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This chapter describes the commands used to configure and monitor the Address Resolution Protocol (ARP ).
For detailed information about ARP concepts, configuration tasks, and examples, refer to the Cisco IOS XR IP Addresses and Services Configuration Guide for the Cisco XR 12000 Series Router.
To add a permanent entry in the Address Resolution Protocol (ARP) cache, use the arp command in Global Configuration mode. To remove an entry from the ARP cache, enter the no form of this command.
arp [ vrf vrf-name ] ip-address hardware-address encapsulation-type [alias]
no arp [ vrf vrf-name ] ip-address hardware-address encapsulation-type [alias]
vrf |
(Optional) Specifies VPN routing and forwarding (VRF) instance. |
vrf-name |
(Optional) VRF instance that identifies a VPN. |
ip-address |
IPv4 (network layer) address for which a permanent entry is added to the ARP cache. Enter the IPv4 address in a four-part dotted-decimal format that corresponds to the local data-link address (a 32-bit address). |
hardware-address |
Hardware (data link layer) address that the IPv4 address is linked to. Enter the local data-link address (a 48-bit address), such as 0800.0900.1834. |
encapsulation-type |
Encapsulation type. The encapsulation types are: For Ethernet interfaces, this is typically the arpa keyword. |
alias |
(Optional) Causes the software to respond to ARP requests as if it were the owner of both the specified IP address and hardware address, whether proxy ARP is enabled or not. |
No entries are permanently installed in the ARP cache.
Release |
Modification |
---|---|
Release 3.2 |
This command was supported. |
Release 3.3.0 |
The vrf keyword and vrf-name argument were added. The encapsulation information was added. |
The software uses ARP cache entries to translate 32-bit IP addresses into 48-bit hardware addresses.
Because most hosts support dynamic resolution, you generally need not specify static ARP cache entries.
Static entries are permanent entries that map a network layer address (IPv4 address) to a data-link layer address (MAC address). If the alias keyword is specified when creating the entry, the interface to which the entry is attached will act as if it is the owner of the specified addresses, that is, it will respond to ARP request packets for this network layer address with the data link layer address in the entry.
The software does not respond to any ARP requests received for the specified IP address unless proxy ARP is enabled on the interface on which the request is received. When proxy ARP is enabled, the software responds to ARP requests with its own local interface hardware address.
To remove all nonstatic entries from the ARP cache, enter the clear arp-cache in EXEC mode.
Task ID |
Operations |
---|---|
cef |
read, write |
The following is an example of a static ARP entry for a typical Ethernet host:
RP/0/0/CPU0:router# configure RP/0/0/CPU0:router(config)# arp 192.168.7.19 0800.0900.1834 arpa
Command |
Description |
---|---|
Deletes all dynamic entries from the ARP cache. |
|
Displays the ARP cache. |
To delay purging Address Resolution Protocol (ARP) entries when an interface goes down, use the arp purge-delay command in interface configuration mode. To turn off the purge delay feature, use the no form of this command.
arp purge-delay value
no arp purge-delay value
v alue |
Sets the purge delay time in seconds. Range is 1 to 65535. |
Default value is off.
Interface configuration
Release |
Modification |
---|---|
Release 3.4.0 |
This command was introduced. |
Use the arp purge-delay command to delay purging ARP entries when an interface goes down. If the interface comes up within the delay time, then the ARP entries are restored to prevent packet loss with Equal Cost Multipath (ECMP) configured.
Task ID |
Operations |
---|---|
cef |
read, write |
RP/0/0/CPU0:router# configure RP/0/0/CPU0:router(config)# interface MgmtEth 0/RP1/CPU0/0 RP/0/0/CPU0:router(config-if)# arp purge-delay 50
To specify how long dynamic entries learned on an interface remain in the Address Resolution Protocol (ARP) cache, enter the arp timeout command in interface configuration mode. To remove the arp timeout command from the configuration file and restore the system to its default condition with respect to this command, enter the no form of this command.
arp timeout seconds
no arp timeout seconds
seconds |
Indicates the time, in seconds, for which an entry remains in the ARP cache. Range is 30 to 4294967295. |
Entries remain in the ARP cache for 14,400 seconds (4 hours).
