[rbridge] Access-only link

[Caitlin Bestler]

I'm not sure if this is the case you are recalling, but Bridges that
are part of a blade chassis, a multi-function NIC, or a hypervisor
soft-bridge all have links (actual or virtual) that are inherently
internal and lead only to known end stations. Doing "discovery" on
those links is overkill.

It is already common to optimize spanning tree based on this knowledge.
Similar optimizations would certainly be done should any of those
bridges take on RBridge functionality. Whether this needs to be
in the standard or not is a separate question. It could easily
fall under the rule that an implementation can do whatever it
wants if it doesn't impact anybody else.


> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org]
On
> Behalf Of Radia Perlman
> Sent: Wednesday, July 09, 2008 10:57 AM
> To: rbridge at postel.org >> "Developing a hybrid router/bridge."
> Subject: [rbridge] Access-only link
> 
> I forget who mentioned to me at the last IETF the desire to have an
> "access only" port. At the time I found it
> scary.
> 
> However, after thinking about it, I've convinced myself it's not
scary,
> and relatively simple to provide.
> 
> We've already added in "trunk only" links, on which data is not
> encapsulated/decapsulated if there happened to
> be endnodes present despite configuration to specify the link as
"trunk
> only". That feature seemed simple to
> provide and useful to me.
> 
> I'm a little less clear on why access-only links are as important,
> since
> it doesn't seem as though the traffic of
> LSP propagation would be that much. But again, I think it's simple and
> safe, so if people think it's useful, I wouldn't
> oppose it.
> 
> The idea is for the DRB to signal in its Hello "this is access-only".
> And in the LSP for the pseudonode, the DRB
> can set the "database overflow" flag, which is a flag already in IS-IS
> for the purpose of dealing with a router that
> can't hold the LSP database. That flag means "don't go through this
> node
> unless absolutely no other path exists".
> If the "overflow" flag is set in the pseudonode's LSP, that would mean
> that that pseudonode would not be computed
> in a path as a transit link.
> 
> Radia
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