Port blocked by STP let 1 VLAN passed ...

[Cisco SOGET]

Hello

I have a problem with a stack 3750. A port blocked by STP let traffic passed for a VLAN (only one !).

If simebody have an idea ...

Laurent Malandain

[Amit Singh]

The issue what you are seeing might be unicast flooding on the switch.

 
You can read up on unicast flooding caused by assymetric routing here:
Asymmetric Routing and HSRP (Excessive Flooding of Unicast Traffic in Network with Routers That Run HSRP)
http://www.cisco.com/en/US/customer/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml#t8
 
To combat this issue, you will need to configure the ARP timeout value less than the CAM aging time.
 
eg. 
Router(config)#int vlan 2
Router(config-if)#arp timeout 240 

HTH,
Cheers,
-amit singh