The MPLS WG Archive

[Curtis Villamizar <curtis@workhorse.fictitious.org>]

In message <85256996.006E8048.00@notes949.cc.telcordia.com>, "Hong Liao" writes
:
> 
> 
> Hello,
> 
> >From rsvp-te 07.txt section 2.2,  it says that" Nodes may also modify the ER
> O
> before forwarding the Path message",  I was wondering which way verdors
> implement this since it uses the word "may".
> 
> Thanks in advance.
> 
> Julia


Julia,

Here are some of the ways in which it is modified.

If there is a loose hop the ERO is modified, the CR-SPF lookup is done
and the hop is replaced with one or more strict hop.

If there is a strict hop to a stub advertised by another router or the
router Id (which is also usually advertised as a stub), then the
interface address replaces the stub.

The latter can get you in trouble if the stub is also the far end of
one of your own interfaces, because the intent was usually to take
that interface and no other so the hop should be rejected.

The latter is one of those be conservative in what you send an liberal
in what you accept things and its value is somewhat debatable.  The
former allows loose hop to be used but prevents route loops even if
LSPs are brought up during transient inconsistency in LSDB across
nodes (although a loop could still occur in the future if there is
transient disagreement among LSR over which OSPF area to exit).

Curtis