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Webcast-Catalyst9k
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Spanning-tree unicast flooding and overloaded port

                   I have a solution that has been in production for many years, it is a point-to-point unchannelized DS3 across Adtran Ethernet bridges.

The port has become overloaded and I am seeing a recalculation of spanning-tree.


The two devices are 6509-E and 3560. See attach for drawing.

I was wondering if a max-age timer could be adjusted to help correct this ?

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Spanning-tree unicast flooding and overloaded port

The default of the max age timer is 20 seconds, in other words 10 hellos - common tuning (if at all) is to lessen it.

If you want to change it you'll have to do it on a vlan basis which will affect the whole LAN I guess.

Plus I think adjusting the timers won't solve the problem in this case.

Seeing your topology I wonder if there is any chance of the occurrence of a loop between the 6509 and the 3560?

If not you could filter the BPDUs.

If that's to risky I'd make sure that the BPDUs are transmitted even when the DS3 link is experiencing congestinon.

The problem is that the switchports will not recoginze the congestion, have you considered policing the switchports to DS3 speed?

BTW: What STP version are you running?

Hope that helps

Rolf

1 REPLY

Spanning-tree unicast flooding and overloaded port

The default of the max age timer is 20 seconds, in other words 10 hellos - common tuning (if at all) is to lessen it.

If you want to change it you'll have to do it on a vlan basis which will affect the whole LAN I guess.

Plus I think adjusting the timers won't solve the problem in this case.

Seeing your topology I wonder if there is any chance of the occurrence of a loop between the 6509 and the 3560?

If not you could filter the BPDUs.

If that's to risky I'd make sure that the BPDUs are transmitted even when the DS3 link is experiencing congestinon.

The problem is that the switchports will not recoginze the congestion, have you considered policing the switchports to DS3 speed?

BTW: What STP version are you running?

Hope that helps

Rolf

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