-+-+-+-+-+-+
D-flag: "up/down bit" as described in .
The remaining bits are reserved for future use. They MUST be set to zero on transmission and MUST be ignored on receipt.
Algorithm:
1 octet, as defined in the "IGP Algorithm Types" registry .
Loc-Size:
1 octet. Number of bits in the SRv6 Locator field, which MUST be from the range (1-128). The entire TLV MUST be ignored if the Loc-Size is outside this range.
Locator:
1-16 octets. This field encodes the advertised SRv6 Locator. The SRv6 Locator is encoded in the minimal number of octets for the given number of bits. Trailing bits MUST be set to zero and ignored when received.
Sub-TLV-length:
1 octet. Number of octets used by sub-TLVs.
Optional Sub-TLVs:
Supported sub-TLVs are specified in . Any sub-TLV that is not allowed in the SRv6 Locator TLV MUST be ignored.
The Prefix Attribute Flags sub-TLV SHOULD be included in the Locator TLV. The Prefix Attribute Flags sub-TLV MUST be included in the Locator TLV when it is leaked upwards in the hierarchy or originated as a result of the redistribution from another protocol or another IS-IS instance. If the Prefix Attribute Flags sub-TLV is not included in these cases, receivers will be unable to determine the correct source of the advertisement. The receivers will be unable to detect the violation.
SRv6 End SID Sub-TLV The SRv6 End SID sub-TLV is introduced to advertise SRv6 SIDs with Endpoint behaviors that do not require a particular neighbor in order to be correctly applied. SRv6 SIDs associated with a neighbor are advertised using the sub-TLVs defined in . Supported behavior values, together with parent TLVs in which they are advertised, are specified in of this document. Please note that not all behaviors defined in are defined in this document, e.g., End.T is not. This new sub-TLV is advertised in the SRv6 Locator TLV defined in the previous section. SRv6 End SIDs inherit the topology/algorithm from the parent locator. The SRv6 End SID sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Endpoint Behavior | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (128 bits) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-sub-TLV-len| Sub-sub-TLVs (variable) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
5. Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is variable.
Flags:
1 octet. No flags are currently defined. All bits are reserved for future use. They MUST be set to zero on transmission and MUST be ignored on receipt.
Endpoint Behavior:
2 octets, as defined in . Supported behavior values for this sub-TLV are defined in of this document. Unsupported or unrecognized behavior values are ignored by the receiver.
SID:
16 octets. This field encodes the advertised SRv6 SID.
Sub-sub-TLV-length:
1 octet. Number of octets used by sub-sub-TLVs.
Optional Sub-sub-TLVs:
Supported sub-sub-TLVs are specified in . Any sub-sub-TLV that is not allowed in the SRv6 End SID sub-TLV MUST be ignored.
The SRv6 End SID MUST be allocated from its associated locator. SRv6 End SIDs that are not allocated from the associated locator MUST be ignored. Multiple SRv6 End SIDs MAY be associated with the same locator. In cases where the number of SRv6 End SID sub-TLVs exceeds the capacity of a single TLV, multiple Locator TLVs for the same locator MAY be advertised. For a given MTID/Locator, the algorithm MUST be the same in all TLVs. If this restriction is not met, all TLVs for that MTID/Locator MUST be ignored.
Advertising SRv6 Adjacency SIDs Certain SRv6 Endpoint behaviors are associated with a particular adjacency. This document defines two new sub-TLVs of TLVs 22, 23, 25, 141, 222, and 223 -- namely "SRv6 End.X SID sub-TLVs" and "SRv6 LAN End.X SID sub-TLVs". IS-IS neighbor advertisements are topology specific but not algorithm specific. SIDs advertised in SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs therefore inherit the topology from the associated neighbor advertisement, but the algorithm is specified in the individual SID. All SIDs advertised in SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs MUST be a subnet of a Locator with matching topology and algorithm that are advertised by the same node in an SRv6 Locator TLV. SIDs that do not meet this requirement MUST be ignored. This ensures that the node advertising these SIDs is also advertising its corresponding Locator with the algorithm that will be used for computing paths destined to the SID.
