The MPLS WG Archive

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

Eyad Saheb wrote:
> 
> Hello,
> 
> 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 ?  This should override the IGP
> routing table which would probably indicate router 5 as the 'correct'
> next-hop from router 1.

Yes.

> 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 ?

as Martin wrote, you're confusing layer-2 with layer-3.

In this topology, router 1 should send the Path message to 2, which will
then send it to 3, which will then send it to 4.  As per the ERO.  The
fact that 1 is directly conneted to 4 changes nothing.

1 will use 2 as it's next-hop router, and therefore will use 2's
Ethernet address when sending the packet.  The fact that the routing
table shows 4 as the next hop on the shortest path doesn't matter - an
ERO is supposed to override the routing table.

-- David