A switch builds or updates this table every time a frame enters a switch interface. A switch will maintain a MAC address table, which relates a particular MAC address to a switch interface. Entries in a host's ARP cache have a timeout, and they will be eventually be flushed if there is no activity for that entry.Ī switch only floods an unknown unicast, and switches don't ask who has a certain MAC address. Hosts populate an ARP cache with layer-3 addresses which have been resolved to layer-2 addresses so that ARP is only used the first time a host wants to send something to another host. ![]() An ARP request is broadcast on layer-2, asking, "Who has this layer-3 address?" The host with that layer-3 address will unicast back to the requesting host with its layer-2 address. ARP (Address Resolution Protocol) is used by a source host to resolve the layer-3 address of a destination host to that host's layer-2 address.
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