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Unicast flooding

Hi all


Within our network we are seeing unicast flooding for 3 of our devices.


based on the topology attached the SNMP server sends a get request to the UPS which has to be routed to VLAN 20. when I run wireshark on my pc in VLAN 20 I am seeing all of the unicast traffic destined for the UPS.  When I look at the CAM table on the multilayer switch I can see that it has no entry for the MAc address of the UPS but I would expect it to learn it after the intital snmp request.  there are other devices within VLAN 20 also being polled and these are all being learned fine its just this UPS and a couple of other devices.


the SNMP server is running on centos


Any suggestions?





Super Bronze

Can you ping the UPS from

Can you ping the UPS from your L3 switch?  If so, CAM still empty?

I cant ping the device from

I cant ping the device from the L3 swicth i get timeouts but it does add the device to the cam table but then after 5 minutes its removed again even though there is SNMP traffic passing through the switch every minute.

Super Bronze

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I would investigate why the host doesn't respond to pings.

If the L3 switch doesn't see enough frames from the host, it will time out its CAM and new frames sent to that host will flood.

when I ssh onto the core via

when I ssh onto the core via (the SVI) and try to ping what process does the switch take as its also acting as the default gateway out for VLAN 10? and I wanna ping so I need to send this to my default gateway... hang on a minute I am the default gateway ok... ill lookup my routing table and see if I have a route for the network which ill do so ill pass it to


Does the above process work or does the core trip up when it tries to send it to itself? hope that make sense! :P


Edit: Putting a ststic MAC entry into the cores CAM table resolves the unicast flooding but still doesnt explain why its not learning the MAC address.

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