When a router receives a packet with unknown destination MAC (perhaps due to arp time out), how does the router respond? Will it broadcast the packet or broadcast an arp request instead? I find it a little confusing when I see these two solutions in different articles. Thanks.
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ARP (Address Resolution Protocol) is used to convert an IP address into a MAC address. If the router has an unknown MAC address, ARP won't fix it.
It could try RARP (Reverse ARP), but it's easier to simply broadcast it. That's exactly what an unmanaged switch does, until it 'learns' where a MAC address is by receiving it as a source address.
More sophisticated routers can be configured to do a number of things - including dropping the frame.
John Burger
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As far as I know, the router sends out an ARP request if said MAC address is not on the ARP table. If no one answers, it gets dropped.
Aloha
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