ARP Commands

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 IP Addresses and Services Configuration Guide for Cisco NCS 6000 Series Routers.

arp

To add a permanent entry in the Address Resolution Protocol (ARP) cache, use the arp command in XR Config 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

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.

Command Default

No entries are permanently installed in the ARP cache.

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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 XR 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 learning

To enable the dynamic learning of ARP entries for a local subnet or all subnets, use the arp learning command.

To disable this command, use the no prefix or the disable option for this command.

arp learning local

no arp learning local

arp learning disable

no arp learning disable

Syntax Description

local

Enables the dynamic learning of ARP entries for local subnets.

When arp learning local is configured on an interface or sub-interface, it learns only the ARP entries from ARP packets on the same subnet.

disable

Disables the dynamic learning of all ARP entries.

Command Default

This command has no keywords or arguments.

Command Modes

Sub-interface configuration mode

Examples

RP/0/RP0/CPU0:router(config)#interface GigabitEthernet 0/0/0/1
RP/0/RP0/CPU0:router(config-if)# ipv4 address 12.1.3.4 255.255.255.0
RP/0/RP0/CPU0:router(config-if)# arp learning local
RP/0/RP0/CPU0:router(config-if)# no shut
RP/0/RP0/CPU0:router(config-if)# commit


RP/0/RP0/CPU0:router(config)# interface GigabitEthernet 0/0/0/1
RP/0/RP0/CPU0:router(config-if)# ipv4 address 12.1.3.4 255.255.255.0
RP/0/RP0/CPU0:router(config-if)# arp learning disable
RP/0/RP0/CPU0:router(config-if)# commit

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

v alue

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

Command Default

Default value is off.

Command Modes

Interface configuration

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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 HundredGigE 0/7/0/0
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 2144448000.

Command Default

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

Command Modes

Interface configuration

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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 HundredGigE 0/7/0/0
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 software 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 XR EXEC mode.

clear arp-cache {traffic type interface-path-id location node-id | location node-id}

Syntax Description

traffic

Deletes statistics on the specified interface.

t ype

Interface type. For more information, use the question mark (?) online help function.

interface- path-id

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 the 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.

Command Default

No default behavior or values

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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

Configuration of the clear arp-cache drop-adjacency command on a particular location is not recommended. If the command is used on a bundle interface, then drop adjacencies may be deleted in one of the line cards and not on other line cards. This scenario can result in entry mismatch. You can use the clear arp-cache drop-adjacency interface location all to remove drop adjacency that is learned for the interface on all the line cards.

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: 


Router# clear arp-cache traffic HundredGigE 0/7/0/0 location 0/1/CPU0
The following example shows how to remove entries from the ARP cache that match the specified location: 


Router# clear arp-cache location 0/1/CPU0

Related Commands

Command

Description

show arp

Displays the ARP cache.

local-proxy-arp

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

Syntax Description

This command has no keywords or arguments.

Command Default

Local proxy ARP is disabled on all interfaces.

Command Modes

Interface configuration

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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

Task ID

Operations

cef

read, write

Examples

The following example shows how to enable local proxy ARP on TenGigE interface 0/0/0/0: 

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

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 keywords or arguments.

Command Default

Proxy ARP is disabled on all interfaces.

Command Modes

Interface configuration

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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 HundredGigE interface 0/7/0/0: 

RP/0/RP0/CPU0:router#(config)# interface HundredGigE 0/7/0/0
RP/0/RP0/CPU0:router#(config-if)# proxy-arp

show arp

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

show arp [traffic] [ip-address | hardware-address | type interface-path-id ] location node-id

Command Default

The active is the default location.

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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. As this time gets over, the records are refreshed after two unicast requests by ARP to the host IP address. If no response is received from the host, then the entry is cleared from the database.

For show arp interface-type interface-instance form, the location and node-id keyword and argument is mandatory for Bundle and VLAN-on-Bundle interfaces. These keywords and arguments indicate the location for which the cache entries for the bundle are to be displayed. For physical interfaces, specifying the location and 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: 


Router# show arp

-------------------------------------------------------------------------------
0/3/CPU0
-------------------------------------------------------------------------------

