Category: ARP

ARP timeout resolution is implemented in minutes

Under some circumstances, you might want to tune the ARP timers on the router (for example, when using ARP as a keepalive mechanism to detect whether the host is up). Unfortunately, although you can set the per-interface arp timeout in seconds, the actual timer resolution is in minutes. For example, if you set the ARP timeout to 10 seconds, the router will age the ARP entries once per minute.
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ARP entries are periodically refreshed if you use CEF switching

In a previous post I've been writing about the inability to clean the ARP cache due to cached CEF adjacencies. As it turns out, this behavior has another side effect: the router will automatically refresh all ARP entries (and CEF adjacencies) as they expire from the ARP cache. This might become a problem on high-end devices with a lot of directly connected hosts if you set the arp timeout to a low value.

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