arp
Syntax
arp ip-address (mac | multicast-mac) mac-address publish;
arp {
aging-timer minutes;
gratuitous-arp-delayseconds;
gratuitous-arp-on-ifup;
interfaces {
interface-name {
aging-timer minutes;
}
}
non-subscriber-no-reply;
passive-learning;
purging;
unicast-mode-on-expire;
}
Syntax (EX Series)
arp {
aging-timer minutes;
}
Hierarchy Level
[edit interfaces interface-name unit logical-unit-number family inet address address]
[edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number family inet address address]
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.
NoteBy 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.
NoteFor EX-Series switches, set only the time interval between
ARP updates.
Options
ip-address—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 mac-address—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 mac-address—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.
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.
NoteFor unicast MAC addresses only, if you include the publish option, the router or switch replies to proxy ARP requests.
aging-timer—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.
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.
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.
Range: 1 through 6,00,000
non-subscriber-no-reply—Configure 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-expire—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.
NoteThis 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.
