The MPLS WG Archive

["Sanford, Bill" <bills@netplane.com>]

John, see the comments below:

> -----Original Message-----
> From: John Sparr [mailto:johnll44@yahoo.com]
> Sent: Tuesday, January 02, 2001 3:43 PM
> To: mpls@UU.NET
> Subject: ERO and strict/loose subobject
> 
> 
> Hi all,
> 
> One question about the ERO object in RSVP:
> 
> Assuming there is a sender node and it creates an ERO.
> Should the ERO include the ip address of sender
> itself? If yes, why?

Lets say the ERO is not set with the sender node and is started on the next
hop.  How does the LSP you want to set up know that there are no other hops
in between the sender and next hop?  If you don't have the senders ip
address as the first subobject, there isn't any way to set the properties of
the link to the next hop to loose or strict.

In the implementation in draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, if you
didn't have the sender address in the ERO, it would immediately error with
"Bad EXPLICIT_ROUTE object" error.

In 4.3.4.1. Selection of the Next Hop, it explains:

1) The node receiving the RSVP message MUST first evaluate the first
   subobject.  If the node is not part of the abstract node described by
   the first subobject, it has received the message in error and SHOULD
   return a "Bad initial subobject" error.  If there is no first
   subobject, the message is also in error and the system SHOULD return
   a "Bad EXPLICIT_ROUTE object" error.

> 
> Another question is about strict/loose object:
> 
> The draft of RSVP-TE says "The path between a strict
> node and its preceding node MUST include only network
> nodes from the strict node and its preceding abstract
> node."
> 
> Does it mean if there is strict subobject in ERO, then
> ther is no loose subobject and if there is loose
> subobject, then there is no strict subobject?

Not at all.  You can have both strict hops and loose hops as part of the
same ERO.  On a "strict" hop link, there isn't any other route it can take
except for the next hop in the ERO list.  On a "loose" hop link, there can
be additional hops between the nodes provided that it ends up on the next
hop.

Bill