The MPLS WG Archive

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

chetan kumar s wrote:
>
> 	The session attribute object as a flag 'SE Style desired', which
> mandates the egress to respond the resv message with SE style. Now if the
> Path refersh messages have conflicting flags, how is this handled. I was
> looking at the classical RSVP mailing list archive, found an interesting
> thread on this:
> http://www.cs-ipv6.lancs.ac.uk/ipv6/mail-archive/rsvp/1996-04/0068.html

You have one critical mistaken assumption here.  The flags in 
SESSION_ATTRIBUTES are not mandatory.  They are advisory.  An egress 
node is free to ignore them if it wants to.

This should also answer your second question.  If the ingress signals a 
Path requesting SE style, and an SE style Resv is returned, and then the 
ingress refreshes that LSP (or perhaps creates another LSP in the same 
session) without the SE-style request, the egress node should simply 
ignore the change and continue sending back SE-style Resv messages.

Now, if the egress node sends back two different Resv messages with two 
different styles, then the node detecting that conflict should generate 
a ResvErr message.  But this shouldn't happen unless the egress node is 
broken.  A style-conflict error should only happen in a multicast 
situation, where two different egress nodes for the same session choose 
different styles.

-- David