Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Hi,

I missed that you referred to "Generalized SRv6 Network Programming for SRv6 Compression". If that's what draft-chen is based on then draft-chen should be extended with relevant (vs. uSID) details, but then a related question is what is the status of that draft in the Spring WG, especially given the ongoing uSID work?

Note that the above does not change the scaling property.

Jeffrey

From: pim <[e-mail]> On Behalf Of Jeffrey (Zhaohui) Zhang
Sent: Sunday, January 24, 2021 11:04 PM
To: Huaimo Chen <[e-mail]>; Stig Venaas <[e-mail]>; [e-mail]
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

[External Email. Be cautious of content]

Hi Huaimo,

The -01 revision is only based on the regular SRv6 SID, not uSID. In my earlier question, I was assuming uSID will be used and your example is also provided with uSID (I think). Even with uSID:


  1.  It takes two IPv6 addresses (256 bits) in SRH (with a 64-bit header itself) in addition to the IPv6 header to encode the 4 leaves with 3 replication points in your example. If uSID is not used then it takes even more bits. I am not convinced that is a scalable solution and I doubt that I am alone.
  2.  The draft needs to be updated with uSID details. For example, whether a uSID block ID is needed in each IPv6 address in the SRH, and when/why padding is needed in the encoding. More questions will come after the details are provided.

Given this, I am even more convinced that that draft is not ready for adoption. It first needs to extended with uSID details and we still need to discuss the scaling property.

Jeffrey

From: Huaimo Chen <[e-mail]<mailto:[e-mail]>>
Sent: Friday, January 22, 2021 5:10 PM
To: Jeffrey (Zhaohui) Zhang <[e-mail]<mailto:[e-mail]>>; Stig Venaas <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

[External Email. Be cautious of content]

Hi Jeffrey,

    Thank you very much for your comments.
    My responses are inline below with prefix [HC].
    The figures for the DA and IPv6 header are attached in .txt file since their formats may be changed below for some email clients.
    BTW, the previous emails with .PDF file could not go through PIM (held since it is too big).

Best Regards,
Huaimo
________________________________
From: pim <[e-mail]<mailto:[e-mail]>> on behalf of Jeffrey (Zhaohui) Zhang <zzhang=[e-mail]<mailto:zzhang=[e-mail]>>
Sent: Friday, January 22, 2021 8:53 AM
To: wangyali <[e-mail]<mailto:[e-mail]>>; Stig Venaas <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Subject: Re: [pim] pim wg adoption call for draft-chen-pim-srv6-p2mp-path-01

I don't see a consensus on this yet on the mailing list.

It would help if a specific illustration of SRv6 header with SRHs to encode the following tree of 4 leaves and 3 replication points (from the draft itself):

                      [L1]                  R Ingress/Root
                      /                    Li Egress/Leaf
                     /                     Pi Transit Node
                    /
                  [P2]------[L2]
                  /
                 /
                /
     [R]------[P1]                [L3]
                \                /
                 \              /
                  \            /
                  [P3]------[P4]------[L4]

            Figure 1: SR P2MP Path from R to L1, L2, L3 and L4

In other words, translate <P1-m, P2-m, P3-m, L1-m, L2-m, P4-m, L3-m, L4-m> into a real IPv6 header with multiple IPv6 addresses in the SRH (using the 40-bit uSID that Huaimo mentioned), and calculate the header size.
[HC]: There are a few of methods for compressing SIDs.
The following is the DA and IPv6 header using G-SRv6 compression method
https://datatracker.ietf.org/doc/draft-cl-spring-generalized-srv6-for-cmpr/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-cl-spring-generalized-srv6-for-cmpr/__;!!NEt6yMaO-gk!TOoWyso7GdxJ13_OcGoZfz7dL0iJ01_zJUmMk9AicZQWhACefd4kuZWppq929ixx$>
for <P1-m, P2-m, P3-m, L1-m, L2-m, P4-m, L3-m, L4-m>.
Node R sends a packet with the IPv6 header to the DA.

Destination Address (DA):
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         2001:db9:0:0 (Common Prefix)                          |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            P1 ID              |       2       |       7       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IPv6 Header:
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Next Header   |  Hdr Ext Len  |  Routing Type | Segments Left |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Last Entry   |      Flags    |              Tag              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            P4 ID              |       2       |       2       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            L3 ID              |       0       |       0       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            L4 ID              |       0       |       0       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Padding                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            P2 ID              |       2       |       2       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            P3 ID              |       1       |       3       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            L1 ID              |       0       |       0       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            L2 ID              |       0       |       0       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

On average, the size u of a compressed SID is 32 bits in this case.


Jeffrey


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