Users Guide

IP Routing 1197
ARP Table
The router maintains an ARP table that associates a MAC address (Link layer
address) and outgoing port with an IP address and VLAN (Network layer
address). The ARP table is dynamically updated with the station MAC
address and outgoing port information for directly attached subnets. ARP
entries are associated with the VLAN (subnet) on which the IP address or
route is known. The router broadcasts an ARP request in the associated
VLAN for any unknown MAC address to which it needs to route packets. The
router also refreshes an ARP entry by sending an ARP request before a
dynamically learned ARP entry times out and updates the ARP table if a
response is received. Host or VM movement within the same VLAN (Layer-2
topology change) does not trigger an ARP refresh. Only if the ARP entry is
timed out or the port associated with the ARP entry goes down does the ARP
entry get refreshed.
If the traffic to a host is bidirectional, it will result in the host ARP entry
pointing to the new port. Any gratuitous ARP request sent by a host or VM
results in an ARP entry update (including a change in the MAC address and
outgoing port).