Private ASNs in the wild

Mark Tinka mark.tinka at
Fri Jan 23 17:50:50 UTC 2015

On Thursday, December 11, 2014 05:55:26 PM ML wrote:

> There are sloppy networks out there.  If it was a big
> enough problem all you'd need is a few key networks drop
> those prefixes and we'd have a...slightly less sloppy
> Internet?

Router software (speaking of Cisco and Juniper in this case) has developed 
reasonably well that one can now strip private ASN's from the AS_PATH 
even though they now appear in between public ASN's.

This was not possible before, as private AS filtering was only possible if 
they appeared contiguously in the AS_PATH.

Of course, this means running later code - but chances are that if you're 
running code that supports 4-byte ASN's, you might have this feature.

Not sure about other vendors out there.

We, for example, remove private ASN's by default on all eBGP sessions. I 
know several other providers that do the same - but it takes a village to 
raise the Internet...

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