multi parallel pvc's and bridging

From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Apr 09 2005 - 13:17:39 GMT-3


Hi guys,
 
Look at this scenario. There are 2 pvc's going between R-A and R-B. In this
example, they just happen to be ATM, but could just as well been f/r pvc's.
 
 
 
R-A's config:
 
interface ATM3/0
 bandwidth 1544
 no ip address
 no atm ilmi-keepalive
 pvc 100/100
 !
 pvc 200/200
 !
 bridge-group 1
 
 
R-B's config:
 
interface ATM3/0.1 multipoint
 bandwidth 1544
 pvc 100/100
 !
 bridge-group 1
!
interface ATM3/0.2 multipoint
 bandwidth 1544
 pvc 200/200
 !
 bridge-group 1
 
 
 
I've got a couple questions about this config. Maybe someone can help me
understand this better.
 
First, let me confirm that although the config's for R-A and R-B are done a
little differently, functionally they're equivalent, correct?
 
(If that's not true, then my real questions might not make any sense.)
 
OK, here's what I need to understand.
 
Is the above config for R-A and R-B functionally equivalent to having an
etherchannel between R-A and R-B except instead of 2 physical links, there
are 2 logical links?
 
I want to make sure because otherwise there would be spanning tree issues
and one of the pvc's will be blocked.
 
If these 2 pvc's are being treated like an etherchannel, why is that?
 
From looking at these config's, I would have thought that the routers would
treat each pvc like a physical link and then used STP to block one of the
pvc's, but that doesn't seem to be happening. (I did a show span and all
pvc's were forwarding.)
 
If someone can explain this, I'd be very grateful.
 
TIA, Tim



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