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What is multihoming was (design of a real routing v. endpoint id seperation)

  • From: Michael.Dillon
  • Date: Mon Oct 24 05:01:53 2005

> > the market wouldn't
> > feel the need to have to dual home.

> the internet model is to expect and route around failure.

Seems to me that there is some confusion over the meaning
of "multihoming". We seem to assume that it means BGP multihoming
wherein a network is connected to multiple ASes and uses BGP
to manage traffic flows. 

Other people use this term in very different ways. To some people
it means using having multiple IP addresses bound to a single
network interface. To others it means multiple websites on one

And to many consumers of network access it is a synonym for
redundancy or resiliency or something like that. BGP multihoming
is not the only way to satisfy the consumers of network access
and design a solution in which failure is expected and it is
possible for the customer to route around failure.

A single tier-2 ISP who uses BGP multihoming with several
tier 1 ISPs can provide "multihoming" to it's customers 
without BGP. For instance, if this tier-2 has two PoPs
in a city and peering links exist at both PoPs and they
sell a resilient access service where the customer has
two links, one to each PoP, then it is possible to route
around many failures. This is probably sufficient for most
people and if the tier-2 provider takes this service seriously
they can engineer things to make total network collapse exteremely

Another way in which consumer's could be "multihomed" would be 
to have their single access link going to an Internet exchange
where there is a choice of providers. If one provider's network
fails, they could phone up another provider at the exchange and
have a cross-connect moved to restore connectivity in an hour or
so. This will satisfy many people.

Of course there are many variations on the above theme. This is
an issue with multiple solutions, some of which will be superior 
to BGP multihoming. It's not a simple black or white scenario.
And being a tier-1 transit-free provider is not all good. It may
give some people psychological comfort to think that they are in
the number 1 tier, but customers have good reason to see tier-1
transit-free status as a negative.

--Michael Dillon