Subject: [mpls] RFC5036 (LDP) S3.5.3/Pg56, Path Vector Limit in initialization parameters

From: Jeff Wheeler <[email-masked]>
Date: Sun, 9 Dec 2012 01:59:04 -0500

Upon closely reading RFC5036 (LDP) section 3.5.3's description of the
Path Vector Limit communicated in the initialization parameters, I had
some initial confusion.  Perhaps that's just me, or perhaps the
language could be a little more clear.

Specifically, it says, "Although knowledge of a peer's Path Vector
limit will not change an LSR's behavior, it does enable the LSR to
alert an operator to a possible misconfiguration."

My understanding is that, if an LSRu is attached to the LDP domain
with loop detection and it receives Mappings with excessive path
vector length, it would interpret such Mappings as loops, and cause
them to be Released.  Because 3.5.3 allows LSRd to detect this
certainty before sending a Mapping to LSRu, it is saved the effort of
transmitting Mappings that are certain to result in Releases.

The text, "will not change an LSR's behavior," was the cause of my
initial confusion.  Although the LDP domain as a whole will react in a
similarly poor way if LSRu is attached and his PVLim is too small, the
behavior of LSRd is not exactly identical.

My understanding would have been better if the sentence read,
"Knowledge of a peer's Path Vector Limit allows the LSR to alert an
operator to a possible misconfiguration, such as a peer with a PVLim
that is too small for the LDP domain."

I believe those first few words are incorrect and confusing.

-- 
Jeff S Wheeler <[email-masked]>
Sr Network Operator  /  Innovative Network Concepts