]> China Mobile

China chengweiqiang@chinamobile.com

Cisco Systems, Inc.

Belgium cf@cisco.com

Huawei Technologies

China lizhenbin@huawei.com

Orange

France bruno.decraene@orange.com

Cisco Systems, Inc.

France fclad.ietf@gmail.com

General SPRING Internet-Draft This document specifies new flavors for the SR segment endpoint behaviors defined in RFC 8986, which enable a compressed SRv6 Segment-List encoding in the Segment Routing Header (SRH).

Introduction The Segment Routing (SR) architecture and SR for IPv6 (SRv6) are defined in . SRv6 Network Programming defines a framework to build a network program with topological and service segments (also referred to by their segment identifier (SID)) carried in a Segment Routing header (SRH) . This document specifies new flavors to the SR segment endpoint behaviors defined in Section 4 of . These flavors enable a compressed encoding of the SRv6 Segment-List in the SRH and therefore address the requirements described in . The flavors defined in this document leverage the SRv6 data plane defined in and , and are compatible with the SRv6 control plane extensions for IS-IS , OSPF , and BGP .

Terminology This document leverages the terms defined in , , and . The reader is assumed to be familiar with this terminology. This document introduces the following new terms: Locator-Block: The SRv6 SID block (IPv6 prefix allocated for SRv6 SIDs by the operator) of an SRv6 SID Locator, as defined in Section 3.1 of . Locator-Node: The identifier of the parent node instantiating a SID in an SRv6 SID Locator, as defined in Section 3.1 of . Compressed-SID (C-SID): The Locator-Node and Function bits of a SID that supports compressed encoding of SIDs. C-SID container: A 128-bit container holding a list of C-SIDs. C-SID sequence: A group of one or more consecutive segment list entries carrying the common Locator-Block and a series of C-SID containers. Uncompressed SID sequence: A group of one or more uncompressed SIDs in a segment list. Compressed Segment List encoding: A segment list encoding that reduces the packet header length thanks to one or more C-SID sequences. A compressed Segment List encoding may also contain any number of uncompressed SID sequences.

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.

Basic Concepts In an SRv6 domain, the SIDs are allocated from a particular IPv6 prefix: the Locator-Block. All SRv6 SIDs instantiated from the same Locator-Block share the same most significant bits. When the combined length of the SRv6 SID Locator, Function, and Argument is smaller than 128 bits, the trailing bits are set to zero. When a sequence of consecutive SIDs in a Segment List shares a common Locator-Block, a compressed Segment-List encoding can optimize the packet header length by avoiding the repetition of the Locator-Block and trailing bits with each individual SID. The compressed Segment List encoding is fully compliant with the specifications in , , and . Efficient encoding is achieved by combining a compressed Segment List encoding logic on the SR source node with new flavors of the base SRv6 endpoint behaviors that decode this compressed encoding. A Segment List can be encoded in the packet header using any combination of compressed and uncompressed sequences. The C-SID sequences leverage the flavors defined in this document, while the uncompressed sequences use behaviors and flavors defined in other documents, such as . An SR source node constructs and compresses the SID-list depending on the capabilities of each SR segment endpoint node that the packet should traverse, as well as its own compression capabilities. It is expected that compressed encoding flavors be available on devices with limited packet manipulation capabilities, such as legacy ASICs. The compressed Segment List encoding supports any Locator-Block allocation. While other options are supported and may provide higher efficiency, each routing domain can be allocated a /48 prefix from a global IPv6 block (see ).

SR Segment Endpoint Flavors This section defines several options to achieve compressed Segment List encoding in the form of two new flavors for the End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, and End.BM behaviors of . These flavors could also be combined with behaviors defined in other documents. The compressed encoding can be achieved by leveraging any of these SR segment endpoint flavors. The NEXT-C-SID flavor and the REPLACE-C-SID flavor expose the same high-level behavior in their use of the SID argument to determine the next segment to be processed, but they have different low-level characteristics that can make one more or less efficient than the other for a particular SRv6 deployment. It is RECOMMENDED, for ease of operation, that a single compressed encoding flavor be used in a given SRv6 domain. However, in a multi-domain deployment, different flavors can be used in different domains. Both flavors leverage the following variables: Variable LBL is the Locator-Block length of the SID. Variable LNFL is the sum of the Locator-Node and the Function lengths of the SID. It is also referred to as C-SID length. Variable AL is the Argument length of the SID.

NEXT-C-SID Flavor A SID instantiated with the NEXT-C-SID flavor takes an argument that carries the remaining C-SIDs in the current C-SID container. The length AL of the argument is equal to 128-LBL-LNFL. An SR segment endpoint node instantiating a SID with the NEXT-C-SID flavor MUST accept any argument value for that SID.

< LNFL > <------------- AL -------------> ]]>

A C-SID sequence using NEXT-C-SID comprises one or more C-SID containers, each carrying the common Locator-Block followed by a series of C-SIDs. The Locator-Node and Function of the C-SID container are those of the first C-SID, and its Argument is the contiguous series of subsequent C-SIDs. When processing a SID with the NEXT-C-SID flavor, while the Argument value is non-zero, the SR segment endpoint node constructs the next SID by copying the SID Argument value immediately after the Locator-Block, thus overwriting the previous SID Locator-Node and Function, and filling the least significant bits of the argument with zeros. When the Argument value is 0, the SR segment endpoint node instead copies the next 128-bit Segment List entry from the SRH to the Destination Address field of the IPv6 header. In both cases, the SR segment endpoint node then forwards the packet to the new destination. The C-SID sequence ends with the last C-SID container.

End with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End SID with the NEXT-C-SID flavor, the procedure described in Section 4.1 of is executed with the following modifications. The below pseudocode is inserted between lines S01 and S02 of the SRH processing in Section 4.1 of , and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of , or prior to processing any extension header other than Hop-by-Hop or Destination Option.

Notes: DA.Argument identifies the bits [(LBL+LNFL)..127] in the Destination Address of the IPv6 header. The value in the Segments Left field of the SRH is not modified when DA.Argument in the received packet has a non-zero value. A rendering of the complete pseudocode is provided in .

End.X with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.X SID with the NEXT-C-SID flavor, the procedure described in Section 4.2 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S08 as shown below.

The resulting pseudocode is inserted between lines S01 and S02 of the SRH processing in Section 4.2 of , and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of , or prior to processing any extension header other than Hop-by-Hop or Destination Option.

