IS-IS Extensions to Support Routing over IPv6 Dataplane

With Segment Routing (SR)[SRARCH], a node steers a packet through an ordered list of instructions, called segments. Segments are identified through Segment Identifiers (SIDs). Segment Routing can be directly instantiated on the IPv6 data plane through the use of the Segment Routing Header defined in [SRH]. SRv6 refers to this SR instantiation on the IPv6 dataplane. The network programming paradigm [NP] is central to SRv6. It describes how any function can be bound to a SID and how any network program can be expressed as a combination of SID's. It defines several well-known functions such as End, End.X, T.Insert, T.Encaps, etc. This document specifies IS-IS extensions that allow IS-IS protocol to encode some of these functions. Familiarity with the network programming paradigm [NP] is necessary to understand the extensions specified in this document. This document defines one new top level IS-IS_TLV and three new IS- IS sub-TLVs. The SRv6 Capabilities sub-TLV announces the ability to support SRv6 and some functions defined in [NP] as well as advertising limitations when applying such functions. The SRv6 SID top level TLV, the P2P SRv6 X-SID sub-TLV, and the LAN SRv6 X-SID sub-TLV are used to advertise which SIDs are instantiated at a node and what function is bound to each instantiated SID. Only ISIS-related functions such as End and its variants D and X [NP] are defined in this document.

As described in [SRH] and [NP], the list of Segments is stored in the segment routing header referred hereafter as "SRH". A router that supports SRv6 MUST be able to process the segment routing header as described in [SRH] and [NP] up to the limitations set by the advertised SRv6-capabilities sub-TLV. To announce this ability, a router uses the newly defined SRv6- capabilities sub-TLV of the router capabilities TLV [RFC7981]. The SRv6- capabilities sub-TLV may contain optional sub-sub-TLVs. The SRv6 Capabilities sub-TLV has the following format:

The following sections define the supported sub-sub-TLVs.

The Maximum Segments Left sub-sub-TLV specifies the maximum value of the "SL" field [SRH] in the SRH of a received packet before applying the function associated with a SID.

The Maximum End Pop SRH sub-sub-TLV specifies the maximum number of SIDs in the top SRH in an SRH stack to which the router can apply "PSP" or USP" [NP] flavors.

The Maximum T.Insert SRH sub-sub-TLV specifies the maximum number of SIDs that can be inserted as part of the "T.insert" behavior [NP].

The Maximum T.Encap SRH sub-sub-TLV specifies the maximum number of SIDs that can be included as part of the "T.Encap" behavior [NP].

The Maximum End D SRH sub-sub-TLV specifies the maximum number of SIDs in an SRH when applying "End.DX6" and "End.DT6" functions.

The SRv6 SID TLV defined in Section 4, P2P SRv6 X-SID sub-TLV specified in Section 6.1, and LAN SRv6 X-SID sub-TLV specified in section 6.2 MUST include one SRv6 function Descriptor. When included in the SRv6 SID TLV, the descriptor is encoded as a sub-TLV. When included in a P2P/LAN SRv6 X-SID sub-TLV, the descriptor is encoded as a sub-sub-TLV. The SRv6-function Descriptor encodes the function (and its flavors) bound to the SRv6 SID advertised in the SRv6 SID TLV [NP]. The SRv6 SID function Descriptor has the following format:

A new top level TLV is introduced to advertise SRv6 Segment Identifiers (SID) and their attributes. The new TLV is used to advertise SRv6 SIDs with any of the functions defined in [NP] whose code point is defined in this document except those SIDs which must be associated with a particular neighbor in order to be correctly applied [NP]. SRv6 SIDs associated with a neighbor are advertised in the sub-TLVs defined in Section 6. This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236 and 237. The SRv6 SID TLV has the following format:

This section defines the code points for supported functions associated with SRv6 SIDs. Functions are defined in [NP]. 0: Reserved 1: End Function 2: End.X Function 3: End.DX6 Function 4: End.DT6 Function

Certain SRv6 functions [NP] must be associated with a particular neighbor, and in case of multiple layer 3 links to the same neighbor, with a particular link in order to be correctly applied. This document specifies how to advertise two such functions in IS- IS, namely End.X and End.DX6 [NP]. SIDs associated with End.X and End.DX6 functions are advertised within neighbor reachability TLVs. This document defines two new sub-TLVs of TLV 22, 23, 222, 223, and 141 - namely "P2P SRv6 X-SID" and "LAN SRv6 X- SID".

