The Cidr Report - 4byte ASN handling

Mark Tinka mtinka at
Fri Sep 16 18:11:24 UTC 2011

On Friday, September 16, 2011 07:51:04 AM Schiller, Heather 
A wrote:

> I thought AS-plain notation was the standard for 4-byte
> ASN's?

as-plain is not the "standard" per se. Think of it more as 
the "preferred" option within the industry.

	o All major vendors support it, so there's no need
	  to convert to as-dot when you upgrade your router
	  software to support 4-byte ASN's.

	o as-plain doesn't break your AS_PATH regular
	  expressions, which is very useful.

	o as-plain is a known representation format among
	  operators, and 4-byte ASN's continuing this
	  tradition keeps the network stable.

as-dot notation looks really Cool & Sexy (tm), but is 
cumbersome for your AS_PATH regular expressions. It doesn't 
make things impossible, just, well, cumbersome :-).

Hope this helps.


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