IP Addresses and Services Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

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IP Addresses and Services Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

ARP cache entries

Updated: August 12, 2026

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Explains how ARP cache entries retain IP-to-hardware-address mappings and when to define a permanent static entry for consistent address translation.

An ARP cache entry is an address correspondence that

  • maps a network address, such as an IP address, to an Ethernet hardware address

  • lets the system retrieve an existing mapping without repeating address resolution, and

  • remains in the cache dynamically for a predetermined time or permanently when configured as a static entry.

Static ARP cache entries

Use this reference to understand the purpose and behavior of static ARP cache entries.

Most hosts support dynamic address resolution, so static ARP entries are generally unnecessary.

When a permanent mapping is required, you can configure a global static entry. The entry persists until you explicitly remove it.

Cisco IOS XR software uses the static entry to translate a 32-bit IP address into a 48-bit hardware address.

Define a static ARP cache entry

Use a static ARP cache entry when the system must retain a specific IP-to-MAC address mapping until you explicitly remove it.

The example maps IP address 203.0.113.2 to MAC address 0010.9400.000c.

Before you begin

Identify the IP address and MAC address for the permanent mapping.

Follow these steps to define a static ARP cache entry.

Procedure

  1. Define the static mapping between the IP address and the MAC address in global configuration mode.

    Example:

    Router# configure
Router(config)# arp 203.0.113.2 0010.9400.000c ARPA
Router(config)# commit

  2. Display the running ARP configuration.

    Example:

    Router# show running-config arp
arp vrf default 203.0.113.2 0010.9400.000c ARPA

  3. Verify that the ARP entry state is Static.

    Example:

    Router# show arp location 0/0/CPU0
Address       Age  Hardware Addr    State      Type  Interface
203.0.113.1   -    ea28.5f0b.8024  Interface  ARPA  HundredGigE0/0/0/9
203.0.113.2   -    0010.9400.000c  Static     ARPA  HundredGigE0/0/0/9