End.T with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.T SID with the NEXT-C-SID flavor, the procedure described in Section 4.3 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S08 as shown below.

The resulting pseudocode is inserted between lines S01 and S02 of the SRH processing in Section 4.3 of , and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of , or prior to processing any extension header other than Hop-by-Hop or Destination Option.

End.B6.Encaps with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.B6.Encaps SID with the NEXT-C-SID flavor, the procedure described in Section 4.13 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S08 as shown below.

The resulting pseudocode is inserted between lines S01 and S02 of the SRH processing in Section 4.13 of , and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of , or prior to processing any extension header other than Hop-by-Hop or Destination Option.

End.B6.Encaps.Red with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.B6.Encaps.Red SID with the NEXT-C-SID flavor, the procedure described in Section 4.14 of is executed with the same modifications as in of this document.

End.BM with NEXT-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.BM SID with the NEXT-C-SID flavor, the procedure described in Section 4.15 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S08 as shown below.

The resulting pseudocode is inserted between lines S01 and S02 of the SRH processing in Section 4.15 of , and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of , or prior to processing any extension header other than Hop-by-Hop or Destination Option.

Combination with PSP, USP and USD flavors PSP: The PSP flavor defined in Section 4.16.1 of is unchanged when combined with the NEXT-C-SID flavor. USP: The USP flavor defined in Section 4.16.2 of is unchanged when combined with the NEXT-C-SID flavor. USD: The USD flavor is unchanged when combined with the NEXT-C-SID flavor. The pseudocodes defined in , , and of this document are inserted at the beginning of the modified upper-layer header processing defined in Section 4.16.3 of for End, End.X, and End.T, respectively.

REPLACE-C-SID Flavor A SID instantiated with the REPLACE-C-SID flavor takes an argument that indicates the index of the next C-SID in the appropriate C-SID container. The length AL of the argument is equal to 128-LBL-LNFL. The index value is encoded in the least significant ceil(log_2(128/LNFL)) bits of the argument field.

<---- LNFL ----> <--------- AL ----------> ]]>

A C-SID sequence using REPLACE-C-SID starts with an uncompressed REPLACE-C-SID flavored SID (as shown in ) carrying the common Locator-Block, the Locator-Node and Function of the first C-SID, and an argument with the index value 0. This first SID is copied into the Destination Address field of the IPv6 header either at the SR source node, if it is in the first position in the segment list, or at the previous SR segment endpoint node. The C-SID sequence continues with one or more C-SID containers carrying the subsequent C-SIDs in the sequence. Each container is a 128-bit segment list entry holding a series of C-SIDs without the Locator-Block, as shown in . When processing a SID with the REPLACE-C-SID flavor, the SR segment endpoint node decrements the index value in the SID argument or, if it is 0, instead decrements the Segments Left value in the SRH and resets the index value in the SID argument to the C-SID container capacity minus 1. The updated index value indicates the position of the next C-SID within the C-SID container at the "Segment List" index "Segments Left" in the SRH. The SR segment endpoint node then constructs the next SID by copying this next C-SID immediately after the Locator-Block in the Destination Address field of the IPv6 header, thus overwriting the previous SID Locator-Node and Function. The C-SID sequence ends with a last C-SID in the last C-SID container that does not have the REPLACE-C-SID flavor, or with the special C-SID value 0, or when reaching the end of the segment list, whichever comes first.

<---- LNFL ----> <---- LNFL ----> <---- LNFL ----> ]]>

End with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End SID with the REPLACE-C-SID flavor, the SRH processing described in Section 4.1 of is executed with the following modifications. Line S02 of SRH processing in Section 4.1 of is replaced as follows.

Lines S09 to S16 are replaced by the following pseudo code.

max_LE) or (Segments Left > Last Entry)) { S11. Send an ICMP Parameter Problem to the Source Address, Code 0 (Erroneous header field encountered), Pointer set to the Segments Left field, interrupt packet processing and discard the packet. S12. } S13. Decrement DA.Arg.Index by 1. S14. If (Segment List[Segments Left][DA.Arg.Index] == 0) { S15. Decrement Segments Left by 1. S16. Decrement IPv6 Hop Limit by 1. S17. Update IPv6 DA with Segment List[Segments Left] S18. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. S19. } S20. } Else { S21. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){ S22. Send an ICMP Parameter Problem to the Source Address, Code 0 (Erroneous header field encountered), Pointer set to the Segments Left field, interrupt packet processing and discard the packet. S23. } S24. Decrement Segments Left by 1. S25. Set DA.Arg.Index to (128/LNFL - 1). S26. } S27. Decrement IPv6 Hop Limit by 1. S28. Write Segment List[Segments Left][DA.Arg.Index] into the bits [LBL..LBL+LNFL-1] of the Destination Address of the IPv6 header. S29. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. S30. } ]]>

Notes: DA.Arg.Index identifies the bits [(128-ceil(log_2(128/LNFL)))..127] in the Destination Address of the IPv6 header. Segment List[Segments Left][DA.Arg.Index] identifies the bits [DA.Arg.Index*LNFL..(DA.Arg.Index+1)*LNFL-1] in the SRH Segment List entry at index Segments Left. The upper-layer header processing described in Section 4.1.1 of is unchanged. A rendering of the complete pseudocode is provided in .

End.X with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.X SID with the REPLACE-C-SID flavor, the procedure described in Section 4.2 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S18 and S29 as shown below.

The SRH processing in Section 4.2 of is replaced with the resulting pseudocode. The upper-layer header processing is unchanged.

End.T with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.T SID with the REPLACE-C-SID flavor, the procedure described in Section 4.3 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S18 and S29 as shown below.

The SRH processing in Section 4.3 of is replaced with the resulting pseudocode. The upper-layer header processing is unchanged.

End.B6.Encaps with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.B6.Encaps SID with the REPLACE-C-SID flavor, the procedure described in Section 4.13 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S18 and S29 as shown below.

The SRH processing in Section 4.13 of is replaced with the resulting pseudocode. The upper-layer header processing is unchanged.

End.B6.Encaps.Red with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.B6.Encaps.Red SID with the REPLACE-C-SID flavor, the procedure described in Section 4.14 of is executed with the same modifications as in of this document.

