The MPLS WG Archive

[Eric Gray <eric.gray@sandburst.com>]

Sachin,

    I'm not sure what the difference is between the first
question and the second, but the second seems like a
good question.

    A router may be configured to "bridge" certain packets
(e.g. - based on the MAC header).  This used to be called
a "BRouter" in the days before the invention of the term
"L3 Switch".  There are several examples of when this may
need to be done, but a currently applicable one would be in
the VLAN case.  Of course, when a router is configured
this way, it appears like a transparent bridge to frames it
"bridges".  Hence, from the MPLS perspective, it is not
visible to the LSRs between which it may be "bridging"
<L3 packets>-<in MPLS shim>-<in L2 frames>.

    Does this answer your question?

--
Eric Gray

You wrote:

> Can someone answer these:
>
> 1. Is it possible that on a LAN where R1 (router/switch) is connected to
> R3 (router/switch) through R2(router/switch), there is a LSP which has
> only R1 and R3 as LSR's  not R2 (assuming that R1,R2 and R3 all are
> MPLS capable).
>
> 2. If a LSR receives a MPLS packet which was not directed to him (mac DA
> was not this LSR's address), what should it do with the packet? Should
> it switch the packet based on the L2 address or is it allowed to switch
> it based on the MPLS label?
>
> regards,
>    sachin