AS Path Loops in practice ?

Niels Bakker niels=nanog at
Tue Dec 9 14:13:12 UTC 2003

* bcrocker at (Ben Crocker) [Tue 09 Dec 2003, 10:44 CET]:
> In our case a customer using BGP to our network from the same AS in two  
> locations but not running an IGP between them (our's is not to reason  
> why and all that)

A commonly accepted definition of AS is as follows:-
| An Autonomous System (AS) is a connected group of one or more IP
| prefixes run by one or more network operators under a *single* and
| clearly defined routing policy.
[emphasis mine]

One cannot have discontiguous networks in the same ASN.  It's pretty
simple: two routing policies, two ASes, two ASNs.  Unfortunately you
weren't able to convince your customer of this.

As you showed, it can be configured.  More power to Vendor J for giving
us all the choice to do so, but that still rarely makes it a good idea.

	-- Niels.

                   the generation that used acid to escape reality
                      is now using antacid to deal with reality

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