[rbridge] RBridge: a case of study

[Anoop Ghanwani]

> -----Original Message-----
> From: rbridge-bounces at postel.org 
> [mailto:rbridge-bounces at postel.org] On Behalf Of James Carlson
> Sent: Tuesday, October 30, 2007 2:37 PM
> To: Silvano Gai
> Cc: Developing a hybrid router/bridge.; Radia.Perlman at Sun.COM
> Subject: Re: [rbridge] RBridge: a case of study
> 
> Silvano Gai writes:
> > Radia,
> > 
> > I have added few slides to the example and I suggest that 
> we use it as 
> > a possible case of study for TRILL (of course, not the only one).
> > 
> > Let's see if the solutions we have discussed work on this example.
> > 
> > The complete case of study is at:
> > 
> > http://www.ip6.com/acme-example-v1.ppt
> 
> I have a few narrow questions that I think might help me 
> understand this picture a bit better.  (I probably have more 
> questions once I know the narrow answers.  ;-})

Let me take a shot at answering these.

>   1.  After the proposed fix, should VLAN 3 on Cloud L be bridged
>       together with VLAN 3 on Cloud R, even though the backbone itself
>       doesn't directly carry VLAN 3?  (I.e., are TRILL packets with
>       outer VLAN ID 7 or 8 and with inner VLAN 3 present on the
>       backbone?)

Yes, that's pretty much what ends up happening.  
We have effectively extended the bridged LAN.

>   2.  What happened to the routing that once went on?  It was
>       previously possible to route between these VLANs, but in the new
>       diagram, it's not.  Is routing between these networks
>       unimportant, or does it take place elsewhere, or must RBridges
>       both bridge and route in this scenario?

Routing can continue to happen wherever it was happening.
The Rbridge by itself doesn't do routing, but there's no
reason why one cannot build a device that does bridging,
RBridging, and routing.

>   3.  Suppose we were to configure VLAN 7 within Cloud L.  Would you
>       expect H1 to be able to access nodes within the backbone Cloud G
>       at that point?  (I'm trying to figure out whether the "X" and
>       "Y" interfaces are of fundamentally different types or if the
>       RBridges are just bridges.  I suspect they're different.)

This is where I think would help to introduce some
additional terminology in the spec.  Just like MPLS
LSRs have ingress, core, and egress functionality,
I think we should have similar functions for RBridging.
We could have access ports, trill ports and hybrid
ports.  From access ports, we only accept non-trill
encap'ed frames, from trill ports, we accept only
trill-encap'ed frames, and finally, from hybrid ports
we accept either.  Today we only allow hybrid ports
and perhaps that's OK as a spec.

Anyway, back to the specifics of your question: If you
did configure VLAN 7 within cloud L, then the RBridges
labeled "Router 1" and "Router 2" would have 2 of their
ports configured to be on VLAN 7 and would simply bridge
between those ports.

Anoop