[rbridge] Proposal to make VLAN mapping work

[Dinesh G Dutt]

Hi Caitlin,

I don't think doing everything at the edge works. Consider a ARP request 
originating in the East Cloud in VLAN X. It must hit all end stations in 
VLAN X in the East Cloud and all end stations in VLAN Y in the West 
Cloud (assuming X is mapped to Y going from E->W). If I don't change the 
VLAN mapping at the RBridge connecting the two clouds, then it'll reach 
the wrong set of stations in the total cloud.

Was that clear ?

It's not that each core needs to do its own VLAN pruning. Consider a 
simple 3 switch network where VLAN 1 is mapped to VLAN 4 going from E->W 
and VLAN 1 is mapped to VLAN 3 going from W->E. R2 is doing the mapping 
(though in this trivial case, the edge mapping works fine, but add 
another switch to either side of R2 and edge mapping doesn't work).

                                        R1 -- R2 -- R3

Since there are no endstations in VLAN 1, VLAN 3 or VLAN 4 connected to 
R2, if R2 doesn't express an interest in at least VLAN 1, neither R1 nor 
R3 will send it any multi-destination VLAN 1 frames and R2 can therefore 
not really propagate the frames from one side to another.

Dinesh
Caitlin Bestler wrote:
>   
>> -----Original Message-----
>> From: Dinesh G Dutt [mailto:ddutt at cisco.com]
>> Sent: Wednesday, September 17, 2008 8:19 AM
>> To: Caitlin Bestler
>> Cc: Radia Perlman; rbridge at postel.org
>> Subject: Re: [rbridge] Proposal to make VLAN mapping work
>>
>> Caitlin,
>>
>> I was of the same opinion, until I realized that VLAN pruning in the
>> broadcast trees and multicast pruning requires us to modify the
>>     
> control
>   
>> protocol, especially since the Rbridges that are doing the mapping are
>> sort of in the core of the network when the networks are merging.
>>
>> Dinesh
>>     
>
> Dinesh,
>
> Are you saying that in the "merged network" scenario, that there would
> essentially be an "East Core" and a "West Core", and that each needs
> to do its own VLAN pruning separate  from the East/West VLAN Mapping
> Bridges are considered?
>
> That would be a justification for the more complex solution.
>
> But just to kick the tires one more time, why can't the end stations
> and bridges operating with legacy non-integrated VLAN Maps be
> partitioned at the edges?
>
>
>   

-- 
We make our world significant by the courage of our questions and by 
the depth of our answers.                               - Carl Sagan