STP issue

[Randy2]

Hi all,

we had a loop problem on our network on a switch connected to the port 24 of the switch i'm showing you the log below :

Apr 20 00:30:09 172.16.22.1 mgr:  SME TELNET from 172.16.7.43 - MANAGER Mode
Apr 20 19:51:12 172.16.22.1 ports:  port 24 is Blocked by STP
Apr 20 19:51:19 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:51:19 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:51:19 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:51:19 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:51:19 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:51:19 172.16.22.1 stp:  CST Root changed from 32768:002347-ac3180 to 32768:0004ea-8dd5c0
Apr 20 19:51:19 172.16.22.1 stp:  IST Root changed from 32768:002347-ac3180 to 32768:84802d-280000
Apr 20 19:51:19 172.16.22.1 stp:  MSTI 1 Root changed from 32768:002347-ac3180 to 4096:0008e3-fffc28
Apr 20 19:51:26 172.16.22.1 FFI:  port 24-Excessive Broadcasts. See help.
Apr 20 19:52:01 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:52:01 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:52:01 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:52:01 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:52:01 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:52:21 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:52:21 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:52:21 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:52:21 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:52:21 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:52:49 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:53:23 172.16.22.1 stp:  MSTI 1 Root changed from 32768:002347-ac3180 to 4096:0008e3-fffc28
Apr 20 19:54:45 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:54:45 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:54:45 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:54:45 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:54:45 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:55:27 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:55:27 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:55:27 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:55:27 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:55:27 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:55:58 172.16.22.1 stp:  MSTI 1 Root changed from 32768:002347-ac3180 to 4096:0008e3-fffc28
Apr 20 19:56:04 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:56:04 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:56:04 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:56:04 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:56:04 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:57:50 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:57:50 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:57:50 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:57:50 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:57:50 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 19:58:28 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 19:58:28 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 19:58:28 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 19:58:28 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 19:58:28 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:00:06 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:00:06 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:00:06 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:00:06 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:00:06 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:00:38 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:00:38 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:00:38 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:00:38 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:00:38 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:01:02 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:01:02 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:01:02 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:01:02 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:01:02 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:01:53 172.16.22.1 ports:  port 20 is now off-line
Apr 20 20:02:07 172.16.22.1 ports:  port 20 is Blocked by STP
Apr 20 20:02:10 172.16.22.1 ports:  port 20 is now on-line
Apr 20 20:02:12 172.16.22.1 ports:  port 20 is now off-line
Apr 20 20:02:14 172.16.22.1 ports:  port 20 is Blocked by STP
Apr 20 20:02:17 172.16.22.1 ports:  port 20 is now on-line
Apr 20 20:02:18 172.16.22.1 FFI:  port 20-Excessive Broadcasts. See help.
Apr 20 20:02:24 172.16.22.1 igmp:  DEFAULT_VLAN: This switch was not elected as Querier
Apr 20 20:02:41 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:02:41 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:02:41 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:02:41 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:02:41 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:02:43 172.16.22.1 stp:  CST Root changed from 32768:002347-ac3180 to 32768:0004ea-8dd5c0
Apr 20 20:02:43 172.16.22.1 stp:  IST Root changed from 32768:002347-ac3180 to 32768:84802d-280000
Apr 20 20:02:43 172.16.22.1 stp:  MSTI 1 Root changed from 32768:002347-ac3180 to 4096:0008e3-fffc28
Apr 20 20:03:00 172.16.22.1 FFI:  port 24-Excessive Broadcasts. See help.
Apr 20 20:03:05 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:03:05 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:03:05 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:03:05 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:03:05 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:03:33 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:03:33 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:03:33 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:03:33 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:03:33 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:03:33 172.16.22.1 stp:  CST Root changed from 32768:002347-ac3180 to 32768:0004ea-8dd5c0
Apr 20 20:03:33 172.16.22.1 stp:  IST Root changed from 32768:002347-ac3180 to 32768:84802d-280000
Apr 20 20:03:33 172.16.22.1 stp:  MSTI 1 Root changed from 32768:002347-ac3180 to 4096:0008e3-fffc28
Apr 20 20:05:27 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:05:27 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:05:27 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:05:27 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:05:27 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:06:11 172.16.22.1 stp:  CIST starved for a BPDU Rx on port 28 from 32768:0008e3-fffc28
Apr 20 20:06:11 172.16.22.1 stp:  CST Root changed from 32768:0004ea-8dd5c0 to 32768:002347-ac3180
Apr 20 20:06:11 172.16.22.1 stp:  IST Root changed from 32768:84802d-280000 to 32768:002347-ac3180
Apr 20 20:06:11 172.16.22.1 stp:  MSTI 1 starved for an MSTI Msg Rx on port 28 from 4096:0008e3-fffc28
Apr 20 20:06:11 172.16.22.1 stp:  MSTI 1 Root changed from 4096:0008e3-fffc28 to 32768:002347-ac3180
Apr 20 20:06:33 172.16.22.1 ports:  port 24 is now on-line
Apr 20 20:06:46 172.16.22.1 ports:  port 24 is Blocked by STP

what i don't understand is how a port that has been blocked by the spanning-tree :

Apr 20 19:51:12 172.16.22.1 ports:  port 24 is Blocked by STP

can still generate excessive broadcast :

Apr 20 19:51:26 172.16.22.1 FFI:  port 24-Excessive Broadcasts. See help.

if it's blocked then no traffic except BPDU should pass ...or maybe i'm missing something or misunderstanding my logs...

i thought that i would have seen a "port 24 is now on-line" if its STP state would have changed

Thanks in advance for your replies

[Vince-Whirlwind · Accepted solution]

Being in spanning-tree blocking mode doesn't stop the switchport from receiving broadcasts, even if it is just dropping them.

If the percentage of the traffic it receives is made up of broadcast frames in excess of a certain percentage, it will give you the "excessive broadcasts" message. 
So this could be a small amount of broadcasts, but no other traffic, making it a high percentage, for example.

I've usually found "excessive broadcasts" can be ignored - if a port is in "blocking" mode, then the mac-address-table won't be pointing any traffic to it, so it will see only broadcast traffic, thus generating the message.

[Randy2]

Thanks for the reply Vince, it makes total sense now you've said it