[rbridge] Avoiding sending multiple IS-IS Hellos tagged with allthe VLAN tags

[Dinesh G Dutt]

Radia Perlman wrote:
> I'd like to understand what problem customers are attempting to solve with
> partitioned VLANs, and what hardship it would present to require at 
> least one of the
>   
The primary problem with having a VLAN everywhere is that the root of 
the spanning tree moves around leading to non-optimal forwarding in 
enterprise networks. Enterprise networks are carefully engineered 
networks and in the event of failure, they want to localize the effects 
as much as possible. So, they want each VLAN to be localized and roots 
where they want it to be. Having a common VLAN messes up that 
arrangement. Also, VLAN 1 is the default VLAN when a switch comes up and 
there is typically lots of customer data on it.
> VLANs to *not* be partitioned. With TRILL, if a customer eventually replaces
> all bridges, the customer will not be able to partition VLANs anymore. 
>   
As I raised it in the meeting, this is a side-effect that has not been 
considered before and needs to be carefully thought through. I don't 
think many people are aware of this issue with TRILL that doesn't exist 
with 802.1Q bridges today.
> Also, from
> what Anoop was explaining to me, the GVRP protocol would automatically
> configure the switch-to-switch links to join all the islands of VLANs. 
> So it would
> seem as though it can't be that fatal to solving customer problems to 
> require
> *one* VLAN on a layer 2 cloud to not be partitioned.
>   
GVRP is not deployed by a significant majority of customers.

Dinesh

-- 
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the depth of our answers.                               - Carl Sagan