Re: [Idr] I-D Action: draft-ietf-idr-bgpls-srv6-ext-10.txt

Hi IDRers and Authors,

When read the draft, I find out an issue.

At the beginning, we defined the SRv6 SID as an 128-bit value. In that time, a 128-bit value is the key of the SID in control plane protocol, like IGP/BGP/BGP-LS. Also, a EM lookup can be performed in FIB when forwarding.
But as the development of SRv6, the definition of SRv6 SID has been changed: a SID length may be shorter than 128 bits while the rest bits are padding as zero. And a SID  is presented as a FIB entry which should be hit by a LPM lookup.

"""
   This document defines an SRv6 SID as consisting of LOC:FUNCT:ARG,
   where a locator (LOC) is encoded in the L most significant bits of
   the SID, followed by F bits of function (FUNCT) and A bits of
   arguments (ARG).  L, the locator length, is flexible, and an operator
   is free to use the locator length of their choice.  F and A may be
   any value as long as L+F+A <= 128.  When L+F+A is less than 128, then
   the remaining bits of the SID MUST be zero.
"""

Therefore, the key of the SID in control plane protocols is the prefix with mask not the 128-bit value, and the lookup method should be LPM. Otherwise, errors may come.

For example, 2001:DB8:1:1::/64, and 2001:DB8:1:1:0::/80 can be treated as a single value or the same SID if the receiver identifies a SID by the 128-bit value(same 2001:DB8:1:1::) only without considering the information of the SID structure. But actually, they are two different prefixes that can be allocated to two different SIDs as they are different two prefixes (with two different masks) in the FIB. Considering the SID structure, the same value 2001:DB8:1:1:: with different mask can be treated correctly as two different SIDs.

Therefore, we need to add a mask information/SID structure information to the NLRI.

Similar text is needed in IGP/BGP/PCEP drafts to specify the receiving processing: using the SID value with mask as a key instead of the 128-bit value.

Thanks,
Cheng

-----Original Message-----
From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of internet-drafts@ietf.org
Sent: Friday, September 30, 2022 3:28 AM
To: i-d-announce@ietf.org
Cc: idr@ietf.org
Subject: [Idr] I-D Action: draft-ietf-idr-bgpls-srv6-ext-10.txt

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Inter-Domain Routing WG of the IETF.

        Title           : BGP Link State Extensions for SRv6
        Authors         : Gaurav Dawra
                          Clarence Filsfils
                          Ketan Talaulikar
                          Mach Chen
                          Daniel Bernier
                          Bruno Decraene
  Filename        : draft-ietf-idr-bgpls-srv6-ext-10.txt
  Pages           : 24
  Date            : 2022-09-29

Abstract:
   Segment Routing over IPv6 (SRv6) allows for a flexible definition of
   end-to-end paths within various topologies by encoding paths as
   sequences of topological or functional sub-paths, called "segments".
   These segments are advertised by various protocols such as BGP, IS-IS
   and OSPFv3.

   This document defines extensions to BGP Link-state (BGP-LS) to
   advertise SRv6 segments along with their behaviors and other
   attributes via BGP.  The BGP-LS address-family solution for SRv6
   described in this document is similar to BGP-LS for SR for the MPLS
   data-plane defined in a separate document.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-idr-bgpls-srv6-ext/

There is also an htmlized version available at:
https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgpls-srv6-ext-10

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-idr-bgpls-srv6-ext-10

Internet-Drafts are also available by rsync at rsync.ietf.org::internet-drafts

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