cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Announcements
Join Customer Connection to register!
777
Views
0
Helpful
1
Replies
Vincenzo Santoro
Beginner

STP state sync events - Multicast flooding

Hi all,

Debugging the STP state sync events on a Cisco 3560 running 12.2(55)SE1 through the following command:

debug spanning-tree synchronization

Every 2 minutes I get the following messages:

May  6 10:13:14: STP sync:  Send ALL port data to all other switches...
May  6 10:13:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:15:14: STP sync:  Send ALL port data to all other switches...
May  6 10:15:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:17:14: STP sync:  Send ALL port data to all other switches...
May  6 10:17:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:19:14: STP sync:  Send ALL port data to all other switches...
May  6 10:19:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:21:14: STP sync:  Send ALL port data to all other switches...
May  6 10:21:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:23:14: STP sync:  Send ALL port data to all other switches...
May  6 10:23:14: STP sync:  NULL sync_data -- nothing to send
May  6 10:25:14: STP sync:  Send ALL port data to all other switches...
May  6 10:25:14: STP sync:  NULL sync_data -- nothing to send

Could anyone explain what does  "Send ALL port data to all other switches..." mean?  Can I disable the STP synchronization protocol?

As I'm running IGMP snooping on that switch, every time I receive the messages above, these are interpretated as a TCN spanning-tree event and the multicast traffic is flooded to all the ports. In order to avoid that, I had to disable the multicast flooding on the uplink interface:

no ip igmp snooping tcn flood

Is it a common procedure or just a bug?

Thanks and regards,

Vincenzo

1 REPLY 1
Giuseppe Larosa
Hall of Fame Master

Hello Vincenzo,

this looks like a bug in 802.1W synchronization is performed when there is a topology change as a wave of STP handshakes

every 2 minutes is too regular to be true

>> "Send ALL port data to all other switches..." mean?

do RSTP handshake sending port role and state to each switch neighbor

to reduce sync activity you should configure edge ports where no switch is expected with spanning-tree portfast but that's all

Hope to help

Giuseppe