Interface configuration
Release |
Modification |
---|---|
Release 3.2 |
This command was supported. |
This command is ignored when issued on interfaces that do not use ARP. Also, ARP entries that correspond to the local interface or that are statically configured by the user never time out.
The arp timeout command applies only to the interface that is entered. When the timeout is changed for an interface the change applies only to that interface.
The show interfaces command displays the ARP timeout value in hours:minutes:seconds, as follows:
ARP type: ARPA, ARP Timeout 04:00:00
Task ID |
Operations |
---|---|
cef |
read, write |
RP/0/0/CPU0:router# configure RP/0/0/CPU0:router(config)# interface MgmtEth 0/RP1/CPU0/0 RP/0/0/CPU0:router(config-if)# arp timeout 3600
Command |
Description |
---|---|
Deletes all dynamic entries from the ARP cache. |
|
Displays the ARP cache. |
|
show interfaces |
Displays statistics for all interfaces configured on the networking device. For information on using the show interfaces command, see Cisco IOS XR software Interface and Hardware Component Command Reference. |
To delete all dynamic entries from the Address Resolution Protocol (ARP) cache, clear the fast-switching cache, and clear the IP route cache, use the clear arp-cache command in EXEC mode.
clear arp-cache { traffic type interface-path-id | location node-id }
No default behavior or values
Release |
Modification |
---|---|
Release 3.2 |
This command was introduced. |
Release 3.3.0 |
The location keyword and node-id argument were made mandatory. |
When issued without keywords or arguments, the clear arp-cache command clears all entries in the ARP cache.
Task ID |
Operations |
---|---|
cef |
execute |
RP/0/0/CPU0:router# clear arp-cache traffic gigabitEthernet 0/1/5/1 location 0/1/CPU0
RP/0/0/CPU0:router# clear arp-cache location 0/1/CPU0
Command |
Description |
---|---|
Adds a permanent entry in the ARP cache. |
|
Displays the ARP cache. |
To enable local proxy Address Resolution Protocol (ARP) on an interface, enter the local-proxy-arp command in interface configuration mode. To disable local proxy ARP on the interface, enter the no form of this command.
local-proxy-arp
no local-proxy-arp
This command has no keywords or arguments.
Local proxy ARP is disabled on all interfaces.
Interface configuration
Release |
Modification |
---|---|
Release 4.0.0 |
This command was introduced. |
When local proxy ARP is enabled, the networking device responds to ARP requests that meet all the following conditions:
The target IP address in the ARP request, the IP address of the ARP source, and the IP address of the interface on which the ARP request is received are on the same Layer 3 network.
The next hop for the target IP address is through the same interface as the request is received.
Typically, local proxy ARP is used to resolve MAC addresses to IP addresses in the same Layer 3 network such as, private VLANs that are Layer 2-separated. Local proxy ARP supports all types of interfaces supported by ARP and unnumbered interfaces.
Using the no form of the command removes the specified command from the configuration file and restores the system to its default condition with respect to the command.
Task ID |
Operations |
---|---|
cef |
read, write |
RP/0/0/CPU0:router#(config)# interface TenGigE 0/0/0/0 RP/0/0/CPU0:router#(config-if)# local-proxy-arp
To enable proxy Address Resolution Protocol (ARP) on an interface, enter the proxy-arp command in interface configuration mode. To disable proxy ARP on the interface, enter the no form of this command.
proxy-arp
no proxy-arp
This command has no keywords or arguments.
Proxy ARP is disabled on all interfaces.
Interface configuration
Release |
Modification |
---|---|
Release 3.2 |
This command was introduced. |
When proxy ARP is disabled, the networking device responds to ARP requests received on an interface only if one of the following conditions is met:
When proxy ARP is enabled, the networking device also responds to ARP requests that meet all of the following conditions:
Using the no form of the command removes the specified command from the configuration file and restores the system to its default condition with respect to the command.
