Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 

arp

 

Syntax

Syntax (EX Series)

Hierarchy Level

Note

The edit logical-systems hierarchy is not available on QFabric systems.

Release Information

Statement introduced before Junos OS Release 7.4.

Statement introduced in Junos OS Release 9.0 for EX Series switches.

Statement introduced in Junos OS Release 11.1 for the QFX Series.

Statement introduced in Junos OS Release 14.1X53-D20 for the OCX Series.

Description

For Ethernet, Fast Ethernet, and Gigabit Ethernet interfaces only, configure Address Resolution Protocol (ARP) table entries mapping IP addresses to MAC addresses. IPv4 networks use ARP to map IP network addresses to physical (MAC) addresses. An address is resolved when the host device receives a proper ARP reply in response to the ARP request that it sent to a broadcast Ethernet address. The resolved addresses are stored in the ARP table for a configurable period of time. When an entry is close to expiration, it triggers the host to broadcast another ARP request to update the entry for that address. Only the intended receiver responds to the broadcast request; other recipients silently drop the request packet.

You can enable backup VRRP routers to learn ARP requests for VRRP-IP to VRRP-MAC address translation. You can also set the time interval between ARP updates.

Note

By default, an ARP policer is installed that is shared among all the Ethernet interfaces on which you have configured the family inet statement. By including the arp statement at the [edit interfaces interface-name unit logical-unit-number family inet policer] hierarchy level, you can apply a specific ARP-packet policer to an interface. This feature is not available on EX Series switches.

When you need to conserve IP addresses, you can configure an Ethernet interface to be unnumbered by including the unnumbered-address statement at the [edit interfaces interface-name unit logical-unit-number family inet] hierarchy level.

Note

For EX-Series switches, set only the time interval between ARP updates.

Options

ip-addressIP address to map to the MAC address. The IP address specified must be part of the subnet defined in the enclosing address statement.
mac mac-addressMAC 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 mac-addressMulticast 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.
publish(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.
Note

For unicast MAC addresses only, if you include the publish option, the router or switch replies to proxy ARP requests.

aging-timerTime 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.
gratuitous-arp-delay 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.

gratuitous-arp-on-ifup 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.
interfaces Specify the ARP aging timer in minutes for a logical interface of family type inet.

Values: aging-timer minutes—Time between ARP updates, in minutes.

Default: 20

Range: 1 through 6,00,000

non-subscriber-no-replyConfigure the device to reply to ARP requests from subscribers only. Do not reply to ARP requests from non-subscribers.
passive-learning 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.
purging Purge obsolete ARP entries from the cache when an interface or link goes offline.
unicast-mode-on-expireSend 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.

Note

This option affects only the update requests. Initial ARP requests are broadcast as usual.

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.

system—To view this statement in the configuration.

system-control—To add this statement to the configuration.