Uncast flooding on collapsed distribution and core.

[Mark Williams]

In an environment where there is a dedicated router connected to dedicated distribution switches, I understand the need to configure the MAC AGING and ARP timers on each device.

However, in an environment where the distribution switch and router are collapsed (Eg a 3750), does this still need to be done? Will not the ARP table and MAC table always be in sync?

[Joseph W. Doherty]

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Posting

It depends on whether your using a 3750 as a single L3 device or a separate L3 devices.  If you're running a collapsed core with multiple devices, such that ingress and egress paths can differ, unicast flooding can still arise if MAC aging and ARP timers aren't sync'ed.