The MPLS WG Archive

[John Sparr <johnll44@yahoo.com>]

Hi Bill,

Thanks for the comments. 

I was still a little bit confused about the first
subobject in the ERO. Lets say the example like below:




--- "Sanford, Bill" <bills@netplane.com> wrote:
> 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


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