Table Of Contents

ARP Commands on Cisco IOS XR Software

arp

arp purge-delay

arp timeout

clear arp-cache

proxy-arp

show arp

ARP Commands on Cisco IOS XR Software

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This chapter describes the commands used to configure and monitor the Address Resolution Protocol (ARP).

arp

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]

Syntax Description

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: •arpa •srp •srpa •srpb 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.

Defaults

No entries are permanently installed in the ARP cache.

Command Modes

Global configuration

Command History

Release	Modification
Release 2.0	This command was introduced on the Cisco CRS-1.
Release 3.0	No modification.
Release 3.2	This command was supported on the Cisco XR 12000 Series Router.
Release 3.3.0	The vrf keyword and vrf-name argument were added. The encapsulation information was added.
Release 3.4.0	No modification.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

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

Task ID	Operations
cef	read, write

Examples

The following is an example of a static ARP entry for a typical Ethernet host:

RP/0/RP0/CPU0:router# configure

RP/0/RP0/CPU0:router(config)# arp 192.168.7.19 0800.0900.1834 arpa

Related Commands

Command	Description
clear arp-cache	Deletes all dynamic entries from the ARP cache.
show arp	Displays the ARP cache.

arp purge-delay

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

Syntax Description

purge-delay value

Sets the purge delay time in seconds. Range is 1 to 65535.

Defaults

Default value is off.

Command Modes

Interface configuration

Command History

Release	Modification
Release 3.4.0	This command was introduced on the Cisco CRS-1.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

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

Task ID	Operations
cef	read, write

Examples

The following is an example of setting the purge delay to 50 seconds:

RP/0/RP0/CPU0:router# configure

RP/0/RP0/CPU0:router(config)# interface MgmtEth 0/RP1/CPU0/0

RP/0/RP0/CPU0:router(config-if)# arp purge-delay 50

arp timeout

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

Syntax Description

seconds

Indicates the time, in seconds, for which an entry remains in the ARP cache. Range is 30 to 4294967295.

Defaults

Entries remain in the ARP cache for 14,400 seconds (4 hours).

Command Modes

Interface configuration

Command History

Release	Modification
Release 2.0	This command was introduced on the Cisco CRS-1.
Release 3.0	No modification.
Release 3.2	This command was supported on the Cisco XR 12000 Series Router.
Release 3.3.0	No modification.
Release 3.4.0	No modification.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

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

Task ID	Operations
cef	read, write

Examples

The following example shows how to set the ARP timeout to 3600 seconds to allow entries to time out more quickly than the default:

RP/0/RP0/CPU0:router# configure

RP/0/RP0/CPU0:router(config)# interface MgmtEth 0/RP1/CPU0/0

RP/0/RP0/CPU0:router(config-if)# arp timeout 3600

Related Commands

Command	Description
clear arp-cache	Deletes all dynamic entries from the ARP cache.
show arp	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 Interface and Hardware Component Command Reference.

clear arp-cache

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 {interface-type interface-instance} | location node-id}

Syntax DescriptionI

traffic	(Optional) Deletes traffic statistics on the specified interface.
interface-type	Interface type. For more information, use the question mark (?) online help function.
interface-instance	Either a physical interface instance or a virtual interface instance as follows: •Physical interface instance. Naming notation is rack/slot/module/port and a slash between values is required as part of the notation. –rack: Chassis number of the rack. –slot: Physical slot number of the modular services card or line card. –module: Module number. A physical layer interface module (PLIM) is always 0. –port: Physical port number of the interface. Note In references to a Management Ethernet interface located on a route processor card, the physical slot number is alphanumeric (RP0 or RP1) and the module is CPU0. Example: interface MgmtEth0/RP1/CPU0/0. •Virtual interface instance. Number range varies depending on interface type. For more information about the syntax for the router, use the question mark (?) online help function.
location node-id	Clears the ARP entries for a specified location. The node-id argument is entered in the rack/slot/module notation.

Defaults

No default behavior or values

Command Modes

EXEC

Command History

Release	Modification
Release 2.0	This command was introduced on the Cisco CRS-1.
Release 3.0	No modification.
Release 3.2	This command was supported on the Cisco XR 12000 Series Router.
Release 3.3.0	The location keyword and node-id argument were made mandatory.
Release 3.4.0	No modification.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

When issued without keywords or arguments, the clear arp-cache command clears all entries in the ARP cache.

Task ID

Task ID	Operations
cef	execute

Examples

The following example shows how to remove traffic statistic entries from the ARP cache that match the specified interface:

RP/0/RP0/CPU0:router# clear arp-cache traffic gigabitEthernet 0/1/5/1 location 0/1/CPU0

The following example shows how to remove entries from the ARP cache that match the specified location:

RP/0/RP0/CPU0:router# clear arp-cache location 0/1/CPU0

Related Commands

Command	Description
arp	Adds a permanent entry in the ARP cache.
show arp	Displays the ARP cache.

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

Syntax Description

This command has no arguments or keywords.

Defaults

Proxy ARP is disabled on all interfaces.

Command Modes

Interface configuration

Command History

Release	Modification
Release 2.0	This command was introduced on the Cisco CRS-1.
Release 3.0	No modification.
Release 3.2	This command was supported on the Cisco XR 12000 Series Router.
Release 3.3.0	No modification.
Release 3.4.0	No modification.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

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:

•The target IP address in the ARP request is the same as the interface IP address on which the request is received.

•The target IP address in the ARP request has a statically configured ARP alias.

