Just need your assistance in understanding BackBone fast feature...
I have a simple topology as below:
My understanding is, with backbone fast enabled, when the port Gig0/3 on SW2 receives a inferior BPDU it skips the Max-age then starts its transition towards Forwarding.
According to cisco documentation http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800c2548.shtml
Inferior BPDU is defined by:
If an inferior BPDU is received on a port from our designated bridge, then this bridge has:
- Lost the root and starts to advertise a root with a higher bridge ID, a worse root than ours.
- Or its path to the root has increased above ours.
I tried case 1, it was working perfectly fine. The problem is with Case 2:
SW3 is a designated bridge and when I increase its cost to the Root (link b/w Sw3 - Sw1) then I would expect the following changes.
1. Gig0/2 is the new Root port for SW3
2. Fa0/31 on Sw3 will be blocked.
3. Gig0/3 on SW2 will be forwarding.
All the three are happing but in this case, since the gig0/3 on SW2 now receiving an inferior BPDU I would expect it to send RLQ Msg's but I dont see that ..
The transitions are happening but no RLQ msg's sent..
*Mar 1 20:27:58.786: STP: VLAN0001 Gi0/3 -> listening
*Mar 1 20:27:59.834: STP: VLAN0001 Topology Change rcvd on Gi0/3
*Mar 1 20:27:59.834: STP: VLAN0001 sent Topology Change Notice on Fa0/47
*Mar 1 20:28:13.793: STP: VLAN0001 Gi0/3 -> learning
*Mar 1 20:28:28.800: STP: Generating TC trap for port GigabitEthernet0/3
*Mar 1 20:28:28.800: STP: VLAN0001 sent Topology Change Notice on Fa0/47
*Mar 1 20:28:28.800: STP: VLAN0001 Gi0/3 -> forwarding
Am I missing something here? or have I totally misunderstood the concept?