SRv6 End.X SID Sub-TLV This sub-TLV is used to advertise an SRv6 SID associated with a point-to-point adjacency. Multiple SRv6 End.X SID sub-TLVs MAY be associated with the same adjacency. The SRv6 End.X SID sub-TLV has the following format: 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 | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Weight | Endpoint Behavior | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (128 bits) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-sub-tlv-len| Sub-sub-TLVs (variable) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 43.
Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is variable.
Flags:
1 octet. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|S|P|Reserved | +-+-+-+-+-+-+-+-+
where:
B-Flag:
Backup flag. If set, the SID is eligible for protection, e.g., using IP Fast Reroute (IPFRR) , as described in .
S-Flag:
Set flag. When set, the S-flag indicates that the SID refers to a set of adjacencies (and therefore MAY be assigned to other adjacencies as well).
P-Flag:
Persistent flag. When set, the P-flag indicates that the SID is persistently allocated, i.e., the SID value remains consistent across router restart and/or interface flap.
Reserved bits:
Reserved bits MUST be zero when originated and MUST be ignored when received.
Algorithm:
1 octet, as defined in the "IGP Algorithm Types" registry .
Weight:
1 octet. The value represents the weight of the SID for the purpose of load balancing. The use of the weight is defined in [RFC8402].
Endpoint Behavior:
2 octets, as defined in . Supported behavior values for this sub-TLV are defined in of this document. Unsupported or unrecognized behavior values are ignored by the receiver.
SID:
16 octets. This field encodes the advertised SRv6 SID.
Sub-sub-TLV-length:
1 octet. Number of octets used by sub-sub- TLVs.
Optional Sub-sub-TLVs:
Supported sub-sub-TLVs are specified in . Any sub-sub-TLV that is not allowed in SRv6 End.X SID sub-TLV MUST be ignored.
Note that multiple TLVs for the same neighbor may be required in order to advertise all the SRv6 SIDs associated with that neighbor.
SRv6 LAN End.X SID Sub-TLV This sub-TLV is used to advertise an SRv6 SID associated with a LAN adjacency. Since the parent TLV is advertising an adjacency to the Designated Intermediate System (DIS) for the LAN, it is necessary to include the System-ID of the physical neighbor on the LAN with which the SRv6 SID is associated. Given that many neighbors may exist on a given LAN, multiple SRv6 LAN END.X SID sub-TLVs may be associated with the same LAN. Note that multiple TLVs for the same DIS neighbor may be required in order to advertise all the SRv6 SIDs associated with that neighbor. The SRv6 LAN End.X SID sub-TLV has the following format: 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 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Neighbor System-ID (ID length octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Algorithm | Weight | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Endpoint Behavior | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (128 bits) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (cont . . .) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-sub-TLV-len| Sub-sub-TLVs (variable) . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
44. Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is variable.
Neighbor System-ID:
IS-IS System-ID of length "ID Length", as defined in .
Flags:
1 octet. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|S|P|Reserved | +-+-+-+-+-+-+-+-+ The B-, S-, and P-flags are as described in . Reserved bits MUST be zero when originated and MUST be ignored when received.
Algorithm:
1 octet, as defined in the "IGP Algorithm Types" registry .
Weight:
1 octet. The value represents the weight of the SID for the purpose of load balancing. The use of the weight is defined in [RFC8402].
Endpoint Behavior:
2 octets, as defined in . Supported behavior values for this sub-TLV are defined in of this document. Unsupported or unrecognized behavior values are ignored by the receiver.
SID:
16 octets. This field encodes the advertised SRv6 SID.
Sub-sub-TLV-length:
1 octet. Number of octets used by sub-sub- TLVs.
Optional Sub-sub-TLVs:
Supported sub-sub-TLVs are specified in . Any sub-sub-TLV that is not allowed in SRv6 LAN End.X SID sub-TLV MUST be ignored.
Note that multiple TLVs for the same neighbor, on the same LAN, may be required in order to advertise all the SRv6 SIDs associated with that neighbor.
SRv6 SID Structure Sub-Sub-TLV The SRv6 SID Structure sub-sub-TLV is an optional sub-sub-TLV of:
  • SRv6 End SID sub-TLV ()
  • SRv6 End.X SID sub-TLV ()
  • SRv6 LAN End.X SID sub-TLV ()
The SRv6 SID Structure sub-sub-TLV is used to advertise the structure of the SRv6 SID, as defined in . It has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LB Length | LN Length | Fun. Length | Arg. Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type:
1. Single octet, as defined in Section 9 of .
Length:
Single octet, as defined in Section 9 of . The length value is 4 octets.
