for whatever reason, my mind has been ensnared with thoughts of the Cat 3920
token ring switch and various implications.
I want to run a couple of concepts through the list, just to check that my
understanding is correct.
So, because of the nature of token ring, one has to do some jiggering to do
token ring switching. IBM or whomever, in their wisdom, came up with the
following model:
in general - token ring bridging works on the ringbridgering model
port - into which plugs some physical token ring device, which may be a
router, an end station, or a token ring shared media device like a mau. (
much the way one might plug ethernet hubs into switch ports ) A port can
connect only to one TrCRF ( see next layer )
TrCRF - token ring concentrator ring function. This is the logical virtual
ring. more than one physical port can connect to a TrCRF, which in turn can
connect to only one TrBRF ( see next layer )
TrBRF - token ring bridge relay function. As implied by the name, the TrBRF
bridges between the virtual rings. The TrBRF is also the "VLAN". therefore
routing must occur between stations ultimately connected through different
TrBRF's.
This is what I am not sure about. Per the 3920 simulator I am using
different BRF's can be on the same subnet. I don't have access to a real
device to see if this is true in the real world.
Also, there is a decent explaination of token ring vlans in the Kennedy
Clark book Cisco Lan Switching. However, Clark seems to emphasize source
route switching, and the advantages in terms of explorers, rather than
straight ( if there is such a thing in token ring ) switching, and the
advantages to end stations.
One of the things I am getting around to in this post is DLSw over a token
ring switch. DLSw is configured on a cisco router using bridging and a
virtual ring which is created across a TCP network between peers.
router ----virtual_ring------router
| |
TR_port TR_port
with the configuration of the TR port using the source-bridge set of
commands source-bridge source-ring-number bridge-number target-ring-number
If I wanted to run DLSw across a 3920, then on my router ( whose token ring
port is plugged into a 3920 ) I would use the source-bridge
source-ring-number bridge-number target-ring-number comand. The source ring
would be identical to the TrCRF ring, the bridge would be the TrBRF, and the
target ring would be the DLSw virtual ring, as confgured under DLSw. Is that
correct?
Sorry if this is a bit disjointed. I'm working from home today and the
family seem to think that if they are on vacation, so am I.
Any thoughts would be appreciated.
Chuck
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