[rbridge] Can we ever have pt-to-pt links?

[Anoop Ghanwani]

> -----Original Message-----
> From: rbridge-bounces at postel.org 
> [mailto:rbridge-bounces at postel.org] On Behalf Of Radia Perlman
> Sent: Monday, November 05, 2007 10:11 PM
> To: Developing a hybrid router/bridge.
> Subject: [rbridge] Can we ever have pt-to-pt links?
> 
> Suppose the topology consisted only of RBridges with pt-to-pt 
> links either to each other or to endnodes, e.g., no bridges, 
> no CSMA/CD. As specified,  we'd wind up creating a pseudonode 
> for each link. Not a total disaster, but it does seem 
> suboptimal, especially if we created a pseudonode for every 
> port that contains an endnode.
> 
> I think we discussed this and said that there was no way of 
> knowing for sure that a port was a pt-to-pt link.

If you were using LLDP, you could be certain that the link
is a point to point link if the system information in LLDP
matches what you receive in the IS-IS hello.  Or you we could
identify RBridges as a type of device in LLDP itself.
 
> Do we want to try to optimize this case, for instance by:

I think it would be useful to optimize.

> a) allowing a port to be configured as "pt-to-pt", and 
> freaking out (as in disabling the port and declaring an 
> error) if an RBridge sees multiple nodes on that port, or sees a BPDU?
> b) assuming if there is only one RBridge neighbors on a port 
> that it is a pt-to-pt link and there does not need to be a 
> pseudonode? That makes me nervous because if a third RBridge 
> comes and goes, then things could get messy.
> c) if there are zero RBridge neighbors on a port (just an 
> endnode or set of endnodes), do not create a pseudonode for it
> d) something else?

Is a combination of (a) and (b) possible?  A node can
either use LLDP to discover it is point to point (and
that won't change as long as the link stays up), or 
it can be manually configured (in which case if a third
adjacency is discovered, then you switch to broadcast-media
mode and once in broadcast-media mode you never switch
back).

> Or is it fine as is (if R1 and R2 are connected with a 
> pt-to-pt link, R1 will get elected DRB, name the link R1.x, 
> and issue two LSPs -- one for R1, one for R1.x, with R1.x 
> claiming connectivity to R1 and R2). Basically, there will be 
> a pseudonode for every RBridge-RBridge link. I hope we don't 
> have to create a pseudonode for every port to every endnode.
> 
> Radia
> _______________________________________________
> rbridge mailing list
> rbridge at postel.org
> http://mailman.postel.org/mailman/listinfo/rbridge
>