LB Length:
1 octet. SRv6 SID Locator Block length in bits.
LN Length:
1 octet. SRv6 SID Locator Node length in bits.
Fun. Length:
1 octet. SRv6 SID Function length in bits.
Arg. Length:
1 octet. SRv6 SID Arguments length in bits.
The IS-IS SRv6 SID Structure sub-sub-TLV MUST NOT appear more than once in its parent sub-TLV. If it appears more than once in its parent sub-TLV, the parent sub-TLV MUST be ignored by the receiver. The sum of all four sizes advertised in the IS-IS SRv6 SID Structure sub-sub-TLV MUST be less than or equal to 128 bits. If the sum of all four sizes advertised in the IS-IS SRv6 SID Structure sub-sub-TLV is larger than 128 bits, the parent sub-TLV MUST be ignored by the receiver. The SRv6 SID Structure sub-sub-TLV is intended for informational use by the control and management planes. It MUST NOT be used at a transit node (as defined in ) for forwarding packets. As an example, this information could be used for the following:
  • validation of SRv6 SIDs being instantiated in the network and advertised via IS-IS. These can be learned by controllers via Border Gateway Protocol - Link State (BGP-LS) and then be monitored for conformance to the SRv6 SID allocation scheme chosen by the operator, as described in .
  • verification and automation for securing the SRv6 domain by provisioning filtering rules at SR domain boundaries, as described in .
The details of these potential applications are outside the scope of this document.
Advertising Endpoint Behaviors Endpoint behaviors are defined in . The codepoints for the Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors" registry defined in . If a behavior is advertised, it MUST only be advertised in the TLV(s) marked with "Y" in the table below and MUST NOT be advertised in the TLV(s) marked with "N" in the table below. Endpoint Behaviors
Endpoint Behavior Endpoint Behavior Codepoint End SID End.X SID Lan End.X SID
End (PSP, USP, USD) 1-4, 28-31 Y N N
End.X (PSP, USP, USD) 5-8, 32-35 N Y Y
End.DX6 16 N Y Y
End.DX4 17 N Y Y
End.DT6 18 Y N N
End.DT4 19 Y N N
End.DT46 20 Y N N
IANA Considerations This document requests allocation for the following TLVs, sub-TLVs, and sub-sub-TLVs by updating the existing registries and defining new registries under the "IS-IS TLV Codepoints" grouping.
SRv6 Locator TLV The SRv6 Locator TLV shares sub-TLV space with TLVs advertising prefix reachability. IANA has updated the "IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability" registry initially defined in by adding this document as a reference and updating the description of that registry to include the SRv6 Locator TLV (27). This document makes the following registration in the "IS-IS Top-Level TLV Codepoints" registry: IS-IS Top-Level TLV Codepoints Registry
Value Name IIH LSP SNP Purge
27 SRv6 Locator n y n n
SRv6 End SID Sub-TLV This document makes the following registration: IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability Registry
Type Description 27 135 235 236 237 Reference
5 SRv6 End SID y n n n n RFC 9352,
IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability Registry IANA has updated the "IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability" registry to include a column for the SRv6 Locator TLV (27) as shown below: IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability Registry
Type Description 27 135 235 236 237
1 32-bit Administrative Tag Sub-TLV y y y y y
2 64-bit Administrative Tag Sub-TLV y y y y y
3 Prefix Segment Identifier n y y y y
4 Prefix Attribute Flags y y y y y
6 Flexible Algorithm Prefix Metric (FAPM) n y y y y
11 IPv4 Source Router ID y y y y y
12 IPv6 Source Router ID y y y y y
32 BIER Info n y y y y
SRv6 Capabilities Sub-TLV This document makes the following registration in the "IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV" registry: IS-IS Sub-TLVs for IS-IS Router CAPABILITY TLV Registry
Value Description Reference
25 SRv6 Capabilities RFC 9352,
IS-IS Sub-Sub-TLVs for the SRv6 Capabilities Sub-TLV Registry IANA has created the "IS-IS Sub-Sub-TLVs for SRv6 Capabilities Sub-TLV" registry under the "IS-IS TLV Codepoints" grouping for the assignment of sub-TLV types for the SRv6 Capabilities sub-TLV specified in this document (). This registry defines sub-sub-TLVs for the SRv6 Capabilities sub-TLV (25) advertised in the IS-IS Router CAPABILITY TLV (242). The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . No sub-sub-TLVs are defined by this document, except for the reserved type 0. IS-IS Sub-Sub-TLVs for SRv6 Capabilities Sub-TLV Registry