When proxy ARP is enabled, the networking device also responds to ARP requests that meet all of the following conditions:

•The target IP address is not on the same physical network (LAN) on which the request is received.

•The networking device has one or more routes to the target IP address.

•All of the routes to the target IP address go through interfaces other than the one on which the request is received.

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

Task ID	Operations
cef	read, write

Examples

The following example shows how to enable proxy ARP on MgmtEth interface 0/RP1/CPU0/0:

RP/0/RP0/CPU0:router(config)# interface MgmtEth 0/RP1/CPU0/0

RP/0/RP0/CPU0:router(config-if)# proxy-arp

show arp

To display the Address Resolution Protocol (ARP) , enter the show arp command in EXEC mode.

show arp [vrf vrf-name] [ip-address [location node-id] | hardware-address [location node-id] | traffic [location node-id | interface-instance]

Syntax Description

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-instance	Either a physical interface instance or a virtual interface instance as follows: •Physical interface instance. Naming notation is rack/slot/module/port and a slash between values is required as part of the notation. –rack: Chassis number of the rack. –slot: Physical slot number of the modular services card or line card. –module: Module number. A physical layer interface module (PLIM) is always 0. –port: Physical port number of the interface. Note In references to a Management Ethernet interface located on a route processor card, the physical slot number is alphanumeric (RP0 or RP1) and the module is CPU0. Example: interface MgmtEth0/RP1/CPU0/0. •Virtual interface instance. Number range varies depending on interface type. For more information about the syntax for the router, use the question mark (?) online help function.

Defaults

The active RP is the default location.

Command Modes

EXEC

Command History

Release	Modification
Release 2.0	This command was introduced on the Cisco CRS-1.
Release 3.0	No modification.
Release 3.2	This command was supported on the Cisco XR 12000 Series Router.
Release 3.3.0	The vrf keyword and vrf-name argument were added.
Release 3.4.0	No modification.
Release 3.5.0	No modification.
Release 3.6.0	No modification.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes the proper task IDs. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of the Cisco IOS XR System Security Configuration Guide.

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

Task ID	Operations
cef	read

Examples

The following is sample output from the show arp command with no location specified:

RP/0/RP0/CPU0:router# show arp

-------------------------------------------------------------------------------

0/3/CPU0

-------------------------------------------------------------------------------

Address         Age        Hardware Addr   State      Type  Interface

192.4.1.1       -          000c.cfe6.3336  Interface  ARPA GigabitEthernet0/3/1/3

192.4.1.2       01:37:50   0000.c004.0102  Dynamic    ARPA GigabitEthernet0/3/1/3

2.1.4.2         -          000c.cfe6.33b5  Interface  ARPA FastEthernet0/3/3/4

2.1.0.2         -          000c.cfe6.33b1  Interface  ARPA FastEthernet0/3/3/0

2.1.0.1         00:37:56   000a.8b08.857a  Dynamic    ARPA FastEthernet0/3/3/0

2.1.4.1         01:37:51   000a.8b08.857e  Dynamic    ARPA FastEthernet0/3/3/4

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:

RP/0/RP0/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/RP0/CPU0:router# show arp 0005.5f1d.8100

Address Age Hardware Addr State Type Interface 

172.16.7.2 - 0005.5f1d.8100 Interface ARPA GigabitEthernet2/0/1/2 

The following is sample output from the show arp command with the location keyword and node-id argument:

RP/0/RP0/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 GigabitEthernet2/0/1/2 

172.16.7.2 - 0005.5f1d.8100 Interface ARPA GigabitEthernet2/0/1/2 

The following is sample output from the show arp command with the traffic keyword:

RP/0/RP0/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 command with the traffic and location keywords and node-id argument:

RP/0/RP0/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

Table 7 describes the significant fields shown in the display.

Table 7 show arp Field Descriptions 

Field	Description
Address	Displays the network address that corresponds to the hardware address.
Age	Displays the age in hours:minutes:seconds of the cache entry. A hyphen (-) means the address is local.
Hardware Addr	Displays the LAN hardware address of a MAC address that corresponds to the network address.
State	Displays the current state of the cache entry. Values are: •Dynamic •Interface •Standby (for HSRP) •Incomplete •"-" (indicates global static and alias entries)
Type	Displays the encapsulation type the Cisco IOS XR software is using for the network address in this entry. Value is ARPA .
Interface	Displays the interface associated with this network address.
ARP statistics	Displays ARP packet and error statistics.
Recv	Displays the numbers of received packets.
Sent	Displays the number of sent packets.
Resolve requests rcvd	Displays the number of IP packets received for resolution.
Resolve requests dropped	Displays the number of dropped IP packets.
Errors	Displays the number of packet errors of each type.
ARP cache	Displays general information about the IP address and MAC address association entries in the ARP cache.
Total ARP entries in cache	Displays the number of arp entries in cache.
Dynamic	Displays the number of entries in dynamic state.
Interface	Displays the number of local ARP interface entries.
Standby	Displays the the number of entries in Standby state.
Alias	Displays the number of active statically configured alias entries.
Static	Displays the number of active statically configured arp entries.
IP Packet drop count for node */*/*	Displays the number of IP packets dropped because the buffer ran out of space before an ARP response was received. Note */*/* represents the node ID in the format rack/slot/module.

Related Commands

Command	Description
arp	Adds a permanent entry to the ARP cache.
clear arp-cache	Deletes all dynamic entries from the ARP cache.