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Re: 4 Byte AS tested

  • From: Geoff Huston
  • Date: Thu Jan 11 15:22:07 2007

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