End.BM with REPLACE-C-SID When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.BM SID with the REPLACE-C-SID flavor, the procedure described in Section 4.15 of is executed with the following modifications. The pseudocode in of this document is modified by replacing line S18 and S29 as shown below.

The SRH processing in Section 4.15 of is replaced with the resulting pseudocode. The upper-layer header processing is unchanged.

End.DX and End.DT with REPLACE-C-SID New behaviors of End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, End.DX2U, or End.DX2M with REPLACE-C-SID flavor are also defined in this draft. These new behaviors can be used to indicate the capability of compression of Node and SID, which are required in path computation and compressed SID list encoding. As per , when allocating a C-SID value from a Local Identifiers Block (LIB), an extra prefix of Locator_block:FunctionID::/LBL+FL is required on the Segment Endpoint node to support LIB matching in forwarding. The new behaviors with REPLACE-C-SID flavor explicitly require the node to do so in SID initiation. When processing an IPv6 packet that matches a FIB entry locally instantiated as an End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, End.DT2U or End.DT2M SID with the REPLACE-C-SID flavor, the procedures described in are executed. For End.DT2M with REPLACE-C-SID flavor, when it is used as an uncompressed 128-bit SID, the Arg.FE2 is a 16-bit value located in the significant bits of the argument. When it is used as a C-SID, the Arg.FE2 of the SID is carried in the end of the C-SID sequence. For 16-bit compression, Arg.FE2 is carried in the last 16-bits of the C-SID sequence. For 32-bit compression, Arg.FE2 is carried in the least significant 16 bits of the last 32-bits of the C-SID sequence. When the END.DT2M C-SID and its argument cannot be included in the last container, the SID MUST NOT be compressed and MUST be encoded as a 128-bit uncompressed END.DT2M SID. When processing an IPv6 packet that matches a FIB entry locally instantiated as an END.DT2M with REPLACE-C-SID flavor, the node can obtain the Arg.FE2 from the DA.Argument if DA.Arg.Index is zero, or from the container if DA.Arg.Index is non zero.

Combination with PSP, USP, and USD flavors PSP: When combined with the REPLACE-C-SID flavor, the additional PSP flavor instructions defined in Section 4.16.1.2 of are inserted after line S17 and S28 of the pseudocode in , and the first line of the inserted instructions after S28 is modified as follows.

Note: Segment List[Segments Left][DA.Arg.Index-1] identifies the bits [(DA.Arg.Index-1)*LNFL..DA.Arg.Index*LNFL-1] in the SRH Segment List entry at index Segments Left. USP: When combined with the REPLACE-C-SID flavor, the line S03 of the pseudocode in are substituted by the USP flavor instructions S03.1 to S03.4 defined in Section 4.16.2 of . Note that S03 is shown in the complete pseudocode in . USD: The USD flavor defined in Section 4.16.3 of is unchanged when combined with the REPLACE-C-SID flavor.

C-SID Allocation The C-SID value of 0 is RESERVED. It is used to indicate the end of a C-SID container. In order to efficiently manage the C-SID numbering space, it may be beneficial to divide it into two non-overlapping sub-spaces: a Global Identifiers Block (GIB) and a Local Identifiers Block (LIB). The GIB is the pool of C-SID values available for global allocation. The LIB is the pool of C-SID values available for local allocation. The concept of LIB is applicable to SRv6 and specifically to its NEXT-C-SID and REPLACE-C-SID flavors. The shorter the C-SID, the more benefit the LIB brings. The opportunity to use these sub-spaces, their size, and their C-SID allocation policy depends on the C-SID length relative to the size of the network (e.g., number of nodes, links, service routes). Some guidelines for a typical deployment scenario are provided in .

Global C-SID A C-SID from the GIB. A Global C-SID typically identifies a shortest path to a node in the SRv6 domain. An IP route is advertised by the parent node to each of its global C-SIDs, under the associated Locator-Block. The parent node executes a variant of the End behavior. A node can have multiple global C-SIDs under the same Locator-Block (e.g., one per IGP flexible algorithm). Multiple nodes may share the same global C-SID (anycast).

Local C-SID A C-SID from the LIB. A local C-SID may identify a cross-connect to a direct neighbor over a specific interface or a VPN context. No IP route is advertised by a parent node for its local C-SIDs. If N1 and N2 are two different physical nodes of the SRv6 domain and I is a local C-SID value, then N1 and N2 may bind two different behaviors to I.

C-SID and Locator-Block Length

C-SID Length The NEXT-C-SID flavor supports both 16- and 32-bit C-SID lengths. A C-SID length of 16-bit is RECOMMENDED. The REPLACE-C-SID flavor supports both 16- and 32-bit C-SID lengths. A C-SID length of 32-bit is RECOMMENDED.

Locator-Block Length The RECOMMENDED Locator-Block sizes for the NEXT-C-SID flavor are 16, 32, or 48 bits. The smaller the block length, the higher the compression efficiency. The RECOMMENDED Locator-Block size for the REPLACE-C-SID flavor can be 48, 56, 64, 72, or 80 bits, depending on the needs of the operator.

GIB/LIB Usage GIB and LIB usage is a local implementation and/or configuration decision, however, some guidelines for determining usage for specific SID behaviors and recommendations are provided. The GIB number space is shared among all segment endpoint nodes using SRv6 locators under a Block space. The more SIDs assigned from this space, per node, the faster it is exhausted. Therefore its use is prioritized for global segments, such as SIDs that identify a node. The LIB number space is unique per node. Each node is able to fully utilize the entire LIB number space without consideration of assignments at other nodes. Therefore its use is prioritized for local segments, such as SIDs that identify services (of which there may be many) at nodes, cross-connects, or adjacencies. While a longer C-SID length permits more flexibility in which SID behaviors may be assigned from the GIB, it also reduces the compression efficiency. Given the previous Locator-Block and C-SID length recommendations, the following GIB/LIB usage is RECOMMENDED: NEXT-C-SID: GIB: End LIB: End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V (including large-scale pseudowire), End.B6.Encaps, End.B6.Encaps.Red, End.BM REPLACE-C-SID: GIB: End, End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V, End.B6.Encaps, End.B6.Encaps.Red, End.BM LIB: End.DX2/2V for large-scale pseudowire

