Static ARP entry for own IP address

Cisco network devices create a static ARP entry in the ARP table for their own IPv4 addresses on their interfaces.

Here is an example:

SW1#show ip arp | include .254
Internet  10.65.10.254            -   08f3.fb39.e346  ARPA   Vlan10

SW1#show run interface Vlan 10

interface Vlan10
 description SERVERS
 ip address 10.65.10.254 255.255.255.0
end

This is not standard ARP behavior as defined by the protocol itself. This is a device/vendor-specific behavior.

There are several reasons why Cisco has chosen to implement ARP in this way, and all of them have to do with the role and functionality of the Cisco device, as an intermediary device and not an end host. The reasons include:

  • Avoid ARP Broadcasts for Local Communication: Network devices need to communicate with themselves in certain situations (i.e. when implementing dynamic routing protocols, validating routing table updates, and performing self-checks with control plane traffic). Having a static ARP entry for its own IP address means it doesn’t need to broadcast an ARP request to resolve its own IP address to a MAC address. This reduces unnecessary ARP traffic on the network and ensures quicker local communication.
  • Prevent ARP Spoofing and Security Attacks: Static ARP entries can protect against certain types of security attacks, such as ARP spoofing or ARP poisoning. By having a static ARP entry for its own IP address, the Cisco device can avoid being tricked into sending traffic to an attacker’s device.
  • Maintain Stability in Critical Network Functions: Some network protocols and features, such as high availability configurations (HSRP, VRRP, GLBP) and certain routing protocols, rely on the device consistently knowing its own MAC and IP address without relying on dynamic ARP resolutions. Static ARP entries ensure that these critical functions operate without interruption.

https://networklessons.com/ip-services/arp-address-resolution-protocol-explained