The MPLS WG Archive

[Martin Machacek <m@m3a.cz>]

On Fri, Mar 23, 2001 at 05:19:24PM -0500, Eyad Saheb wrote:
>         I am unclear on the proper IP address to use as IP_DEST in
> RSVP-TE packets, especially when switches are involved.  Unfortunately,
> the "standards" docs aren't too clear on this point (IMHO).  I will
> illustrate my point:
> 
> 1 - 2 - 3 - 4 
>   \        /  
>    5 -----/ 
> 
> In the above topology, if Router 1 wants to establish a path to Router 4
> through 2 & 3 it will create an RSVP-TE packet with IP_DEST = 4 & and
> ERO = 2,3,4.  Correct ? 

Yes.

> This should override the IGP routing table
> which would probably indicate router 5 as the 'correct' next-hop from
> router 1.
> 
> However, consider the following: 
> 
>      +-+ 
>      | |- 2 
>   1 -| |- 3 
>      | |- 4 
>      +-+ 
> 
> In this case, all routers are connected via a switch.  If the same
> RSVP-TE packet is sent over this network, it would reach router 4
> directly.  It would then reject the packet since it'snot the first node
> in the ERO.  Is this expected ?

Well, you are mixing L3 and L2 topology. Your first figure shows L3 (IP)
topology, so lines are links in the IP sense (i.e they can be implemented by any
combination of compatible L2 links - there may be several LAN switchech, ATM
switchech, FrameRelay switches on every link). Your second figure shows L2
topology so lines are links in Ethernet sense (i.e. cables eventually with
repeaters). IP topology of your second figure would look like this:


   1    2    3    4
   |    |    |    |
   ----------------

4 nodes connected to one shared media segment. Nevetheless, assuming that ERO
processing is implemented correctly in all nodes, using the above explicit route
(2,3,4) and target address 4 you should be able to force LSP between 1 and 4 to
traverse 2 and 3 (instead of going directly to 4). Each node should send the
RSVP packet explicitly to the next node in the ERO (by doing L2 address
resolution) instead to node 4 (which is the target and is directly reachable).
Disclaimer: I've tried this setup.

> Was RSVP-TE designed to be run over 'switched' networks ? 

RSVP-TE does not care which L2 topology it runs on. The only requirement is IP
connectivity.


        Martin 

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