23456 without AS4_PATH?

Mon Mar 2 18:46:04 UTC 2009

These prefixes all appeared with this problem late last December:
    91.207.218.0/23 35320 196629 23456
   195.128.230.0/24 35320 196629 23456 35748
   195.128.231.0/24 35320 196629 23456 35748

The ill side effects of the AS_CONFED_SEQUENCE in an AS4_PATH and analysis
on what is going on were covered in excellent detail by Andy Davidson,
Jonathan Oddy, and Rob Shakir:
- NANOG thread: http://www.merit.edu/mail.archives/nanog/msg14345.html
- NANOG45 presentation: http://www.nanog.org/meetings/nanog45/presentations/Monday/Davidson_asn4_breaks_light_N45.pdf
- AS4 Wiki: http://as4.cluepon.net/index.php/Operational_Issues#AS_CONFED_SEQUENCE_in_AS4_PATH

Numerous attempts to contact AS 35320's NOC and peering folks about the
problem by several people have pretty much been ignored.

91.196.186.0/24 looks like it just showed up with a broken AS path in the
past couple of days.  We'll probably see it a lot more regular invalid uses
of 23456 in the future... I mean, how often does someone leak a private
ASN :-)?  Perhaps it is a good idea for router and routing software vendors
to add 23456 to "neighbor remove-private-as".

Incidentally, while RFC 4893bis will include better error handling
for 32-bit ASNs, a new I-D to suggest better error handling for
all optional transitive attributes was just released yesterday
(http://www.ietf.org/internet-drafts/draft-scudder-idr-optional-transitive-00.txt).

Greg

-- 
Greg Hankins <ghankins at mindspring.com>
+1 404 542 5530