Asymmetric routing & unknown unicasts flooding

[ovt]

Hi!

It is well known that asymmetric routing can cause increase in unknown unicasts flooding. In this case making ARP timeout roughly equal to MAC-aging-time on L3 switch can solve the problem. But which of two timeouts should be changed? What does Cisco recommend?

Oleg Tipisov,

REDCENTER,

Moscow

[umedryk]

Hi,

Adjust the MAC aging time on the respective switches to 14,400 seconds (four hours).

Change the ARP timeout on the routers to five minutes (300 seconds).

Changing the MAC aging time and ARP timeout to the same timeout value.

The preferable method is to change the MAC aging time to 14,400 seconds.