Re: [trill] Thoughts on active-active edge

[Radia Perlman <[e-mail]>]

I think it would be good to have a document that explains the problem...I
certainly don't believe I know all the cases that need to be solved.  I
think I understand the hypervisor case...where the hypervisor decides which
uplink to send things to, and never forwards between the up-links.

This case is scary because the RBridges on the uplink cannot see Hellos
from each other, so if misconfigured, at the very least I could imagine
multiple RBridges decapsulating multicast from the campus to the hypervisor.

Anyway...how many uplinks do we need to support?  Do we care about problems
due to misconfiguration?

In cases like this, is it common to also have pt-to-pt links between all
the RBs attaching to the hypervisor?  If so, then it seems like it would be
possible for them to coordinate to at least detect misconfiguration, and
possibly play games with forwarding messages to each other (e.g., if one of
them is not attached to a tree and needs to encapsulate a multidestination
frame).

How many trees does the campus need?

Are there cases where there are lots of hypervisors, where they attach to
different subsets of edge RBs?  In that case, we might eat up a lot of
nicknames, since if one hypervisor is attached to {R1, R2}, and another is
attached to {R1, R2, R3}, they cannot use the same pseudonode nickname.

Are there cases other than hypervisors?  I think there are cases of bridges
that have this behavior (a port with a bunch of endnodes, and several
up-links, where the bridge does not forward between the up-links.

If this has been written down anywhere, can anyone point me to it?  If not,
it seems really prudent to answer these (and I'm sure other) questions
before arguing about specific solutions.

Radia