Subject: RFC2961 clarification

From: "Hong Liao" <[email-masked]>
Date: Thu, 9 Jan 2003 16:38:59 -0500

Hi,

I need the clarification for one issue.

In spec RFC2961, Section 5.2

'Srefresh messages carrying Message_Identifier fields corresponding to Path
state are normally sent with a destination IP address equal to the address
carried in the corresponding SESSION objects.'

Here the destination ip address and source ip address mentioned in the
following paragraph is the one in srefresh ip header or in the Srefresh
Message_Id SRC_LIST, or MESSAGE_ID MCAST_LIST object.

I think it means the source and destination address in the ip header,  can
anyone help me to confirm this?

Thanks,
Julia

---

From: David Charlap <[email-masked]>
Date: Thu, 09 Jan 2003 17:08:07 -0500

> anyone help me to confirm this?

The RFC is correct.  The SESSION address should be the destination, and 
router alert should be used in order to enable the next-hop to intercept 
this message.  This is required for multicast sessions, since the actual 
next-hop addres is unknown.

For the subset of RSVP that is used by MPLS at this time, you may also 
use the next-hop address in the IP header (without router alert.)  Note 
the second half of the paragraph your cited:

	... The destination IP address MAY be set to the RSVP next
	hop when the next hop is known to be RSVP capable and either
	(a) the session is unicast or (b) the outgoing interface is
	a point-to-point link. ...

This should be applicable for most current MPLS implementations.  It may 
actually be applicable to all implementations, since I've never heard of 
any means for running LSPs over broadcast links.

-- David