From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat May 21 2005 - 08:28:55 GMT-3
Hi Simon,
Off-hand, I'm not sure what the solution is to this mystery is but I suspect
the answer lies somewhere in the root bridge inconsistency you noticed.
Here's my thinking:
R6, which is bridging between the 2 sub-int's doesn't have any concept of
per-vlan STP. But, as Root bridge, it just sends out bpdu's via it's ISL
trunk to the switch.
What happens when the switch gets those bpdu's from R6?
I don't really know. But, I know this. The switch is not using the bdpu's
from R6 to determine which device is the root bridge for vlan 1 and vlan 4.
The switch does have a concept of per-vlan STP and for vlan 1 and vlan 4 and
considers itself the root for both vlan's. This can't be good.
As an experiment, try lowering the bridge priority on the switch for vlan 1
and vlan 4. What happens as a result?
Here's something else to think about. You have an ISL trunk between R6 and
the switch. How are the bpdu's tagged by the router and switch given that
R6 doesn't have a concept of per-vlan STP and the switch does?
Now, having just read your follow-up post, I feel even more strongly that
the treatment of BPDU's is in some way causing this problem since the
problem goes away when you use 802.1q trunk instead of an ISL trunk.
Another possible way to investigate this is by using a debug command on the
switch. I forget exactly which one shows bpdu's but think such a debug
exists.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
simon hart
Sent: Saturday, May 21, 2005 3:39 AM
To: ccielab@groupstudy.com
Subject: Bridging on isl trunks
Hi all,
I am having a problem bridging across two isl trunks on a router. My set up
is like this
13.13.23.1 13.13.23.5
Rtr 1 Rtr 5
| |
vlan 4 vlan 1
\ /
\ /
\ /
\ /
Switch 1
|
|
isl trunk
fa0/0.1 fa0/0.4
vl1 vl4
Rtr6
I am attempting to have Rtr 1 speak to Rtr 5 by bridging on Rtr6. At first
sight I would see this as pretty straightforward, however I a cannot seem to
get it working.
My config on Rtr 6 looks like this
bridge irb
bridge 1 protocol ieee
int fa1/0.1
encaps isl 1
bridge 1
int fa1/0.4
encaps isl 4
bridge 1
My mac table for Bridge 1 on Rtr 6 looks like this
Rack1R6#sh bridge 1
Total of 300 station blocks, 297 free
Codes: P - permanent, S - self
Bridge Group 1:
Address Action Interface Age RX count TX count
0000.0c0a.2804 forward Fa1/0.4 1 1 0
Rtr 1
0003.6b37.c981 forward Fa1/0.1 0 4 0
Rtr 5
000e.381f.d106 forward Fa1/0.1 0 35 0
Int Vlan 1
I can confirm that the mac addresses for each are those that I would expect
from Rtr 1, Rtr 5 and my Interface Vlan 1 on Switch 1.
Now I cannot ping between the two, I get no response. It appears that the
Routers (either 1 or 5) send out an ARP but gets no reply. On each arp the
RX count increases by one on Rtr6, but the Tx Count does not go up. This
leads me to believe that bridge 1 on Rtr 6 is not forwarding the frames
recieved on one vlan to the other
SPANNING TREE
I have noticed that there maybe some inconsisitency with spanning tree. Here
is the output of SPT on Rtr 6 ( I attempted to make R6 the root by using
bridge priority 0)
Bridge group 1
Spanning tree enabled protocol ieee
Root ID Priority 0
Address 0005.9bc5.fad0
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 0
Address 0005.9bc5.fad0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port
ID
-------------------- ------- ---- ----- --- ----- -------------------- -----
-- FastEthernet1/0.1 128.17 128 19 FWD 0 0 0005.9bc5.fad0 128.17 FastEthernet1/0.4 128.18 128 19 FWD 0 0 0005.9bc5.fad0 128.18Here is the output from Switch 1 for both Vlan 4 and Vlan 1
VLAN0004 Spanning tree enabled protocol ieee Root ID Priority 32772 Address 000e.381f.d100 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32772 (priority 32768 sys-id-ext 4) Address 000e.381f.d100 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300
Interface Port ID Designated Port ID Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr ---------------- -------- --------- --- --------- -------------------- ----- --- Fa0/1 128.1 100 FWD 0 32772 000e.381f.d100 128.1 Fa0/6 128.6 19 FWD 0 32772 000e.381f.d100 128.6
VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 000e.381f.d100 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 000e.381f.d100 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15
Interface Port ID Designated Port ID Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr ---------------- -------- --------- --- --------- -------------------- ----- --- Fa0/5 128.5 100 FWD 0 32769 000e.381f.d100 128.5 Fa0/6 128.6 19 FWD 0 32769 000e.381f.d100 128.6
So it seems that both the switch and Rtr 6 think they are the roots for both spanning trees!!
Does anyone have any idea why this should be occurring, or any other useful debug tools that I could use to determine the underlying cause of this problem.
TIA
Simon
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