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Re: TE & SHIM6 (was Re: comments on draft-ietf-shim6-proto-03
On 16-Feb-2006, at 09:39, marcelo bagnulo braun wrote:
Well, i would say that Traffic engineering is about how to
influence routing (i.e. path selection) based on policy considerations
So, as Erik points out above, in the IPv4-BGP-style multihoming, TE
and path selection is performed by changing BGP knobs when
announcing routes. In particular, it is the guy that is configuring
the BGP router the one that will try to influence the path
selection (using stuff like AS path prepending, more specific
routes, MED attributes, communities...). Moreover, because each
direction of the packet flow is influenced by the route
announcement, TE is likely to be set per direction.
OTOH, in the SHIM model, each egress path of the multihomed site is
associated with a given prefix. This basically means that selecting
a prefix of a multihomed host, implies the selection of the path of
the multihomed site used to reach that host. This selection is
performed by the host, so it is up to the host admin to actually
select the path.
I think it's pertinent to note that peer-to-peer traffic in IPv4 is
frequently balanced dynamically by end hosts today (through choice of
I hear about several user-heavy networks who see over 60% of their
traffic from bittorrent, for example. Although I have no science to
promote this as widespread truth, I have yet to find an operator who
measures such things who disagree with me when I mention such a figure.
If we can consider a future in which peer-to-peer traffic increases,
relative to other applications, and in which locality-sensitive peer-
to-peer protocols become more common, then TE looks like it's
naturally shifting to the end hosts anyway; ISPs are left playing an
increasingly futile game of whack-a-mole.
Crippling a multi-homing solution in the interests of preserving a
capability which is increasingly absent does not seem sensible.