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Why there is Potential Loops in Transparent Mode failover?

I can't understand. Suppose both FWSM is active,both fwsm will transfer packet from inside to outside. But inside vlan and outside vlan is different vlan. So how it will make Potential Loops ?

I think if I permit bpdu on inside and outside, it will make Potential Loops.

For example,vlan 400 is inside vlan and vlan 255 is outside vlan. If I permit bpdu on inside and outside interface. There is same STP root for those two vlan.

6509-B#sh spanning-tree vlan 400

VLAN0400

Spanning tree enabled protocol ieee

Root ID Priority 32768

Address 000a.f357.f37f

Cost 3

Port 1665 (Port-channel1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768

Address 0012.440f.3090

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Po1 Root FWD 3 128.1665 P2p

Po272 Desg FWD 3 128.1666 Edge P2p

6509-B#sh spanning-tree vlan 255

VLAN0255

Spanning tree enabled protocol ieee

Root ID Priority 32768

Address 000a.f357.f37f

Cost 3

Port 1665 (Port-channel1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768

Address 0012.440f.2fff

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Po1 Root FWD 3 128.1665 P2p

Po272 Desg FWD 3 128.1666 Edge P2p

any comments are appreciated!

thanks!

1 REPLY
Silver

Re: Why there is Potential Loops in Transparent Mode failover?

To avoid loops when you use failover in transparent mode, you must use switch software that supports BPDU forwarding, and you must configure the FWSM to allow BPDUs. See the "Chassis System Requirements" section for switch software versions that allow BPDUs automatically.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/mod_icn/fwsm/fwsm_2_2/fwsm_cfg/failover.htm

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