Value Description Reference
0 Reserved RFC 9532
1-255 Unassigned
SRv6 End.X SID and SRv6 LAN End.X SID Sub-TLVs This document makes the following registrations in the "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information" registry: IS-IS Sub-TLVs for TLVs Advertising Neighbor Information Registry
Type Description 22 23 25 141 222 223 Reference
43 SRv6 End.X SID y y y y y y RFC 9352,
44 SRv6 LAN End.X SID y y y y y y RFC 9352,
MSD Types This document makes the following registrations in the "IGP MSD-Types" registry: IGP MSD-Types
Value Name Reference
41 SRH Max SL RFC 9352
42 SRH Max End Pop RFC 9352
44 SRH Max H.encaps RFC 9352
45 SRH Max End D RFC 9352
IS-IS Sub-Sub-TLVs for SRv6 SID Sub-TLVs Registry IANA has created the "IS-IS Sub-Sub-TLVs for SRv6 SID Sub-TLVs" registry under the "IS-IS TLV Codepoints" grouping to assign sub-TLV types for the SID sub-TLVs specified in this document (Sections , , and ). This registry defines sub-sub-TLVs for SRv6 SID sub-TLVs. This includes the following sub-TLVs:
  • SRv6 End SID (5) (Advertised in SRv6 Locator TLV (27))
  • SRv6 End.X SID (43) (Advertised in TLVs advertising neighbor information)
  • SRv6 LAN End.X SID (44) (Advertised in TLVs advertising neighbor information)
The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . The following assignments are made by this document: IS-IS Sub-Sub-TLVs for SRv6 SID Sub-TLVs Registry
Type Description 5 43 44 Reference
0 Reserved RFC 9352
1 SRv6 SID Structure y y y RFC 9352
2-255 Unassigned
Prefix Attribute Flags Sub-TLV This document adds a new bit in the "IS-IS Bit Values for Prefix Attribute Flags Sub-TLV" registry: IS-IS Bit Values for Prefix Attribute Flags Sub-TLV Registry
Bit # Name Reference
4 Anycast Flag (A-flag) RFC 9352,
IS-IS SRv6 Capabilities Sub-TLV Flags Registry IANA has created the "IS-IS SRv6 Capabilities Sub-TLV Flags" registry under the "IS-IS TLV Codepoints" grouping to assign bits 0 to 15 in the Flags field of the IS-IS SRv6 Capabilities sub-TLV specified in this document (). This registry defines bit values advertised in the Flags field of the SRv6 Capabilities sub-TLV (25). This sub-TLV is advertised in the IS-IS Router CAPABILITY TLV (242). The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . The following assignments are made by this document: IS-IS SRv6 Capabilities Sub-TLV Flags Registry
Type Description Reference
0 Unassigned
1 O-flag RFC 9352,
2-15 Unassigned
IS-IS SRv6 Locator TLV Flags Registry IANA has created the "IS-IS SRv6 Locator TLV Flags" registry under the "IS-IS TLV Codepoints" grouping to assign bits 0 to 7 in the Flags field of the SRv6 Locator TLV specified in this document (). This registry defines bit values advertised in the Flags field of the SRv6 Locator TLV (27). The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . The following assignments are made by this document: IS-IS SRv6 Locator TLV Flags Registry
Value Description Reference
0 D-flag RFC 9352,
1-7 Unassigned
IS-IS SRv6 End SID Sub-TLV Flags Registry IANA has created the "IS-IS SRv6 End SID Sub-TLV Flags" registry under the "IS-IS TLV Codepoints" grouping to assign bits 0 to 7 in the Flags field of the IS-IS SRv6 End SID sub-TLV specified in this document (). This registry defines bit values advertised in the Flags field of the SRv6 End SID sub-TLV (5), which is advertised in the SRv6 Locator TLV (27). The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . No assignments are made by this document. IS-IS SRv6 End SID Sub-TLV Flags Registry
Value Description
0-7 Unassigned
IS-IS SRv6 Adjacency SID Sub-TLVs Flags Registry IANA has created the "IS-IS SRv6 Adjacency SID Sub-TLVs Flags" registry under the "IS-IS TLV Codepoints" grouping to assign bits 0 to 7 in the Flags field of the IS-IS SRv6 End.X SID and LAN End.X SID sub-TLVs (Sections and ). This registry defines bit values advertised in the Flags field of SRv6 SID sub-TLVs associated with adjacencies. These sub-TLVs are advertised in TLVs advertising neighbor information. The list of sub-TLVs includes:
  • SRv6 End.X SID (43)
  • SRv6 LAN End.X SID (44)
The registration procedure is "Expert Review", as defined in . Guidance for the designated experts is provided in . The following assignments are made by this document: IS-IS SRv6 Adjacency SID Sub-TLVs Flags Registry
Value Description Reference
0 B-flag RFC 9352,
1 S-flag RFC 9352,
2 P-flag RFC 9352,
3-7 Unassigned
