Re: 4 Byte AS tested

[Geoff Huston <gih () apnic net>]

At 04:59 AM 12/01/2007, Todd Underwood wrote:

> all,
>
> we (renesys) saw as23456 adjacent to both 1221 (expected) and 65001
> (not), originating two prefixes:


that was me, yes :-)

I apologise for the 65001 leak . In mitigation I can only add that it 
did not last very long!




> 203.10.62.0/24
> and
> 203.10.63.0/24
>
> paths looked like:
>
> <peer> 7474 1221 65001 23456 23456 23456
> and many similar
>
> but also
>
> <peer> ... 4637 1221 23456
> and many similar
>
> was the leak of the 65001 as intentional and part of the experiment, a
> simple, error, or is there something useful to learn about the
> difficulties of building filter lists with 4 byte ases?

At the time I needed a 2 byte AS between the OpenBDPD tester and 
AS1221 and I thought it was perhaps less silly to leak a private use 
AS than it was to steal a non-private use AS.

Building filter lists in the 2 byte world to filter out 4 byte paths 
is an issue, as all the 4 byte entries in the path are translated 
into AS23456 when you are in the 2 byte world. This could get tricky 
if you have a complex routing policy that you want to implement and 
some of your policy targets are using 4 byte AS numbers.


regards,

   Geoff