[spring] Comments on < draft-filsfils-spring-net-pgm-extension-srv6-usid-00>

[Bob Hinden <[e-mail]>]

Hi,

I was looking at < draft-filsfils-spring-net-pgm-extension-srv6-usid-00> and have a few comments.  I am copying the 6MAN list because of its use of IPv6 addresses.

The draft says:

   uSID block: A block of uSID's

      It can be any IPv6 prefix allocated to the provider (e.g. /40 or
      /48), or it can be any block generally available for private use.
      An SR domain may have multiple uSID blocks.

      In this document we leverage FC00::/8 block reserved for private
      use as ULA space (RFC4193).  Throughout this document we use
      FC00::/16 as the illustrated uSID block.  ULA space allows for up
      to 256 uSID blocks in FC00::/8.

The first sentence in the first paragraph is fine, as it is proposing using prefixes assigned to the provider.   The rest is not fine.

ULA space as defined in RFC4193 is not for use like this.   RFC4193 specifies:

   The Local IPv6 addresses are created using a pseudo-randomly
   allocated global ID.  They have the following format:

      | 7 bits |1|  40 bits   |  16 bits  |          64 bits           |
      +--------+-+------------+-----------+----------------------------+
      | Prefix |L| Global ID  | Subnet ID |        Interface ID        |
      +--------+-+------------+-----------+----------------------------+

It is inappropriate to use the a large portion of ULA space (aka FC00::/16) in the manner proposed by this draft.   A better alternative for a provider using SRH is to generate an /48 ULA prefix as defined in RFC4193 and use it for this purpose.  What is proposed in this document will break ULAs for everyone else.

This draft (nor any future drafts in Spring) should not be redefining the IPv6 address space.   It is also very excessive to use this much address space to identify segments in a SRH network.   How many segments are needed to be identified?  Surely not 2^^112.

Regards,
Bob