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Re: Private ASN suppression

  • From: Tony Mumm
  • Date: Tue May 16 12:54:23 2000


I'm not sure I am looking at this the right way, but:

It seems similar to confederations, but I'm not sure
the stripping method is adequate for becoming a transit AS.

I'm guessing that this was designed for something much
simplier.

The only method I could see, is that a customer is multihomed
to the same AS.   The customer would not likely be able to 
obtain a AS from ARIN since they are fall under the same 
routing policy.  The provider could strip the fake AS, and
announce the prefix with their AS.

Example:

			---------
			|  AS   |
			| 64750 |
			---------
		       /         \
		      /           \
		     /             \
		--------	--------
		| AS X |	| AS X |
		|Site A|	|Site B|
		--------	--------
		    \               /
		     \ 		   /
		      \           /
		       \         /
			----------
			|   The  |
			|Internet|
			----------


AS 64750 announces <64750> up to AS X, AS x uses it to determine
routing policy.  At the edge, AS X will strip it and announce just
<X> to the Internet as a whole.  

AS 64750 would have some control over how the traffic would enter
their network.  This also gives them the mechinism for failover.

I've used this method before, but not in the same exact way.  In
that method, it was a smaller part of a CIDR allocation, so they
were aggregated into a larger block at the edge.  No reason for
the Internet to know about the topology when its all the same
AS anyway.

So, this is only really useful if the customer has their own
blocks.

For cisco to support it...someone has to be using this feature...

(tm)

 "Howard C. Berkowitz" <hcb@clark.net>
    wrote
>
>I'm trying to understand the problem being solved by the Cisco 
>private AS removal feature.  In particular, what advantages does it 
>offer over confederations, which would seem to do the same thing when 
>externally advertising customer routes?  Is there a performance 
>benefit?
>
>RFC1998-style multihoming with a private AS is a possible 
>application, I suppose, for any routes that are NOT marked with 
>NO-EXPORT.







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