Security Considerations Security concerns for IS-IS are addressed in , , and . While IS-IS is deployed under a single administrative domain, there can be deployments where potential attackers have access to one or more networks in the IS-IS routing domain. In these deployments, the stronger authentication mechanisms defined in the aforementioned documents SHOULD be used. This document describes the IS-IS extensions required to support SR over an IPv6 data plane. The security considerations for SR are discussed in . defines the SRv6 Network Programming concept and specifies the main SR behaviors to enable the creation of interoperable overlays; the security considerations from that document apply too. The advertisement for an incorrect MSD value may have negative consequences; see for additional considerations. Security concerns associated with the setting of the O-flag are described in . Security concerns associated with the usage of Flexible Algorithms are described in ).
References Normative References Information technology - Telecommunications and information exchange between systems - Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473) International Organization for Standardization Second Edition Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs) This document describes an optional mechanism within Intermediate System to Intermediate Systems (IS-ISs) used today by many ISPs for IGP routing within their clouds. This document describes how to run, within a single IS-IS domain, a set of independent IP topologies that we call Multi-Topologies (MTs). This MT extension can be used for a variety of purposes, such as an in-band management network "on top" of the original IGP topology, maintaining separate IGP routing domains for isolated multicast or IPv6 islands within the backbone, or forcing a subset of an address space to follow a different topology. [STANDARDS-TRACK] IS-IS Extensions for Traffic Engineering This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Traffic Engineering (TE). This document extends the IS-IS protocol by specifying new information that an Intermediate System (router) can place in Link State Protocol Data Units (LSP). This information describes additional details regarding the state of the network that are useful for traffic engineering computations. [STANDARDS-TRACK] Routing IPv6 with IS-IS This document specifies a method for exchanging IPv6 routing information using the IS-IS routing protocol. The described method utilizes two new TLVs: a reachability TLV and an interface address TLV to distribute the necessary IPv6 information throughout a routing domain. Using this method, one can route IPv6 along with IPv4 and OSI using a single intra-domain routing protocol. [STANDARDS-TRACK] Updates to the IS-IS TLV Codepoints Registry This document recommends some editorial changes to the IANA "IS-IS TLV Codepoints" registry to more accurately document the state of the protocol. It also sets out new guidelines for Designated Experts to apply when reviewing allocations from the registry. IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability This document introduces new sub-TLVs to support advertisement of IPv4 and IPv6 prefix attribute flags and the source router ID of the router that originated a prefix advertisement. IS-IS Extensions for Advertising Router Information This document defines a new optional Intermediate System to Intermediate System (IS-IS) TLV named CAPABILITY, formed of multiple sub-TLVs, which allows a router to announce its capabilities within an IS-IS level or the entire routing domain. This document obsoletes RFC 4971. Guidelines for Writing an IANA Considerations Section in RFCs Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Segment Routing Architecture Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. Signaling Maximum SID Depth (MSD) Using IS-IS This document defines a way for an Intermediate System to Intermediate System (IS-IS) router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment ID (SID) stack can be supported in a given network. This document only defines one type of MSD: Base MPLS Imposition. However, it defines an encoding that can support other MSD types. This document focuses on MSD use in a network that is Segment Routing (SR) enabled, but MSD may also be useful when SR is not enabled. OSPF Extensions for Segment Routing Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv2 extensions required for Segment Routing. IS-IS Extensions for Segment Routing Segment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the IS-IS extensions that need to be introduced