The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

Ajay Simha wrote:
>> 
>> CR-LDP has the Path-Vector TLV, which works almost identically to
>> the RSVP RECORD_ROUTE object.
> 
> Good point.  But is it of consequence when one is not using
> Ordered/DoD?

Other modes are only for LDP, not CR-LDP.

But, since you ask, they are also useful in LDP in those modes, but
Path-Vector must now be used in conjunction with hop-count.  Hop-count
will only be non-zero for messages that come from, or are propagated
from, the egress node.  So...

If an ingress node receives a Label Mapping where the hop-count is zero
(unknown), then it the Path-Vector is not a complete path to the
egress.  It represents a partial path through the MPLS cloud, and may
change as the LSP setup is completed.

If it receives a Label Mapping where the hop-count is non-zero, then it
knows that there is a path all the way to the egress, and the
Path-Vector should be an accurate trace of what that path is.

-- David