[rbridge] Shared VLAN learning: What is it and why should we care?

[Silvano Gai]

Caitlin,

You say:

> 
> The most recent drafts effectively block that, by only distributing
> endnode discovery information within a VLAN.

Can we agree that:
- FID is a concept internal to the box;
- FID is never present in any frame;
- The VID to FID mapping is internal to each box and potentially
different on different boxes;
- The VID to FID mapping is never propagated in today networks.

If we have agreed the previous, let's consider what triggers learning:
- In bridges the reception of a data frame with a {VID, MAC address}
pair;
- In Rbridges the reception of a per VLAN instance ISIS PDU that
contains a {VID, MAC address} pair.
I don't see any difference.

Both Rbridges and Bridges learn this information as SVL or IVL,
depending on their configuration. It is an internal decision of each
device. It is not something that is or must be propagated among devices.
Again, I don't see any difference.

The only caution is that an RBridge must only include in its ISIS
announcement the {VID, MAC address} pairs that it has learnt observing
traffic, not the ones that derives from its internal mapping of VIDs to
FIDs.

-- Silvano