for Segment Routing operating on an MPLS data plane. IPv6 Segment Routing Header (SRH) Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. Segment Routing over IPv6 (SRv6) Network Programming The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. Operations, Administration, and Maintenance (OAM) in Segment Routing over IPv6 (SRv6) This document describes how the existing IPv6 mechanisms for ping and traceroute can be used in a Segment Routing over IPv6 (SRv6) network. The document also specifies the OAM flag (O-flag) in the Segment Routing Header (SRH) for performing controllable and predictable flow sampling from segment endpoints. In addition, the document describes how a centralized monitoring system performs a path continuity check between any nodes within an SRv6 domain. IGP Flexible Algorithm Informative References Basic Specification for IP Fast Reroute: Loop-Free Alternates This document describes the use of loop-free alternates to provide local protection for unicast traffic in pure IP and MPLS/LDP networks in the event of a single failure, whether link, node, or shared risk link group (SRLG). The goal of this technology is to reduce the packet loss that happens while routers converge after a topology change due to a failure. Rapid failure repair is achieved through use of precalculated backup next-hops that are loop-free and safe to use until the distributed network convergence process completes. This simple approach does not require any support from other routers. The extent to which this goal can be met by this specification is dependent on the topology of the network. [STANDARDS-TRACK] IS-IS Cryptographic Authentication This document describes the authentication of Intermediate System to Intermediate System (IS-IS) Protocol Data Units (PDUs) using the Hashed Message Authentication Codes - Message Digest 5 (HMAC-MD5) algorithm as found in RFC 2104. IS-IS is specified in International Standards Organization (ISO) 10589, with extensions to support Internet Protocol version 4 (IPv4) described in RFC 1195. The base specification includes an authentication mechanism that allows for multiple authentication algorithms. The base specification only specifies the algorithm for cleartext passwords. This document replaces RFC 3567. This document proposes an extension to that specification that allows the use of the HMAC-MD5 authentication algorithm to be used in conjunction with the existing authentication mechanisms. [STANDARDS-TRACK] IS-IS Generic Cryptographic Authentication This document proposes an extension to Intermediate System to Intermediate System (IS-IS) to allow the use of any cryptographic authentication algorithm in addition to the already-documented authentication schemes, described in the base specification and RFC 5304. IS-IS is specified in International Standards Organization (ISO) 10589, with extensions to support Internet Protocol version 4 (IPv4) described in RFC 1195. Although this document has been written specifically for using the Hashed Message Authentication Code (HMAC) construct along with the Secure Hash Algorithm (SHA) family of cryptographic hash functions, the method described in this document is generic and can be used to extend IS-IS to support any cryptographic hash function in the future. [STANDARDS-TRACK] Resiliency Use Cases in Source Packet Routing in Networking (SPRING) Networks This document identifies and describes the requirements for a set of use cases related to Segment Routing network resiliency on Source Packet Routing in Networking (SPRING) networks.
Acknowledgements Thanks to for his review comments and shepherd work. Thanks to and for AD review and comments.
Contributors The following people gave a substantial contribution to the content of this document and should be considered coauthors: Huawei Technologies
stefano@previdi.net
Cisco Systems
Saint Paul Minnesota United States of America pauwells@cisco.com
daniel.voyer@bell.ca
satoru.matsushima@g.softbank.co.jp
bart.peirens@proximus.com
hani.elmalky@ericsson.com
prem@barefootnetworks.com
msharif@barefootnetworks.com
Cisco Systems
Millenium Plaza Building, V Celnici 10, Prague 1 Prague Czech Republic rhanzl@cisco.com
Cisco Systems, Inc.
ketant@cisco.com
Authors' Addresses Cisco Systems
Pribinova Street 10 Bratislava 81109 Slovakia ppsenak@cisco.com
Cisco Systems
Brussels Belgium cfilsfil@cisco.com
Cisco Systems
Milpitas United States of America bashandy@cisco.com
Orange
Chatillon France bruno.decraene@orange.com
Huawei Technologies
huzhibo@huawei.com