Adding a Static ARP Entry
ARP inspection compares ARP packets with static ARP entries in the ARP table. Although hosts identify a packet destination by an IP address, the actual delivery of the packet on Ethernet relies on the Ethernet MAC address. When a router or host wants to deliver a packet on a directly connected network, it sends an ARP request asking for the MAC address associated with the IP address, and then delivers the packet to the MAC address according to the ARP response. The host or router keeps an ARP table so it does not have to send ARP requests for every packet it needs to deliver. The ARP table is dynamically updated whenever ARP responses are sent on the network, and if an entry is not used for a period of time, it times out. If an entry is incorrect (for example, the MAC address changes for a given IP address), the entry times out before it can be updated.
Note The transparent firewall uses dynamic ARP entries in the ARP table for traffic to and from the security appliance, such as management traffic.
To add a static ARP entry, enter the following command:
hostname(config)# arp interface_name ip_address mac_address
For example, to allow ARP responses from the router at 10.1.1.1 with the MAC address 0009.7cbe.2100 on the outside interface, enter the following command:
hostname(config)# arp outside 10.1.1.1 0009.7cbe.2100
Continue reading here: Enabling IPSec over TCP
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