From: ggombas@gmail.com
Date: Sun Apr 15 2007 - 13:22:09 ART
Hello groupstudy,
I was hoping to clear up some misconceptions regarding the spanning tree portfast and bpdufilter feature on Cisco switches.
In some Cisco texts and even on this group I have read that a port configured with portfast and bpdufilter "loses its Port Fast-operational status, and BPDU filtering is disabled" when it hears a BPDU.
In reality I have seen the opposite. In the example below I configured a Cat 3560 swithport with portfast and bpdufilter and connected it to another switch configured as the root.
As you can see the port is still in portfast mode and bpdufilter is still enabled:
SW1#show spanning-tree int fa0/1 det
Port 3 (FastEthernet0/1) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.3.
Designated root has priority 24577, address 000b.4635.8780
Designated bridge has priority 32769, address 000a.b80a.df00
Designated port id is 128.3, designated path cost 19
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
The port is in the portfast mode
Link type is point-to-point by default
Bpdu filter is enabled
BPDU: sent 0, received 0
This makes sense because bpdufilter is preventing the port from ever seeing the bpdu's. This is actually preventing the port from being removed from portfast mode.
Once I remove the bpdufilter then the port is taken out of portfast mode:
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#int fa0/1
SW1(config-if)#no spanning-tree bpdufilter
SW1#show spanning-tree int fa0/1 det
Port 3 (FastEthernet0/1) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.3.
Designated root has priority 4096, address 0050.0f01.1901
Designated bridge has priority 4096, address 0050.0f01.1901
Designated port id is 128.6, designated path cost 0
Timers: message age 1, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 1, received 6
By the way - the default behavior of a switch is to remove a port from portfast mode when it hears a BPDU on that port (whether bpdufilter is configured or not).
Please tell me if my observations are correct or if I am seeing a bug.
Thanks,
Greg
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