Task ID |
Operations |
---|---|
cef |
read, write |
RP/0/0/CPU0:router#(config)# interface MgmtEth 0/RP1/CPU0/0 RP/0/0/CPU0:router#(config-if)# proxy-arp
To display the Address Resolution Protocol (ARP), enter the show arp command in EXEC mode.
show arp vrf vrf-name [traffic] [ ip-address | hardware-address | interface-path-id ] [traffic] location node-id
vrf |
(Optional) Specifies VPN routing and forwarding (VRF) instance. |
||
vrf-name |
(Optional) VRF instance that identifies a VPN. |
||
ip-address |
(Optional) The ARP entries you want to display. |
||
location node-id |
(Optional) Displays the ARP entry for a specific location. The node-id argument is entered in the rack/slot/module notation. |
||
hardware-address |
(Optional) The ARP entries that match the 48-bit MAC address are displayed. |
||
traffic |
(Optional) Displays ARP traffic statistics. |
||
interface- path-id |
Either a physical interface instance or a virtual interface instance as follows:
For more information about the syntax for the router, use the question mark (?) online help function. |
The active RP is the default location.
Release |
Modification |
---|---|
Release 3.2 |
This command was introduced. |
Release 3.3.0 |
The vrf keyword and vrf-name argument were added. |
ARP establishes correspondences between network addresses (an IP address, for example) and Ethernet hardware addresses. A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded.
For show arp interface-type interface-instance form, the location node-id keyword and argument is mandatory for Bundle and VLAN-on-Bundle interfaces to indicate which location the cache entries for the bundle should be displayed. For physical interfaces, specifying the location node-id keyword and argument is optional since the interface can only exist on one node.
Task ID |
Operations |
---|---|
cef |
read |
The following is sample output from the show arp command with no location specified:
RP/0/0/CPU0:router# show arp ------------------------------------------------------------------------------- 0/3/CPU0 ------------------------------------------------------------------------------- Address Age Hardware Addr State Type Interface 192.4.1.1 - 000c.cfe6.3336 Interface ARPA 0/3/1/3 192.4.1.2 01:37:50 0000.c004.0102 Dynamic ARPA 0/3/1/3 2.1.4.2 - 000c.cfe6.33b5 Interface ARPA 0/3/3/4 2.1.0.2 - 000c.cfe6.33b1 Interface ARPA 0/3/3/0 2.1.0.1 00:37:56 000a.8b08.857a Dynamic ARPA 0/3/3/0 2.1.4.1 01:37:51 000a.8b08.857e Dynamic ARPA 0/3/3/4 211.11.1.1 - 000c.cfe6.32fa Interface ARPA FastEthernet0/3/0/6 2.1.5.2 - 000c.cfe6.33b6 Interface ARPA FastEthernet0/3/3/5 2.1.1.2 - 000c.cfe6.33b2 Interface ARPA FastEthernet0/3/3/1 2.1.1.1 01:37:51 000a.8b08.857b Dynamic ARPA FastEthernet0/3/3/1 2.1.5.1 01:37:50 000a.8b08.857f Dynamic ARPA FastEthernet0/3/3/5 ------------------------------------------------------------------------------- 0/2/CPU0 ------------------------------------------------------------------------------- Address Age Hardware Addr State Type Interface 5.6.9.1 01:11:55 0003.fe4c.0bff Dynamic ARPA MgmtEth0/2/CPU0/0 5.6.25.6 01:09:29 000c.cfe6.2000 Dynamic ARPA MgmtEth0/2/CPU0/0 5.6.5.10 00:39:58 0009.7b49.0bff Dynamic ARPA MgmtEth0/2/CPU0/0
The following is sample output from the show arp command with the interface-type interface-instance argument:
RRP/0/0/CPU0:router# show arp MgmtEth 0/RP1/CPU0/0
