North American Network Operators Group

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RE: multi-homing fixes

  • From: Alex Bligh
  • Date: Sat Aug 25 09:58:34 2001

This would also indicate the
timeframe needed for deployment of software to support 4 byte AS numbers.
FYI, recently issued AS numbers have been in the 22XXX area.
Much of this thread appears to be operating under the flawed assumption
that the only ways to multihome[1] involve inserting prefixes of
some size (under dispute) into the global[2] routing table.

Sure, at the moment, that is predominantly the way things work. But
beyond bitching at eachother about filtering policies (which has
a long record of productive results... mmm...), consider technologies
that can change this.

Well, let's assume the routing table remains static across a failure
(and hence we don't have to introduce prefixes). We need some technology
which acts as an indirection mechanism in the case of a failure.

One such technology possibly ripe for perversion is DNS. Another
is mobile IP. Sure, these may not be great for the application right
now, but they both share a key advantage, which is that the deployer
pays (not the rest of the internet). Assuming the a fixed % of users
multihome (and it's likely to increase), and assuming a fixed cost per
prefix supported (OK, so that's likely to decrease), the costs are
O(n) rather than O(n^2).

And some of these technologies have other advantages. BGP traffic
engineering is difficult (tm), in that it is is almost impossible
to present a list of 2-tuples (correspondant, pipe), and get BGP
to work that way in anything other than the outbound direction,
and dynamic traffic management (responding to congestion) is hard.
Indirected technologies (DNS being an obvious one as it exists,
though it's less than ideal), don't have to suffer the same

[1] = let's define that, for convenience, as to connect to n>1 different
providers of IP connectivity, possibly utilizing redundant tail
circuits, in a manner where if one or more, but not all providers
fail, service is degraded as little as possible.

[2] = less than global, if it becomes balkanized filtering
in response to uncontrolled proliferation of long prefix

Alex Bligh
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