[rbridge] Proposal to make VLAN mapping work

[Radia Perlman]

Dinesh, which of the alternative approaches to b) do you prefer, namely:

1) If RB1 notices X maps to Y, RB1 reports "X maps to Y" in its Hello,
and there must only be one forwarder for the set {X,Y}, but all the 
other VLANs
can be divvied out to lots of other forwarders

2) If RB1 notices that any VLAN maps to any other VLAN, it simply
sets a flag in its Hello saying "VLAN mapping is occurring on this cloud",
and there must be only one appointed forwarder for all VLANs on that link.

I personally prefer 2). I would have preferred only the DRB forward to/from
the link (simpler, safer) in all cases, but certainly if we say that 
there can
only be a single forwarder in the (hopefully rare) case where VLANs are
being mapped within the link, that seems like not a big restriction.

If we do 2), that means a whole lot information to encode in a Hello. Just
a flag "I've detected VLAN mapping". The alternative (1) requires encoding
which VLANs map to which other VLANs.

Radia




Dinesh G Dutt wrote:
> Radia Perlman wrote:
>   
>> I think I understand what Caitlin is saying, and let me say it in 
>> different words.
>> What Caitlin is saying: Avoid VLAN mapping entirely by just
>> renumbering the VLAN that needs to change.
>>     
> I understood the same. That's unfortunately not always the choice,
>   
>> So I think our options are:
>> a) explicitly not support VLAN mapping. Declare it a misconfiguration 
>> if it is detected, and
>> make the network owner renumber things so no VLAN mapping is 
>> occurring. (this is
>> how the current spec reads)
>> b) allow for support by changing the spec to include information in 
>> IS-IS Hellos
>> to alert the DRB that VLAN mapping is going on.
>>
>> So, anyway...I recommend we do "b", namely alert the DRB that VLAN
>> mapping is going on, and have the DRB make sure there is only one
>> forwarder for any mapped VLANs, and don't say anything else in the
>> spec about VLAN mapping. That way there are sufficient hooks so
>> that someone can implement VLAN mapping if they want.
>>     
> That is fine by me. That is why I believe you suggested documenting the 
> other changes in a separate draft.
>
> Dinesh
>
>