I have reviewed this document as part of the security directorate's 
ongoing effort to review all IETF documents being processed by the 
IESG.  These comments were written primarily for the benefit of the 
security area directors.  Document editors and WG chairs should treat 
these comments just like any other last call comments.

This document reserves the highest-valued 32-bit AS number for an unknown
future use.
>From a security standpoint, since it says don't use it, and doesn't say what
it will be used for in the future, it creates no new security issues. When a
special use is standardized for this AS number, then associated security
risk presumably will be documented.
The document tells operators not to use this reserved value, but tells
implementers they should not consider its use to be a protocol error.
This is equivalent to having a reserved bit in a message format, but this
relates to an IANA registration so needs separate documentation.

I'm a bit surprised the document has an intended status of Informational,
but is being requested in the shepherd writeup to be published as PS or BCP.
Reviewers might assume this only requires the level of review associated
with an Informational doc rather than PS or BCP.

The document is well-written and ready to advance.

David Harrington
ietfdbh at comcast.net
+1-603-828-1401