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

David Lamparter <> Wed, 29 October 2014 06:28 UTC

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Date: Wed, 29 Oct 2014 07:28:37 +0100
From: David Lamparter <>
To: Brian E Carpenter <>
Message-ID: <20141029062837.GH5186@eidolon>
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Cc: Ole Troan <>, Mikael Abrahamsson <>, "Fred Baker \(fred\)" <>, "" <>, "" <>, David Lamparter <>
Subject: Re: [homenet] dst/src routing drafts (for IETF-91 rtgwg)
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On Wed, Oct 29, 2014 at 08:52:18AM +1300, Brian E Carpenter wrote:
> On 29/10/2014 02:06, Ole Troan wrote:
> > Fred,
> > 
> >>>>
> >>>>
> >> Speaking strictly for myself, I’m not sure why homenet is relevant. The technology is related to networks that have different routing depend on on one’s use case. A class of solutions for it has been called the “fish” problem, and built using multi-topology routing. In homenet, it’s called SADR, and is primarily about egress routing (routing to an egress to an upstream ISP that gave you a PA prefix). While one doesn’t really want to confuse theory with practice, in theory it could be used between points of a network, to prevent folks using one set of prefixes to talk with another set, or to force routing of some sessions in some ways.
> >>
> >> Personally, those are a class of problems I associate with campus networks more than residential networks.
> > 
> > why homenet is relevant?
> > isn't multi-prefix multi-homing one of the most obvious use cases for source address dependent routing? that's not restricted with homenets, but also any small network. I'm assuming large networks will continue with PI addresses and BGP based multihoming.
> If you mean by "large" the few ten thousand largest networks in the
> world, that will not cause significant BGP4 bloat by having PI, then
> yes, I fully agree. Any medium to small network should expect to have
> multiple prefixes in the long run (we are not talking about today, but
> a time when all we old folks who remember the IPv4 world have retired
> and gone fishing).

What I'm personally wondering most in this regard is: to what extent
will larger networks deploy multiple prefixes to the hosts?

I can certainly see it in small to medium businesses that maybe just got
their second uplink at their headquarters and opened 3 shops or
whatever.  But at some point I'd guess policy/enforcement replaces
multiprefix deployments, as Gert wrote in his mail.  Then again, some
shiny new things like MPTCP would benefit from multiprefix deployments,
which might be an argument for some medium-sized users to deploy this?

FWIW, I understand Fred's question for the relevance of homenet as
asking whether these drafts should explicitly target homenet or not, and
I agree that they shouldn't.  Even if 90% of SADR use-cases end up to be
"bread and butter" homenets, the remaining 10% are valid too.