Recommended Installation of C-SIDs in FIB An SR segment endpoint node instantiating a NEXT-C-SID or REPLACE-C-SID flavored SID SHOULD install the corresponding FIB entry to match only the Locator and Function parts of the SID (i.e., with a prefix length of LBL + LNL + FL). In addition, an SR segment endpoint node instantiating NEXT-C-SID flavored SIDs from both GIB and LIB MAY install combined "Global + Local" FIB entries to match a sequence of global and local C-SIDs in a single LPM lookup. For example, let us consider an SR segment endpoint node 10 instantiating the following two NEXT-C-SID flavored SIDs according to the C-SID length, Locator-Block length, and GIB/LIB recommendations in this section. 2001:db8:b1:10:: bound to the End behavior with the NEXT-C-SID flavor is instantiated from GIB with Locator-Block length (LBL) = 48 (Locator-Block value 0x20010db800b1), Locator-Node length (LNL) = 16 (Locator-Node value 0x0010), Function length (FL) = 0, and Argument length (AL) = 64. 2001:db8:b1:f123:: bound to the End.X behavior for its local IGP adjacency 123 with the NEXT-C-SID flavor is instantiated from LIB with Locator-Block length (LBL) = 48 (Locator-Block value 0x20010db800b1), Locator-Node length (LNL) = 0, Function length (FL) = 16 (Function value 0xf123), and Argument length (AL) = 64. For SID 2001:db8:b1:10::, Node 10 would install the FIB entry 2001:db8:b1:10::/64 bound the End SID with the NEXT-C-SID flavor. For SID 2001:db8:b1:f123::, Node 10 would install the FIB entry 2001:db8:b1:f123::/64 bound the End.X SID for adjacency 123 with the NEXT-C-SID flavor. In addition, Node 10 may also install the combined FIB entry 2001:db8:b1:10:f123::/80 bound the End.X SID for adjacency 123 with the NEXT-C-SID flavor. As another example, let us consider an SR segment endpoint node 20 instantiating the following two REPLACE-C-SID flavored SIDs according to the C-SID length, Locator-Block length, and GIB/LIB recommendations in this section. 2001:db8:b2:20:1:: from GIB with Locator-Block length (LBL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16, Argument length (AL) = 48, and bound to the End behavior with the REPLACE-C-SID flavor. 2001:db8:b2:20:123:: from GIB with Locator-Block length (LBL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16, Argument length (AL) = 48, and bound to the End.X behavior for its local IGP adjacency 123 with the REPLACE-C-SID flavor. For SID 2001:db8:b2:20:1::, Node 20 would install the FIB entry 2001:db8:b2:20:1::/80 bound the End SID with the REPLACE-C-SID flavor. For SID 2001:db8:b2:20:123::, Node 20 would install the FIB entry 2001:db8:b2:20:123::/80 bound the End.X SID for adjacency 123 with the REPLACE-C-SID flavor.

SR Source Node

Segment Validation An SR source node MUST validate all SIDs defined in this document that it uses as part of a segment list, regardless of whether the segment list is explicitly configured, locally computed, or advertised by a controller (e.g., via BGP or PCEP ). A SID of this document is invalid if associated with an invalid SID structure. The structure of a SID is invalid if any of the following conditions is met. The Locator-Block length is 0. The sum of the Locator-Node length and Function length equals 0. The SID is a Prefix-SID (i.e., bound to the "End" behavior, with any combination of flavors), and the Locator-Node length is 0. The Argument length is different from 128-LBL-LNL-FL. An SR source node MUST NOT include an invalid SID in a segment list. If an explicitly configured or advertised segment list contains an invalid SID, the segment list MUST be declared invalid ().

Segment List Compression An SR source node MAY compress a segment list when it includes NEXT-C-SID and/or REPLACE-C-SID flavor SIDs. If an SR source node chooses to compress the segment list, one method is described below for illustrative purposes. Any other method producing a compressed segment list of equal or shorter length than the uncompressed segment list and resulting in a path equivalent to the uncompressed segment list is compliant. This method walks the uncompressed segment list and compresses each series of consecutive eligible NEXT-C-SID flavored SIDs and each series of consecutive eligible REPLACE-C-SID flavored SIDs. A SID is eligible for compression with this method if all the following conditions are met. The SID behavior has the NEXT-C-SID or the REPLACE-C-SID flavor. The SID is advertised with a SID structure. The SID argument value is 0. When the compression method encounters a series of consecutive eligible NEXT-C-SID or REPLACE-C-SID flavored SIDs, it compresses the series as follows. For a series of NEXT-C-SID flavor SIDs in the uncompressed segment list, an SR source node compresses an uncompressed segment list to a compressed segment list as follows.

For a series of REPLACE-C-SID flavor SIDs of the same C-SID length in the uncompressed segment list, the first segment is not compressed. The SR source node then initializes an empty C-SID container with all bits set to 0 and inserts consecutive C-SIDs from the uncompressed segment list into the container. When the container is full, it is pushed on the compressed segment list and a new container is initialized. For any other SID of uncompressed segment list, it is left uncompressed in the compressed segment list. Regardless of how a compressed segment list is produced, it is encoded in the IPv6 header and optional SRH as described in Section 4.1 and 4.1.1 of . The text is reproduced below for reference.

Rules for NEXT-C-SID flavor uncompressed SID lists If a Destination Option header would follow an SRH with a segment list of more than one segment compressed as a single NEXT-C-SID container, the SR source node MUST NOT omit the SRH. When the last Segment List entry (index 0) in the SRH is a C-SID container representing more than one segment, the PSP operation is performed at the segment preceding the first segment of this C-SID container in the segment list. If the PSP behavior should instead be performed at the penultimate segment along the path, the SR source node MUST NOT compress the ultimate segment of the segment list into a C-SID container. If a Destination Option header would follow an SRH with a last Segment List entry being a NEXT-C-SID container representing more than one segment, the SR source node MUST ensure that the PSP operation is not performed before the penultimate SR segment endpoint node along the path.

