ARP entry types

An ARP table stores dynamic ARP entries, OpenFlow ARP entries, Rule ARP entries, and static ARP entries.

ARP automatically creates and updates dynamic entries. A dynamic ARP entry is removed when its aging timer expires or the output interface goes down. In addition, a dynamic ARP entry can be overwritten by a static ARP entry.

A static ARP entry is manually configured and maintained. It does not age out and cannot be overwritten by any dynamic ARP entry.

Static ARP entries protect communication between devices because attack packets cannot modify the IP-to-MAC mapping in a static ARP entry.

The device supports the following types of static ARP entries:

• Long static ARP entry—It is directly used for forwarding packets. A long static ARP entry contains the IP address, MAC address, VLAN, and output interface.

• Short static ARP entry—It contains only the IP address and MAC address.

  If the output interface is a VLAN interface, the device sends an ARP request whose target IP address is the IP address in the short entry. If the sender IP and MAC addresses in the received ARP reply match the short static ARP entry, the device performs the following operations:

  • Adds the interface that received the ARP reply to the short static ARP entry.

  • Uses the resolved short static ARP entry to forward IP packets.

• Multiport ARP entry—It contains the IP address, MAC address, and VLAN.

  The device can use a multiport ARP entry that has the same MAC address and VLAN as a multicast or multiport unicast MAC address entry for packet forwarding. A multiport ARP entry is manually configured. It does not age out and cannot be overwritten by any dynamic ARP entry. For more information about multicast MAC, see the IGMP snooping configuration in IP Multicast Configuration Guide.

To communicate with a host by using a fixed IP-to-MAC mapping, configure a short static ARP entry on the device. To communicate with a host by using a fixed IP-to-MAC mapping through an interface in a VLAN, configure a long static ARP entry on the device.

ARP creates OpenFlow ARP entries by learning from the OpenFlow module. An OpenFlow ARP entry does not age out, and it cannot be updated. An OpenFlow ARP entry can be used directly to forward packets. For more information about OpenFlow, see OpenFlow Configuration Guide.

Rule ARP entries can be directly used for packet forwarding. A Rule ARP entry does not age out, and it cannot be updated. It can be overwritten by a static ARP entry.

ARP creates Rule ARP entries by learning from the portal authentication module. For more information about portal authentication, see portal authentication configuration in Security Configuration Guide.