[rbridge] Proposal to make VLAN mapping work
Dinesh G Dutt
ddutt at cisco.com
Wed Sep 17 10:28:08 PDT 2008
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.
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
>> I was of the same opinion, until I realized that VLAN pruning in the
>> broadcast trees and multicast pruning requires us to modify the
>> protocol, especially since the Rbridges that are doing the mapping are
>> sort of in the core of the network when the networks are merging.
> 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
More information about the rbridge