[j-nsp] Mpls

[sthaug at nethelp.no]

> Not sure about first, I'd rather expect it to be null - to change default
> PHP behaviour ie to use value of 0 instead of 3.

"mpls ldp egress-label non-null" is probably related to the change in
default behavior (use PHP by default) that arrived when the M series
MPLS stack was intoduced on the E series. From the 7.2.1 release notes,

http://www.juniper.net/techpubs/software/erx/junose72/sw-rn-erx721/html/sw-rn-erx721-body4.html

"In lower-numbered releases, the egress router always advertised a
real, non-null, label by default. The egress router never requested
that its immediate upstream neighbor perform a penultimate hop pop
(PHP), Instead, the egress router performed an ultimate hop pop by
popping the last label and performing the IP lookup.

In this release, the egress router by default signals the implicit
null label (3) to its upstream neighbor, requesting a PHP. The
upstream neighbor pops the last label and forwards the packet to the
egress router, which then performs only the IP lookup.

You can configure the egress router to perform the old
behavior - sending only real labels upstream - by issuing the mpls
rsvp egress-label non-null command."

Note that this describes "mpls rsvp egress-label non-null" - I assume
"mpls ldp egress-label non-null" is the corresponding command for the
LDP case (though I cannot find this documented).

Steinar Haug, Nethelp consulting, sthaug at nethelp.no