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

[Radia Perlman]

I'm going to ask on the IS-IS list. Manual configuration is actually 
scarier (and harder) because different
RBridges can be configured differently. With this proposal (the DRB
switches over to pseudonode once there are, say, 3 other RBridges on the 
link, and perhaps
stays that way forever, or until there is ever a time when there is just 
one (or zero) RBridge neighbors.
It's not disruptive to take away the pseudonode when there are very few 
neighbors, since
the coming or going of an RBridge neighbor would require reissuing the 
pseudonode LSP
anyway. So if there were three guys, R1, R2, and R3, with pseudonode 
R1.x, then if
R3 went away, and we kept the pseudonode, then the pseudonode (R1.x) 
would reissue its
LSP saying it now had just two neighbors (R1 and R2), whereas if R1 
decided to
go with "no pseudonode now", then R1 would change its Hello to be "no 
pseudonode",
and R1 and R2 would reissue their LSPs to say their only neighbor was 
eachother (R1 would
remove R1.x as a neighbor and say it is connected to R2....similarly R2).

There is no confusion about whether or not there is a pseudonode because 
the DRB decides.
The exact algorithm for deciding doesn't have to be standardized even, 
though we certainly
should recommend something.

Radia




Russ White wrote:
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>>> The only thing special we were doing with the pseudonode was reporting
>>> the bridge root.
>>> So that means that R1, the DRB, would report the root bridge ID in its
>>> LSP if
>>> R1 has decided not to create a pseudonode.
>>>
>>>       
>> Actually, let me change that to: "Let's always report the root bridge ID
>> in the DRB's
>> LSP, not the pseudonode LSP"
>>
>> So I'm getting more comfortable with that proposal -- the DRB only
>> declares a pseudonode
>> if there really are too many neighbors, and switching over from
>> non-pseudonode to
>> pseudnode is really not very disruptive.
>>     
>
> In most implementations of IS-IS, there is a way to manually configured
> a link as point-to-point, no matter what the layer 2 part of the device
> thinks it is. The IS-IS WG pretty much eschewed auto-detection schemes
> when we went through this exercise.
>
> :-)
>
> Russ
>
> - --
> riw at cisco.com CCIE <>< Grace Alone
>
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