Rules for REPLACE-C-SID flavor uncompressed SID lists All REPLACE-C-SID flavor SIDs in a series MUST share the same Locator-Block length (LBL) and the same combined Locator-Node and Function length (LNFL). An uncompressed SID list may contain any number of such series. A series of REPLACE-C-SID flavor SIDs MUST contain at least two elements. End of a C-SID sequence can be indicated by: a SID without REPLACE-C-SID flavor (e.g., End, End.X or NEXT-C-SID flavor End, End.X SID) regardless of the index of the C-SID in the container. The SID MUST have the same Locator-Block and LNFL length as the preceding REPLACE-C-SID flavor SID. a SID with REPLACE-C-SID flavor when the index of the C-SID is greater than 0. The length of a C-SID is determined by its behavior and LNFL. When receiving a 128-bit SID with NEXT-C-SID flavor, LNL=16, FL=16 or 0, AL=128-LBL-NL-FL and the value of argument is all 0, the source node marks the SID supporting 16-bit C-SID. The locator is marked for 16-bit compression. When receiving a 128-bit SID with NEXT-C-SID flavor, LNL= 32, FL=32 or 0, AL=128-LBL-NL-FL and the value of argument is all 0, the source node marks the SID supporting 32-bit C-SID. The locator is marked for 32-bit compression. When receiving a 128-bit SID with REPLACE-C-SID flavor SID, LNL=16, FL= 0, AL=128-LBL-NL-FL and the value of argument is all 0, the source node marks the SID supporting 16-bit C-SID. The locator is marked for 16-bit compression. Other SIDs allocated from this locator can be marked as supporting 16-bit C-SID when LNL=16, FL=16, AL=128-LBL-NL-FL and the value of argument is all 0. When receiving a 128-bit SID with REPLACE-C- SID flavor, LNFL=32, AL=128-LBL-NL-FL and the value of argument is all 0, the source node marks the SID supporting 32-bit C-SID. The locator is marked for 32-bit compression.

Inter Routing Domains with the End.XPS behavior The End.XPS behavior described in this section is OPTIONAL. Some SRv6 traffic may need to cross multiple routing domains, such as different Autonomous Systems (ASes) or different routing areas. Different routing domains may use different addressing schema and Locator-Blocks. This section defines an optional solution and SID behavior allowing for the use of different Locator-Blocks between routing domains. The solution requires a new SID behavior, called "Endpoint with cross-connect to an array of layer-3 adjacencies and SRv6 Prefix Swap" (End.XPS for short) allowing for this transition of Locator-Block between two routing domains. End.XPS is a variant of End.X, performing both "End.X Layer-3 Cross-Connect" and the translation of the Locator-Block between the two routing domains. The processing takes as an additional parameter the prefix B2/m corresponding the Locator-Block in the second domain. This parameter is a property of the (received) SID and is given as a result of the lookup on the IPv6 destination address which identifies the SRv6 SID and its properties. The End.XPS behavior is compatible with the NEXT-C-SID and REPLACE-C-SID flavors described in this document. When a router R receives a packet whose IPv6 DA matches a local End.XPS SID with the NEXT-C-SID flavor, that is associated with a set J of one or more Layer-3 adjacencies and the Locator-Block B2/m of the neighbor routing domain, R processes the packet as follows.

When a router R receives a packet whose IPv6 DA matches a local End.XPS SID with the REPLACE-C-SID flavor, that is associated with a set J of one or more Layer-3 adjacencies and the Locator-Block B2/m of the neighbor routing domain, R processes the packet as follows.

Note: the way the Locator-Block B2 of the next routing domain is known is out of scope of this document. As examples, it could be learnt via configuration, or using a signaling protocol either with the peer domain or with a central controller (e.g. Path Computation Element (PCE)). When End.XPS SID behavior is used, the restriction on the C-SID length for the REPLACE-C-SID flavor is relaxed and becomes: all SID the are part of a C-SID sequence within a domain MUST have the same C-SID length LNFL.

Control Plane This document does not require any new extensions to routing protocols. Section 8 of provides an overview of the control plane protocols used for signaling of the SRv6 SIDs introduced by that document. The SRv6 SIDs introduced by this document are advertised using the same SRv6 extensions for various routing protocols, such as IS-IS OSPFv3 BGP , , , PCEP The SR segment endpoint node MUST set the SID argument bits to 0 when advertising a locally instantiated SID of this document in the routing protocol (e.g., IS-IS , OSPF , or BGP-LS ). Signaling the SRv6 SID Structure is REQUIRED for all the SIDs introduced in this document. It is used by an SR source node to compress a segment list as described in . The length values in the SRv6 SID Structure advertisement MUST match the format of the SID on the SR segment endpoint node. For example, for a SID of this document instantiated from a /48 SRv6 SID block and a /64 Locator, and having a 16-bit Function, the SRv6 SID Structure advertisement carries the following values. Locator-Block length: 48 Locator-Node length: 16 Function length: 16 Argument length: 48 (= 128-48-16-16) A local C-SID MAY be advertised in the control plane individually or in combination with a global C-SID instantiated on the same SR segment endpoint node, with the End behavior, and the same Locator-Block and flavor as the local C-SID. A combined global and local C-SID is advertised as follows. The SID Locator-Block is that shared by the global and local C-SIDs The SID Locator-Node is that of global C-SID The SID Function is that of the local C-SID The SID Argument length is equal to 128-LBL-LNL-FL and the SID Argument value is 0 All other attributes of the SID (e.g., endpoint behavior or algorithm) are those of the local C-SID The local C-SID combined advertisement is needed in particular for control plane protocols mandating that the SID is a subnet of a locator advertised in the same protocol (e.g., Sec. 8 of and Sec. 9 of for advertising Adjacency SIDs in IS-IS and OSPFv3, respectively). For a segment list computed by a controller and signaled to an SR source node (e.g., via BGP or PCEP ), the controller provides the ordered segment list comprising the uncompressed SIDs to the SR source node. The SR source node may then compress the segment list as described in .

Operational Considerations

Ping a SID without a Segment List An SR source node may ping a routable SRv6 SID by sending an ICMPv6 echo request packet destined to the SRv6 SID, as illustrated in Appendix A.1.2 of . When the SRv6 SID in the destination address of the ICMPv6 echo request is one of the SID flavors defined in this document, the SR source node MUST set the arguments of the SID to 0.

Ping a SID via a Segment List An SR source node may ping a routable or non-routable SRv6 SID via a segment list as illustrated in Appendix A.1.2 of . Regardless of the behavior of the SIDs in the SID list, the SR source node computes the ICMP echo request checksum using the ultimate segment in the segment list, i.e., the IPv6 destination address as it is expected to appear at the ultimate destination of the packet.

