arp

Time interval in minutes between ARP updates. In environments where the number of ARP entries to update is high (for example, on routers only, metro Ethernet environments), increasing the time between updates can improve system performance.

• Range: 1 through 240

Configures the maximum number of retries the device attempts for ARP. The default retry attempts for ARP is 4.

IP address to map to the MAC address. The IP address specified must be part of the subnet defined in the enclosing address statement.

MAC address to map to the IP address. Specify the MAC address as six hexadecimal bytes in one of the following formats: nnnn.nnnn.nnnn or nn:nn:nn:nn:nn:nn. For example, 0000.5e00.5355 or 00:00:5e:00:53:55.

Multicast MAC address to map to the IP address. Specify the multicast MAC address as six hexadecimal bytes in one of the following formats: nnnn.nnnn.nnnn or nn:nn:nn:nn:nn:nn. For example, 0000.5e00.5355 or 00:00:5e:00:53:55.

(Optional) Have the router or switch reply to ARP requests for the specified IP address. If you omit this option, the router or switch uses the entry to reach the destination but does not reply to ARP requests.

Configure a delay for gratuitous ARP requests at the system level. By default, Junos OS sends gratuitous ARP requests immediately after network-related configuration changes are made on an interface (for example, a VLAN ID, MAC address, IP address change, or Aggregated Ethernet deployment). This might lead to the Packet Forwarding Engine dropping some initial request packets if the configuration updates have not been fully processed. To avoid such request packets being dropped, you can configure a delay in gratuitous ARP requests.

• Values:

  • seconds—Configure the ARP request delay in seconds. We recommend configuring a value in the range of 3 through 6 seconds.

Add this statement to the [edit system arp] hierarchy to configure Junos OS to automatically issue a gratuitous ARP announcement when an interface is online.

Specify the ARP aging timer in minutes for a logical interface of family type inet. The ARP aging timer is the time between ARP updates.

• Default: 20

• Range: 1 through 600,000

Configure the device to reply to ARP requests from subscribers only. Do not reply to ARP requests from non-subscribers.

Configure backup VRRP routers or switches to learn the ARP mappings (IP-to-MAC address) for hosts sending the requests. By default, the backup VRRP router drops these requests; therefore, if the primary router fails, the backup router must learn all entries present in the ARP cache of the primary router. Configuring passive learning reduces transition delay when the backup router is activated. Learning of ARP mappings (IP-to-MAC address) by backup VRRP routers or switches for hosts sending the requests is disabled unless this statement is configured.

Purge obsolete ARP entries from the cache when an interface or link goes offline.

Respond to ARP requests from a source that is not directly attached to the local subnet.

Send a unicast ARP request instead of the default broadcast request when an ARP cache entry ages out. When you include this option, the host device sends the requests only to the expected (currently cached) address. The ARP retry requests are unicast at intervals of 5 seconds. When you do not configure the unicast-mode-on-expire option, ARP retries are broadcast at intervals of 800 milliseconds.

This option reduces the amount of broadcast traffic normally sent to resolve expiring addresses. It also supports a special use case where access nodes are configured not to forward broadcast ARP requests towards customer CPEs for security reasons and instead translate ARP broadcasts to unicast requests.