The BIG-IP system is a multi-layer network device, and as such, needs to perform routing functions. To do this, the BIG-IP system must be able to find destination MAC addresses on the network, based on known IP addresses. The way that the BIG-IP system does this is by supporting Address Resolution Protocol (ARP), an industry-standard Layer 3 protocol.
When you use the BIG-IP Configuration utility to view the entries in the ARP cache, you can view the state of each entry:
The system does not respond to ARP requests sent from any firewall that uses a multicast IP address as its source address.
When dynamically updating the ARP cache, the BIG-IP system includes not only entries resulting from responses to ARP requests, but also entries resulting from gratuitous ARP messages.
For security reasons, the system does not fully trust gratuitous ARP entries. Consequently, if there is no existing entry in the cache for the IP address/MAC pair, and the BIG-IP system cannot verify the validity of the gratuitous ARP entry within a short period of time, the BIG-IP system deletes the entry.
You can manage static entries in the ARP cache in various ways.
You can manage dynamic entries in the ARP cache in various ways.
Perform this task to apply global options to all dynamic ARP entries.
|Enabled||Creates an entry in the ARP cache whenever the system receives who-has packets from another host on the network. When you enable this option, you slightly enhance system performance by eliminating the need for the BIG-IP system to perform an additional ARP exchange later.|
|Disabled||Prevents a malicious action known as ARP poisoning. ARP poisoning occurs when a host is intentionally altered to send an ARP response containing a false MAC address.|
You can configure a set of global options for controlling dynamic ARP cache entries.
|Dynamic Timeout||Specifies the maximum number of seconds that a dynamic entry can remain in the ARP cache before the BIG-IP system automatically removes it.|
|Maximum Dynamic Entries||Limits the number of dynamic entries that the BIG-IP system can hold in the ARP cache at any given time. This setting has no effect on the number of static entries that the ARP cache can hold.|
|Request Retries||Specifies the number of times that the BIG-IP system resends an ARP request before finally marking the host as unreachable.|
|Reciprocal Update||Enables the BIG-IP system to store additional information, which is information that the system learns as a result of other hosts on the network sending ARP broadcast requests to the BIG-IP system.|