ICMP Error Processing When an IPv6 node encounters an error while processing a packet, it may report that error by sending an IPv6 error message to the packet source with an enclosed copy of the invoking packet. For the source of an invoking packet to process the ICMP error message, the ultimate destination address of the IPv6 header may be required. Section 5.4 of defines the logic that an SR source node should follow to determine the ultimate destination of an invoking packet containing an SRH. For an SR source node that supports the compressed segment list encoding defined in this document, the logic to determine the ultimate destination is generalized as follows. If the destination address of the invoking IPv6 packet matches a known SRv6 SID, modify the invoking IPv6 packet by applying the SID behavior associated with the matched SRv6 SID; Repeat until the application of the SID behavior would result in the processing of the upper-layer header. The destination address of the resulting IPv6 packet may be used as the ultimate destination of the invoking IPv6 packet. Since the SR source node that needs to determine the ultimate destination is the same node that originally built the segment list in the invoking packet, it is able to perform this operation for all the SIDs in the packet.

Illustrations Illustrations for the functionalities defined in this document are provided in .

Deployment Model Section 5 of defines the intra-SR-domain deployment model and associated security procedures. The same deployment model applies to the SIDs defined in this document.

Implementation Status This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to , "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". This section is provided in compliance with the SPRING working group policies ().

Cisco Systems Cisco Systems reported the following implementations of the SR segment endpoint node NEXT-C-SID flavor () and the SR source node efficient SID-list encoding () for NEXT-C-SID flavored SIDs. These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. Cisco NCS 540 Series routers running IOS XR 7.3.x or above Cisco NCS 560 Series routers running IOS XR 7.6.x or above Cisco NCS 5500 Series routers running IOS XR 7.3.x or above Cisco NCS 5700 Series routers running IOS XR 7.5.x or above Cisco 8000 Series routers running IOS XR 7.5.x or above Cisco ASR 9000 Series routers running IOS XR 7.5.x or above At the time of this report, all the implementations listed above are in production and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the NEXT-C-SID flavor. This report was last updated on January 11, 2023.

Huawei Technologies Huawei Technologies reported the following implementations of the SR segment endpoint node REPLACE-C-SID flavor (). These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. Huawei ATN8XX,ATN910C,ATN980B routers running VRPV800R021C00 or above. Huawei CX600-M2 routers running VRPV800R021C00 or above. Huawei NE40E,ME60-X1X2,ME60-X3X8X16 routers running VRPV800R021C00 or above. Huawei NE5000E,NE9000 routers running VRPV800R021C00 or above. Huawei NCE-IP Controller running V1R21C00 or above. At the time of this report, all the implementations listed above are in production and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the REPLACE-C-SID flavor. This report was last updated on January 11, 2023.

Nokia Nokia reported the following implementations () of the SR segment endpoint node NEXT-C-SID flavor (). These are used as part of its shortest path forwarding (in algorithm 0 and Flex-Algo), remote and TI-LFA repair tunnel, and Traffic Engineering functionalities. Nokia 7950 XRS 20/20e routers running SROS Release 22.10 or above Nokia 7750 SR-12e routers running SROS Release 22.10 or above Nokia 7750 SR-7/12 routers running SROS Release 22.10 or above Nokia 7750 SR-7s/14s routers running SROS Release 22.10 or above Nokia 7750 SR-1/1s/2s routers running SROS Release 22.10 or above At the time of this report, all the implementations listed above are in production and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the NEXT-C-SID flavor. This report was last updated on February 3, 2023.

Arrcus Arrcus reported the following implementations of the SR segment endpoint node NEXT-C-SID flavor (). These are used as part of its SRv6 shortest path forwarding (in algorithm 0 and Flex-Algo), TI-LFA, micro-loop avoidance and Traffic Engineering functionalities. Arrcus running on Ufi Space routers S9510-28DC, S9710-76D, S9600-30DX and S9700-23D with ArcOS v5.2.1 or above Arrcus running n Ufi Space routers S9600-72XC and S9700-53DX with ArcOS v5.1.1D or above Arrcus running on Quanta router IXA and IXAE with ArcOS v5.1.1D or above At the time of this report, all the implementations listed above are in production and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the NEXT-C-SID flavor. This report was last updated on March 11, 2023.

Juniper Networks Juniper Networks reported the following implementations of the SR segment endpoint node NEXT-C-SID flavor (). These are used as part of its SRv6 shortest path forwarding (in algorithm 0 and Flex-Algo), TI-LFA, micro-loop avoidance, and Traffic Engineering functionalities. Juniper release 23.3 onwards supports this functionality. At the time of this report, all the implementations listed above are in development and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the NEXT-C-SID flavor. This report was last updated on May 30, 2023.

Marvell Marvell reported support in the Marvell Prestera Packet Processor for the SR segment endpoint node NEXT-C-SID flavor () and REPLACE-C-SID flavor (). This report was last updated on February 15, 2023.

Broadcom Broadcom reported the following implementations of the SR segment endpoint node NEXT-C-SID flavor () and REPLACE-C-SID flavor (). These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. All implementation of the following list is in general availability for customers using BCM SDK 6.5.26 or above. 88850 (Jericho2c+) series 88690 (Jericho2) series 88800 (Jericho2c) series 88480 (Qunran2a) series 88280 (Qunran2u) series 88295 (Qunran2n) series 88830 (Jericho2x) series At the time of this report, all the implementations listed above are in production and follow the specification in the latest version of this document, including all the "MUST" and "SHOULD" clauses for the NEXT-C-SID and REPLACE-C-SID flavors. For 78900 (Tomahawk) series-related support, please contact the Broadcom team. This report was last updated on February 21, 2023.

ZTE Corporation ZTE Corporation reported the following implementations of the SR segment endpoint node REPLACE-C-SID flavor (). These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. ZTE M6000-18S(BRAS), M6000-8S Plus(BRAS) routers running V5.00.10.09 or above. ZTE M6000-18S(SR), M6000-8S Plus(SR) routers running V5.00.10.80 or above. ZTE T8000-18 routers running V5.00.10.07 or above. This report was last updated on March 29, 2023.

New H3C Technologies New H3C Technologies reported the following implementations of the SR segment endpoint node REPLACE-C-SID flavor (). These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. H3C CR16000-F, SR8800-X routers running Version 7.1.075 or above. H3C CR18000, CR19000 routers running Version 7.1.071 or above. This report was last updated on March 29, 2023.

