Table Of Contents

ARP Commands on Cisco IOS XR Software

arp

arp timeout

clear arp-cache

proxy-arp

show arp (cache)

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 ip-address hardware-address encapsulation-type [alias]

no arp ip-address hardware-address encapsulation-type [alias]

Syntax Description

ip-address	IP address that owns the ARP cache to which you want to add a permanent entry. Enter the IP address in a four-part dotted-decimal format that corresponds to the local data-link address (a 32-bit address).
hardware-address	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.

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.

If the alias keyword is not specified, the entry is just a static entry and does not learn the new hardware address for that IP address. The software does not respond to any ARP requests received for that 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 for that IP address with its own local interface hardware address.

To remove all nonstatic entries from the ARP cache, enter the clear arp-cache in EXEC mode.

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 (cache)	Displays the ARP cache.

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 4294967. A value of 0 means that entries are never cleared from the cache. The default is 14400.

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.

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 show interfaces command displays the ARP timeout value in hours:minutes:seconds, as follows:

ARP type: ARPA, ARP Timeout 04:00:00

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 (cache)	Displays the ARP cache.
show interfaces	Displays statistics for all interfaces configured on the networking device. Note See the Cisco IOS XR Interface and Hardware Component Command Reference for information on using the show interfaces command.

clear arp-cache

To delete all dynamic entries from the Address Resolution Protocol (ARP) cache, to clear the fast-switching cache, and to clear the IP route cache, enter the clear arp-cache command in EXEC mode.

clear arp-cache [traffic [interface-instance | location node-id]] [location node-id]

Syntax Description

traffic	(Optional) Deletes traffic statistics on the specified interface.
interface-instance	(Optional) ARP entries matching the interface. The interface-instance argument is entered in the rack/slot/module/port notation.
location node-id	(Optional) 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.

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.

Examples

The following example shows how to remove all dynamic entries from the ARP cache and clears the fast-switching cache:

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

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 POS0/2/0/1

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/RP1/CPU0

Related Commands

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

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.

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 (cache)

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

show arp [ip-address [location node-id] | hardware-address [location node-id] | traffic [location node-id | interface-instance] | trace [error [location node-id] | dev [location node-id] | events [location node-id] table [location node-id] packets [location node-id] | [location node-id]] | type instance| location node-id]

Syntax Description

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: •Physical interface instance. Naming notation is rack/slot/module/port and a slash mark between values is required as part of the notation. –rack: Chassis number of the rack. –slot: Physical slot number of the 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.
trace	(Optional) Displays ARP entries in the buffer.
error	(Optional) Displays ARP error logs.
dev	(Optional) Displays ARP internal logs.
events	(Optional) Displays ARP events logs.
table	(Optional) Displays ARP cache logs.
packets	(Optional) Displays ARP packet receive and reply logs.
type instance	(Optional) The interface whose ARP cache you want to display. Enter the interface type, followed by the physical or virtual interface instance. Note Refer to the interface instance description earlier in this table for more information about specifying physical and virtual interface instances. For more information, enter the question mark (?) online help function.

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.

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.

The show arp type instance form of this command does not support the location node-id keyword and argument. This command also displays the ARP table information. The show arp command and the show arp type instance command display the same information.

Examples

The following is sample output from the show arp command:

RP/0/RP0/CPU0:router# show arp

Address         Age        Hardware Addr   State      Type  Interface

10.4.9.2        00:59:32   0030.7131.abfc  Dynamic    ARPA  MgmtEth0/RP0/CPU0/0

10.4.9.1        00:59:32   0000.0c07.ac24  Dynamic    ARPA  MgmtEth0/RP0/CPU0/0

10.4.9.99       00:12:49   0007.ebea.44d0  Dynamic    ARPA  MgmtEth0/RP0/CPU0/0

10.4.9.199      -          0001.c9eb.dffe  Interface  ARPA  MgmtEth0/RP0/CPU0/0

The following is sample output from the show arp command with the type 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 8 describes the significant fields shown in the display.

Table 8 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. Values are: •ARPA •ETLK (EtherTalk) •SMDS
Interface	Displays the interface associated with this network address.
ARP statistics	Displays ARP packet and error statistics.
ARP cache	Displays general information about the IP address and MAC address association entries in the ARP cache.
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.