Help with 2 mac-address-table commands

Unanswered Question
Oct 5th, 2009

We're having some unicast flooding issues on our network and was told to implement these 2 commands to help with the issue:

mac-address-table synchronize

mac-address-table aging-time 0 routed-mac

Previously we had the aging-time set to 14400 so there is some concern with disable the aging-time using the 2nd command above. What would be the implications of disabling mac-address-table aging? What exactly does mac-address-table synch do?

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Giuseppe Larosa Mon, 10/05/2009 - 11:37

Hello Jshweng,


from command reference 12.2SX

mac-address-table synchronize

To synchronize the Layer 2 MAC address table entries across the Policy Feature Card (PFC) and all the Distributed Forwarding Cards (DFCs), use the mac-address-table synchronize command in global configuration mode. To disable MAC address table synchronization or reset the activity timer, use the no form of this command.

mac-address-table synchronize [activity-time seconds]

no mac-address-table synchronize [activity-time seconds]


less clear

(Optional) Specifies the routed MAC aging interval.

for me you are disabling aging time only for MAC addresses that are classified as routed MAC addresses

Now, the question becomes what these routed MAC addresses are.

Hope to help


nsn-amagruder Mon, 10/05/2009 - 11:52

I'd isolate what is causing the unicast flooding before implementing a solution. Do you have any Windows NLB running? Have you traced down the source/destination mac addresses?


NonStop Networks, LLC

jschweng Mon, 10/05/2009 - 12:00

Good info guys. Most of our unicast flooding is the result of dual-attached servers running Linux with bonding software for the NICs and asymmetric routing in our network as well as a fully meshed switched topology.

Won't setting the aging-timer to 0 mean that the routed MAC entries will never expire and so we may someday run into a situation of exhausting our ARP tables?


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