Address         Age        Hardware Addr   State      Type  Interface

.4.1.1       -          000c.cfe6.3336  Interface  ARPA HundredGigE0/3/1/3

.4.1.2       01:37:50   0000.c004.0102  Dynamic    ARPA HundredGigE0/3/1/3

.1.4.2         - 000c.cfe6.33b5  Interface  ARPA HundredGigE0/3/3/4

.1.0.2         - 000c.cfe6.33b1  Interface  ARPA HundredGigE0/3/3/0

.1.0.1         00:37:56 000a.8b08.857a  Dynamic    ARPA HundredGigE0/3/3/0

.1.4.1         01:37:51 000a.8b08.857e  Dynamic    ARPA HundredGigE0/3/3/4

.11.1.1     - 000c.cfe6.32fa  Interface  ARPA FastEthernet0/3/0/6

.1.5.2         - 000c.cfe6.33b6  Interface  ARPA FastEthernet0/3/3/5

.1.1.2         - 000c.cfe6.33b2  Interface  ARPA FastEthernet0/3/3/1

.1.1.1         01:37:51 000a.8b08.857b  Dynamic    ARPA FastEthernet0/3/3/1

.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

.6.9.1 01:11:55   0003.fe4c.0bff  Dynamic    ARPA MgmtEth0/2/CPU0/0

.6.25.6 01:09:29   000c.cfe6.2000  Dynamic    ARPA MgmtEth0/2/CPU0/0

.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: 


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: 


Router# show arp 0005.5f1d.8100

Address Age Hardware Addr State Type Interface 
172.16.7.2 - 0005.5f1d.8100 Interface ARPA HundredGigE2/0/1/2

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


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 HundredGigE2/0/1/2 
172.16.7.2 - 0005.5f1d.8100 Interface ARPA HundredGigE2/0/1/2

show arp idb

To display the ARP database statistics for an interface, use the show arp idb command in EXEC mode.

show arp idb interface-name location node-id

Syntax Description

interface-name

Name of the interface
node-id

Location of the interface. LC node for physical interfaces, RP or LC node for virtual interfaces

Command Default

There is no default location, location needs to be provided in the CLI.

Command History

Release

Modification

Release 3.3.0

This command was introduced.

Usage Guidelines

The show arp idb command is useful to verify the IP addresses, Mac address, ARP configuration(s) applied on the interface and the entry statistics.

For show arp idb 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.

Task ID

Task ID

Operations

cef

read

Examples

The following is sample output from the show arp idb command:

RP/0/0/CPU0:ios#show arp idb GigabitEthernet 0/0/0/0 location 0/0/CPU0

Mon Jan 30 10:32:15.387 IST

GigabitEthernet0/0/0/0 (0x00000060):

IDB Client: default

IPv4 address 1.1.1.1, Vrf ID 0x60000000

VRF Name default

Dynamic learning: Enable

Dynamic entry timeout: 14400 secs

Drop adjacency timeout: Disable

Purge delay: off

Cache limit: 128000

Incomplete glean count: 1

Complete glean count: 0

Complete protocol count: 0

Dropped glean count: 0

Dropped protocol count: 0

IPv4 caps added (state up)

MPLS caps not added

Interface not virtual, not client fwd ref,

Proxy arp not configured, not enabled

Local Proxy arp not configured

Packet IO layer is NetIO

Srg Role : DEFAULT

Idb Flag : 49292

IDB is Complete

IDB Flag Description:

[CAPS | COMPLETE | IPV4_CAPS_CREATED | SPIO_ATTACHED |

SPIO_SUPPORTED]

Idb Flag Ext : 0x0

Idb Oper Progress : NONE

Client Resync Time : Jan 30 10:07:10.736787

Total entries : 9

| Event Name | Time Stamp | S, M

| idb-create | Jan 30 10:07:10.784 | 1, 0

| idb-state-up | Jan 30 10:07:10.784 | 0, 0

| caps-state-update | Jan 30 10:07:10.784 | 0, 1

| address-update | Jan 30 10:07:10.784 | 0, 0

| idb-complete | Jan 30 10:07:10.784 | 0, 0

| idb-entry-create | Jan 30 10:07:10.784 | 0, 0

| idb-caps-add | Jan 30 10:07:10.784 | 0, 0

| idb-caps-add-cb | Jan 30 10:07:10.784 | 0, 0

| idb-last-garp-sent | Jan 30 10:07:11.808 | 0, 0

show arp traffic

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

show arp traffic [type interface-path-id ] [location node-id]

Syntax Description

type interface- path-id

(Optional) 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 the interface type.

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.

Command Default

The active RP is the default location.

Command History

Release

Modification

Release 5.0.0

This command was introduced.

Usage Guidelines

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 location node-id keyword and argument is mandatory for Bundle and VLAN-on-Bundle interfaces. These keywords and arguments indicate the location for which the cache entries for the bundle are to be displayed. For physical interfaces, specifying the location node-id keyword and argument is optional because 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 traffic command: 


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: 5
  Dynamic: 3, Interface: 1, Standby: 0
  Alias: 0,   Static: 0, DHCP:0, DropAdj: 1

  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:

Related Commands

Command

Description

clear arp-cache

Deletes all dynamic entries from the ARP cache.

show arp

Displays ARP statistics.