This sub-TLV is used to advertise one or more SRv6 SIDs associated with End.X and End.DX6 [NP] functions over a point to point adjacency. The "P2P SRv6 X-SID" sub-TLV has the following format:

The function associated with the advertised SID is specified by the SRv6-Function Descriptor sub-sub-TLV specified in Section 3. If the SRv6-Function Descriptor is encoded in the P2P SRv6 X-SID sub-TLV, then the encoded SRv6 SID function MUST include only the code points of SRv6 SID functions that require the specification of a neighbor to be correctly applied. This document specifies the code points of two such functions, namely End.X and End.DX6 [NP].

This sub-TLV is used to advertise one or more SRv6 SIDs associated with End.X and End.DX6 [NP] functions over a LAN adjacency. The "LAN SRv6 X-SID" sub-TLV has the following format:

This documents request allocation for the following TLVs, sub- TLVs, and sub-sub-TLVs as well updating the ISIS TLV registry and defining a new registry.

This document adds the following new TLV to the IS-IS TLV Codepoints registry. Value: 27 (suggested - to be assigned by IANA) Name: SRv6 SID The name of the "Sub-TLVs for TLVs 135, 235, 236 and 237 registry" needs to be changed to "Sub-TLVs for TLVs 27, 135, 235, 236 and 237 registry". This document adds a new sub-TLV to the (renamed) "Sub-TLVs for TLVs 27, 135, 235, 236 and 237 registry". Value: 5 (Suggested - to be assigned by IANA) Name: SRv6-function Descriptor The revised table of sub-TLVs in the registry should be:

This document requests the creation of a new IANA managed registry to identify SRv6 SID functions. The registration procedure is "Expert Review" as defined in [RFC7370]. Suggested registry name is "SRv6 SID Function Types". A function identifier is an unsigned 8 bit value. The following values are defined by this document: 0 Reserved 1 End function. 2 End.X function 3 End.DX6 function. 4 End.DT6 function.

This document adds the definition of a new sub-TLV in the "Sub- TLVs for TLV 242 registry". Type: 22 (Suggested - to be assigned by IANA) Description: SRv6 Capabilities Thuis document requests the creation of a new IANA managed registry for sub-sub-TLVs of the SRv6 Capability sub-TLV. The registration procedure is "Expert Review" as defined in [RFC7370]. Suggested registry name is "sub-sub-TLVs for SRv6 Capability sub-TLV". The following sub-TLVs are defined by this document: 0: Reserved 1: Max-SL 2: Max-End-Pop-SRH 3: Max-T-Ins-SRH 4: Max-T-Encap-SRH 5: Max-End-D-SR

This document adds the definition of two new sub-TLVs in the "sub- TLVs for TLV 22, 23, 141, 222 and 223 registry". Type: 40 (suggested - to be assigned by IANA) Description: Point-to-Point SRv6 X-SID Type: 41 (suggested - to be assigned by IANA) Description: LAN SRv6 X-SID

This document requests the creation of a new IANA managed registry to identify SRv6 SID functions encoded in P2P/LAN X-SID sub-TLVs. The registration procedure is "Expert Review" as defined in [RFC7370]. Suggested registry name is "SRv6 X-SID sub-sub-TLV Codepoints Registry". The following values are defined by this document: Value: 5 (Suggested - to be assigned by IANA) Name: SRv6-function Descriptor This sub-sub-TLV MAY appear in either the Point-to-Point SRv6 X-SID or the LAN SRv6 X-SID sub-TLVs described in Section 7.4.

Security concerns for IS-IS are addressed in [ISO10589, [RFC5304], and [RFC5310].

The following people gave a substantial contribution to the content of this document and should be considered as co-authors:

Robert Hanzl Cisco Systems Millenium Plaza Building, V Celnici 10, Prague 1, Prague, Czech Republic Email rhanzl@cisco.com ]]>