Same AS number from different location

Joe Abley jabley at ca.afilias.info
Sun May 25 10:17:55 UTC 2008


On 24 May 2008, at 00:08, devang patel wrote:

> Is that okay to use Same AS number for the two different site on  
> different
> location?

 From the perspective of the rest of the Internet, it will be  
indistinguishable from a topologically-distributed AS with interior  
connectivity, with a different exit policy in different places. So  
yes, it will work.

You should note, though, that in the presence of interior connectivity  
(e.g. a circuit directly between the sites) site A would learn routing  
information about site B internally, and it would not matter that site  
A doesn't hear BGP routes announced to the Internet from site B (in  
fact, that would be a feature). If you have no internal connectivity,  
you might have to think a little harder about that.

I have seen some people  plumb tunnels between their sites to provide  
interior-looking connectivity where none actually exists.

I have seen other people not worry so much, and just point default at  
transit from each place.

> as well as any good documentation or link or deployment scenario  
> where I can
> find the merging of two different AS into one AS?
> As well as what to do if I have an IP addresses as a service provider
> dependent block and want to migrate IP addressing to the IANA  
> assigned ip
> addresses?

I seem to think you'll find presentations about AS consolidation in  
the NANOG meeting archives, somewhere. But basically you join your  
ASes together, start advertising routes from the to-remain AS and drop  
the corresponding routes from the going-away AS, with appropriate  
pauses for checks and breathing.

To renumber, change the addresses on individual things with  
appropriate pauses for DNS TTL expiry. Where changes require  
interaction with customers, good luck and be patient (or drive round  
and change the config on their routers yourself, or give up waiting  
and expect them to get back to you when their net stops working, as  
appropriate).


Joe




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