Ruijie Network Ruijie Network reported the following implementations of the SR segment endpoint node REPLACE-C-SID flavor (). These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. RUIJIE RG-N8018-R, RG-N8010-R routers running N8000-R_RGOS 12.8(3)B0801 or above. This report was last updated on March 29, 2023.

Open Source The authors found the following open source implementations of the SR segment endpoint node NEXT-C-SID flavor (). The Linux kernel, version 6.1 The Software for Open Networking in the Cloud (SONiC), version 202212 , and Switch Abstraction Interface (SAI), version 1.9.0 The Vector Packet Processor (VPP), version 20.05 A generic P4 implementation The authors found the following open source implementations of the SR segment endpoint node REPLACE-C-SID flavor (). ONOS and P4 Programmable Switch based Open SRv6 Project This section was last updated on January 11, 2023.

Interoperability Reports

Bell Canada / Ciena 2023 Bell Canada is currently evaluating interoperability between Ciena and Cisco implementations of the NEXT-C-SID flavor defined in this document. Further information will be added to this section when the evaluation is complete.

EANTC 2023 In April 2023, the European Advanced Networking Test Center (EANTC) successfully validated multiple implementations of SRv6 NEXT-C-SID flavor (a.k.a., SRv6 uSID) . The participating vendors included Arista, Arrcus, Cisco, Huawei, Juniper, Keysight, Nokia, and Spirent.

China Mobile 2020 In November 2020, China Mobile successfully validated multiple interoperable implementations of the NEXT-C-SID and REPLACE-C-SID flavors defined in this document. This testing covered two different implementations of the SRv6 endpoint flavors defined in this document: Hardware implementation in Cisco ASR 9000 running IOS XR Software implementation in Cisco IOS XRv9000 virtual appliance Hardware implementation in Huawei NE40E and NE5000E running VRP The interoperability testing consisted of a packet flow sent by an SR source node N0 via an SR traffic engineering policy with a segment list <S1, S2, S3, S4, S5, S6, S7>, where S1..S7 are SIDs instantiated on SR segment endpoint nodes N1..N7, respectively.

N0 is a generic packet generator. N1, N2, and N3 are Huawei routers. N4, N5, and N6 are Cisco routers. N7 is a generic traffic generator acting as a packet receiver. The SR source node N0 steers the packets onto the SR policy by setting the IPv6 destination address and creating an SRH (as described in Section 4.1 of ) using a compressed segment list encoding. The length of the compressed segment list encoding varies for each scenario. All SR segment endpoint nodes execute a variant of the End behavior: regular End behavior (as defined in Section 4.1 of ), End behavior with NEXT-C-SID flavor, and End behavior with REPLACE-C-SID flavor. The variant being used at each segment endpoint varies for each scenario. The interoperability was validated for the following scenarios: Scenario 1: S1 and S2 are associated with the End behavior with the REPLACE-C-SID flavor S3 is associated with the regular End behavior (no flavor) S4, S5, and S6 are associated with the End behavior with the NEXT-C-SID flavor The SR source node imposes a compressed segment list encoding of 3 SIDs. Scenario 2: S1, S2..., S6 are associated with the End behavior with the NEXT-C-SID flavor The SR source node imposes a compressed segment list encoding of 2 SIDs. Scenario 3: S1, S2..., S6 are associated with the End behavior with the REPLACE-C-SID flavor The SR source node imposes a compressed segment list encoding of 3 SIDs.

Security Considerations The security requirements and mechanisms described in and also apply to this document. This document does not introduce any new security considerations.

IANA Considerations

SRv6 Endpoint Behaviors This I-D. requests the IANA to update the reference of the following registrations from the "SRv6 Endpoint Behaviors" registry under the top-level "Segment Routing" registry-group (https://www.iana.org/assignments/segment-routing/) with the RFC number of this document once it is published, and transfer change control to the IETF. Value Description Reference 43 End with NEXT-CSID This I-D. 44 End with NEXT-CSID & PSP This I-D. 45 End with NEXT-CSID & USP This I-D. 46 End with NEXT-CSID, PSP & USP This I-D. 47 End with NEXT-CSID & USD This I-D. 48 End with NEXT-CSID, PSP & USD This I-D. 49 End with NEXT-CSID, USP & USD This I-D. 50 End with NEXT-CSID, PSP, USP & USD This I-D. 52 End.X with NEXT-CSID This I-D. 53 End.X with NEXT-CSID & PSP This I-D. 54 End.X with NEXT-CSID & USP This I-D. 55 End.X with NEXT-CSID, PSP & USP This I-D. 56 End.X with NEXT-CSID & USD This I-D. 57 End.X with NEXT-CSID, PSP & USD This I-D. 58 End.X with NEXT-CSID, USP & USD This I-D. 59 End.X with NEXT-CSID, PSP, USP & USD This I-D. 85 End.T with NEXT-CSID This I-D. 86 End.T with NEXT-CSID & PSP This I-D. 87 End.T with NEXT-CSID & USP This I-D. 88 End.T with NEXT-CSID, PSP & USP This I-D. 89 End.T with NEXT-CSID & USD This I-D. 90 End.T with NEXT-CSID, PSP & USD This I-D. 91 End.T with NEXT-CSID, USP & USD This I-D. 92 End.T with NEXT-CSID, PSP, USP & USD This I-D. 93 End.B6.Encaps with NEXT-CSID This I-D. 94 End.B6.Encaps.Red with NEXT-CSID This I-D. 95 End.BM with NEXT-CSID This I-D. 101 End with REPLACE-CSID This I-D. 102 End with REPLACE-CSID & PSP This I-D. 103 End with REPLACE-CSID & USP This I-D. 104 End with REPLACE-CSID, PSP & USP This I-D. 105 End.X with REPLACE-CSID This I-D. 106 End.X with REPLACE-CSID & PSP This I-D. 107 End.X with REPLACE-CSID & USP This I-D. 108 End.X with REPLACE-CSID, PSP & USP This I-D. 109 End.T with REPLACE-CSID This I-D. 110 End.T with REPLACE-CSID & PSP This I-D. 111 End.T with REPLACE-CSID & USP This I-D. 112 End.T with REPLACE-CSID, PSP & USP This I-D. 114 End.B6.Encaps with REPLACE-CSID This I-D. 115 End.BM with REPLACE-CSID This I-D. 116 End.DX6 with REPLACE-CSID This I-D. 117 End.DX4 with REPLACE-CSID This I-D. 118 End.DT6 with REPLACE-CSID This I-D. 119 End.DT4 with REPLACE-CSID This I-D. 120 End.DT46 with REPLACE-CSID This I-D. 121 End.DX2 with REPLACE-CSID This I-D. 122 End.DX2V with REPLACE-CSID This I-D. 123 End.DT2U with REPLACE-CSID This I-D. 124 End.DT2M with REPLACE-CSID This I-D. 127 End.B6.Encaps.Red with REPLACE-CSID This I-D. 128 End with REPLACE-CSID & USD This I-D. 129 End with REPLACE-CSID, PSP & USD This I-D. 130 End with REPLACE-CSID, USP & USD This I-D. 131 End with REPLACE-CSID, PSP, USP & USD This I-D. 132 End.X with REPLACE-CSID & USD This I-D. 133 End.X with REPLACE-CSID, PSP & USD This I-D. 134 End.X with REPLACE-CSID, USP & USD This I-D. 135 End.X with REPLACE-CSID, PSP, USP & USD This I-D. 136 End.T with REPLACE-CSID & USD This I-D. 137 End.T with REPLACE-CSID, PSP & USD This I-D. 138 End.T with REPLACE-CSID, USP & USD This I-D. 139 End.T with REPLACE-CSID, PSP, USP & USD This I-D.

