[c-nsp] 2960 not switching packets (hub-like behavior)

[Brian Turnbow]

 Most times this is related to the arp aging time on the sending device vs mac aging time on the switch.
 The switch will learn the location of the mac when it transmits, but after not recieving data sourced from the mac for more than the aging time the mac gets removed from the mac addres  table . 
The sending device still has the arp entry so it will still send packets to the destination mac and the switch will start flooding the packets.
Check to see if the destination mac is in your mac table on the switch and the arp table on the originating device. Then try and reconfigure the arp timeoutes lower than the mac aging time by lowering one or raising the other.

Regards
Brian



-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Neils Christoffersen
Sent: giovedì 17 gennaio 2008 17.10
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] 2960 not switching packets (hub-like behavior)

I have a WS-C2960-48TT-L running c2960-lanbasek9-mz.122-25.SEE4

Sniffing traffic on a connected workstation, I can see unicast traffic
destined for other systems connected to the switch. I know this isn't normal
behavior but I have been unable to diagnose the problem. Reloading did not
resolve it.

This is a very simple configuration (single switch behind a firewall, no
vlans) and the network is not highly utilized.

Suggestions?


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