The MPLS WG Archive

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

Subhakar K S wrote:
> 
> In RSVP, how does the egress node decide on which
> reservation style to use.

In classical RSVP, there is no way for it to know.  The choice is beyond
the scope of RSVP.

In RSVP-TE, the ingress node can request SE style by setting the
appropriate bit in the SESSION_ATTRIBUTE object.  If this bit is set,
then SE style should be used.  If SESSION_ATTRIBUTE is present and this
bit is not set, then FF style should be used.

If SESSION_ATTRIBUTE is not present, then the switch is free to use
either.

Of course, all of the values in SESSION_ATTRIBUTE are advisory, so an
egress router is free to ignore the bits and choose whatever style it
wants, if there is a good reason to do so.  (Possible reasons include
non-support of one style, explicit local policy.)

-- David