Acknowledgements The authors would like to thank Kamran Raza, Xing Jiang, YuanChao Su, Han Li, Yisong Liu, and Martin Vigoureux for their insightful feedback and suggestions.

&RFC8402; &RFC8754; &RFC8986; &RFC2119; &RFC8174; &RFC7942; &RFC9252; &RFC9256; &RFC9259; &RFC9352; &I-D.ietf-lsr-ospfv3-srv6-extensions; &I-D.ietf-idr-bgpls-srv6-ext; &I-D.ietf-idr-bgp-ls-sr-policy; &I-D.ietf-idr-segment-routing-te-policy; &I-D.ietf-pce-segment-routing-ipv6; &I-D.clad-spring-srv6-srh-compression-illus; &I-D.srcompdt-spring-compression-requirement; SPRING Working Group Chairs Cisco Systems Cisco Systems Cisco Systems Cisco Systems Cisco Systems Cisco Systems Nokia FD.io Open Networking Foundation European Advanced Networking Test Center (EANTC)

Open Issues This section was added as requested by the SPRING chair in . Issues raised during and after the adoption call for this draft are tracked in an issue tracker. The remainder of this section identifies the most significant open issues, from the adoption call, for the working group to keep track of. As a reminder to those reading this section, this document is a work in progress, and subject to change by the working group. As noted at the front of this document, "It is inappropriate to use Internet-Drafts as reference material" Given that the working group has said that it wants to standardize one data plane solution, and given that the document contains multiple SRv6 EndPoint behaviors that some WG members have stated are multiple data plane solutions, the working group will address whether this is valid and coherent with its one data plane solution objective. As reminded in the conclusion of the adoption call, this document is subject to the policy announced by the SPRING chairs in . In particular, this means that this document can not go to WG last call until 6man completes handling of an Internet Draft that deals with the relationship of C-SIDs to RFC 4291. It is hoped and expected that said resolution will be a WG last call and document approval in 6man of a document providing for the way that C-SIDs use the IPv6 destination address field.

Complete pseudocodes The content of this section is purely informative rendering of the pseudocodes of with the modifications in this document. This rendering may not be used as a reference.

End with NEXT-C-SID When processing the SRH of a packet matching a FIB entry locally instantiated as an End SID with the NEXT-C-SID flavor:

max_LE) or (Segments Left > Last Entry+1)) { S18. Send an ICMP Parameter Problem to the Source Address with Code 0 (Erroneous header field encountered) and Pointer set to the Segments Left field, interrupt packet processing, and discard the packet. S19. } S20. Decrement IPv6 Hop Limit by 1. S21. Decrement Segments Left by 1. S22. Update IPv6 DA with Segment List[Segments Left]. S23. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. ]]>

Before processing the Upper-Layer header or any IPv6 extension header other than Hop-by-Hop or Destination Option of a packet matching a FIB entry locally instantiated as an End SID with the NEXT-C-SID flavor:

When processing the Upper-Layer header of a packet matching a FIB entry locally instantiated as an End SID with the NEXT-C-SID flavor:

End with REPLACE-C-SID When processing the SRH of a packet matching a FIB entry locally instantiated as an End SID with the REPLACE-C-SID flavor:

max_LE) or (Segments Left > Last Entry)) { S11. Send an ICMP Parameter Problem to the Source Address, Code 0 (Erroneous header field encountered), Pointer set to the Segments Left field, interrupt packet processing and discard the packet. S12. } S13. Decrement DA.Arg.Index by 1. S14. If (Segment List[Segments Left][DA.Arg.Index] == 0) { S15. Decrement Segments Left by 1. S16. Decrement IPv6 Hop Limit by 1. S17. Update IPv6 DA with Segment List[Segments Left] S18. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. S19. } S20. } Else { S21. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){ S22. Send an ICMP Parameter Problem to the Source Address, Code 0 (Erroneous header field encountered), Pointer set to the Segments Left field, interrupt packet processing and discard the packet. S23. } S24. Decrement Segments Left by 1. S25. Set DA.Arg.Index to (128/LNFL - 1). S26. } S27. Decrement IPv6 Hop Limit by 1. S28. Write Segment List[Segments Left][DA.Arg.Index] into the bits [LBL..LBL+LNFL-1] of the Destination Address of the IPv6 header. S29. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. S30. } ]]>

When processing the Upper-Layer header of a packet matching a FIB entry locally instantiated as an End SID with the REPLACE-C-SID flavor:

Contributors ZTE Corporation

China liu.aihua@zte.com.cn

Alibaba

USA d.cai@alibaba-inc.com

Cisco Systems, Inc.

Canada ddukes@cisco.com

Futurewei Technologies Ltd.

USA james.n.guichard@futurewei.com

Huawei Technologies

China c.l@huawei.com

NTT Network Innovations

USA robert@raszuk.net

Cisco Systems, Inc.

India ketant.ietf@gmail.com

Bell Canada

Canada daniel.voyer@bell.ca

Broadcom

Israel shay.zadok@broadcom.com