Comments on raft-fz-6man-ipv6-alt-mark-01

[Tom Herbert <[e-mail]>]

Hello,

>From the draft: "Regarding Hop-By-Hop Options Header, if we consider
its real deployment, it is sometimes dropped by legacy devices and not
so used by intermediate nodes.  Destination Options Header is
preferred."

I don't think this is helpful guidance. First of all, it's not just
Hop-by-Hop options that can be dropped, it's pretty much packets with
any extension heades or atypical protocols that might be dropped by
legacy devices-- including packets with Destination Options or Routing
Headers. Neither does it make sense that Destination Options Header is
preferred, as correctly stated in the previous paragraph DO and HBH
address difference use cases (i.e. DO is end to end, and HBH is per
hop). Saying that DO is preferred is equivalent to saying that
end-to-end performance measurements are preferred which I doubt is the
intent. IMO, this whole paragraph could be removed without loss of
content.

"SRH TLV can also be a good choice from this point of view.  The
intermediated nodes that are not in the SID list can consider the SRH
as a green field, they cannot support and bypass or support and dig
into the SRH TLV."

I disagree with the conclusion that SRH TLV is a good choice. The
implicit assumption in this paragraph is that somehow SRH EH is less
likely to be dropped by intermediate nodes than other EH like DO and
HBH. I don't think there's any data to support that. Additionally,
it's not clear what use case an SRH TLV addresses that can't already
be addressed by Destination or HBH options.

Tom