Re: [homenet] dst/src routing drafts (for IETF-91 rtgwg)

David Lamparter <> Wed, 22 October 2014 19:07 UTC

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Date: Wed, 22 Oct 2014 21:06:53 +0200
From: David Lamparter <>
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Cc: "Fred Baker \(fred\)" <>, Mikael Abrahamsson <>
Subject: Re: [homenet] dst/src routing drafts (for IETF-91 rtgwg)
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On Mon, Oct 20, 2014 at 10:40:33PM +0200, David Lamparter wrote:

rtgwg & homenet:

So, these drafts describe the general router behaviour for D/S, without
heading into homenet specifics.  There are a few points that might be
worth going into detail:

- the first draft describes adding random kinds of attributes into route
  lookup.  That's very generic, and it didn't add significant
  complexity, but I don't think we're expecting to insert things in the

- we haven't discussed some of the boundaries to other functions.
  Recursive route handling is unlikely to be relevant for homenet, but
  might warrant feedback from rtgwg.  And the situation is rather
  complex, the draft has an open "multiple-choices TBD" there.

  Interesting for both rtgwg & homenet are behaviour with uRPF filtering
  and multicast RP lookups.  The draft says:
   for uRPF, flip dst & src and match both, if the system supports it.
     If it doesn't, match packet source against all possible route dst.
     (This probably needs better wording in the draft)
   for mcast reverse-path lookup, ignore all D/S routes.  Multicast has
     only (group, source) available, no destination to match against the
     route source prefix.

So, to be explicit on this, D/S routing is conceptually incompatible
with multicast reverse path lookups.  But that can be dealt with (cue to
homenet multicast discussion here.)

Hoping for feedback (including, possibly, "I don't care" or "I have no


P.S.: there is an unfortunate scheduling collision between homenet and
rtgwg for IETF 91... please convert to mail as much as possible!