[rbridge] Proposed details for announcing endnodes

[Joe Touch]

Steve Dalberg wrote:
>> Radia Perlman wrote:
>>> Yeah. Moving endnodes is always an issue. Even with bridges. The 
>>> problem with having R1 (the one announcing that endnode E 
>> is attached 
>>> to R1) having a very short learning cache is that makes 
>> R1's endnode 
>>> announcement LSP information annoyingly volatile. The 
>> problem with the 
>>> learning cache timer being long is that R1 can be a black hole, 
>>> sucking traffic away from where E really is.
>>>
>>> There are some layer 2 protocols, I believe, with explicit 
>>> registration and keep-alives. (anyone care to chime in about which 
>>> protocols these are?). Endnodes learned that way are good 
>> candidates 
>>> for explicitly advertising.
>>>
>>> For attached IP endnodes, R1 could do something like, if it seems 
>>> someone else advertise E, R1 could do an ARP to see if E is still 
>>> there. And there might be similar purely layer 2 "pings". 
>> (are there?)
>>
>> I do not believe rbridges should ever issue ARPs. Silent 
>> movement is a known problem with existing bridges; this is 
>> not an issue we should be solving.
>>
>> Joe
> 
> I agree, although from a protocol level, what is the fallout from
> conflicting MAC's?  Will it cause protocol thrashing in any way?  

Radia noted it above - it black-holes traffic to the true MAC location.

> As for the Layer 2 "pings" question, you'd be better off just looking
> for traffic sourced by the MAC in question over a couple of second
> period.  Not sure what you would want to do with that, but if you don't
> see anything you can safely clear your forwarding table 

That works only for bidirectional traffic. Silent listeners that move 
always cause problems - and, as I onted, we shouldn't propose to fix 
that issue.

Joe

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