Subject: Traditional NLRI not present in UPDATE -- 1771bis and 2858

From: "Howard C. Berkowitz" <[email-masked]>
Date: Sun, 15 Jun 2003 12:06:38 -0400

This is one of those things where I'm feeling that I can't read, that 
the specific point I'm questioning MUST be written down somewhere. 
Nevertheless, here's my question, the specific answer to which I'm 
not finding either in 2858 or Draft 20.

Section 5 of Draft 20 describes conditions on handling legitimate 
UPDATEs when no regular NLRI field is present, but the basic 
description of the UPDATE never says NLRI may not be present. This is 
different than the case where the NLRI field has a length of zero, 
which means it matched all addresses.  Otherwise, I'd say the zero 
length is appropriate to indicate that NLRI deliberately is not 
present.

Am I missing it, or is there no explicit statement that an UPDATE 
need not contain NLRI?

For example, if MULTI-REACH-NLRI is present as an attribute, I assume 
there is no utility to having anything in the regular NLRI field.

I am assuming that Section 4 of 2858 tells how the NLRI is encoded in 
the Type 16/17 attributes, not the NLRI at the end of the UPDATE.

---

From: Mathew Richardson <[email-masked]>
Date: Tue, 17 Jun 2003 14:14:16 -0400

> Howard C. Berkowitz <[email-masked]> [Sun, Jun 15, 2003 at 12:06:38PM -0400]:

<snip>

>Am I missing it, or is there no explicit statement that an UPDATE 

I don't believe there is an explicit statement that the NLRI field is
optional.  In fact, there appears to be at least one sentence that
implies the opposite:

	Reachability information is encoded as one or more 2-tuples of
	the form <length, prefix>, whose fields are described below:

This should probably read:

	Reachability information is encoded as zero or more 2-tuples of
	the form <length, prefix>, whose fields are described below:

Which makes explicit the fact that NLRI does not need to be included.

mrr