Address Age Hardware Addr State Type Interface
10.4.9.2 00:35:55 0030.7131.abfc Dynamic ARPA MgmtEth0/RP1/CPU0/0
10.4.9.1 00:35:55 0000.0c07.ac24 Dynamic ARPA MgmtEth0/RP1/CPU0/0
10.4.9.99 00:49:12 0007.ebea.44d0 Dynamic ARPA MgmtEth0/RP1/CPU0/0
10.4.9.199 - 0001.c9eb.dffe Interface ARPA MgmtEth0/RP1/CPU0/0
The following is sample output from the show arp command with the hardware-address designation:
RP/0/0/CPU0:router# show arp 0005.5f1d.8100
Address Age Hardware Addr State Type Interface
172.16.7.2 - 0005.5f1d.8100 Interface ARPA 2/0/1/2
The following is sample output from the show arp command with the location keyword and node-id argument:
RP/0/0/CPU0:router# show arp location 0/2/CPU0
Address Age Hardware Addr State Type Interface
192.168.15.1 - 00dd.00ee.00ff Alias ARPA
192.168.13.1 - 00aa.00bb.00cc Static ARPA
172.16.7.1 00:35:49 0002.fc0e.9600 Dynamic ARPA 2/0/1/2
172.16.7.2 - 0005.5f1d.8100 Interface ARPA 2/0/1/2
To display Address Resolution Protocol (ARP) traffic statistics, enter the show arp traffic command in EXEC mode.
show arp traffic [ vrf vrf-name ] [interface-path-id] [ location node-id ]
vrf |
(Optional) Specifies VPN routing and forwarding (VRF) instance. |
||
vrf-name |
(Optional) VRF instance that identifies a VPN. |
||
interface- path-id |
(Optional) Either a physical interface instance or a virtual interface instance as follows:
For more information about the syntax for the router, use the question mark (?) online help function. |
||
location node-id |
(Optional) Displays the ARP entry for a specific location. The node-id argument is entered in the rack/slot/module notation. |
The active RP is the default location.
Release |
Modification |
---|---|
Release 3.7.2 |
This command was introduced. |
ARP establishes correspondences between network addresses (an IP address, for example) and Ethernet hardware addresses. A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded.
For show arp traffic, interface-instance, the locationnode-id keyword and argument is mandatory for Bundle and VLAN-on-Bundle interfaces to indicate which location the cache entries for the bundle should be displayed. For physical interfaces, specifying the location node-id keyword and argument is optional since the interface can only exist on one node.
Task ID |
Operations |
---|---|
cef |
read |
The following is sample output from the show arp traffic command:
RP/0/0/CPU0:router# show arp traffic
ARP statistics:
Recv: 2691 requests, 91 replies
Sent: 67 requests, 2 replies (0 proxy, 1 gratuitous)
Resolve requests rcvd: 1
Resolve requests dropped: 0
Errors: 0 out of memory, 0 no buffers
ARP cache:
Total ARP entries in cache: 4
Dynamic: 3, Interface: 1, Standby: 0
Alias: 0, Static: 0
IP Packet drop count for node 0/0/CPU0: 1
The following is sample output from the show arp traffic command with the location keyword and node-id argument:
RP/0/0/CPU0:router# show arp traffic location 0/2/CPU0
ARP statistics:
Recv: 0 requests, 1 replies
Sent: 0 requests, 2 replies (0 proxy, 2 gratuitous)
Resolve requests rcvd: 0
Resolve requests dropped: 0
Errors: 0 out of memory, 0 no buffers
ARP cache:
Total ARP entries in cache: 4
Dynamic: 1, Interface: 1, Static: 1
Alias: 1, Standby: 0
IP Packet drop count for node 0/2/CPU0: 1
Command |
Description |
---|---|
Adds a permanent entry to the ARP cache. |
|
Deletes all dynamic entries from the ARP cache. |
|
Displays ARP statistics. |