H3C Technologies H3C S5560 Series Switches - Manual (Page 18)

3
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 contains the IP address, MAC address, VLAN, and output interface. It is
directly used for forwarding packets.
• Short static ARP entry—It contains only the IP address and MAC address.
{
If the output interface is a Layer 3 Ethernet interface, the short ARP entry can be directly used to
forward packets.
{
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 tasks:
− 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 IP Multicast Configuration Guide.
Configure a short static ARP entry when the device communicates with a host by using a fixed IP-to-MAC
mapping. Configure a long static ARP entry when the device communicates with a host by using a fixed
IP-to-MAC mapping through an interface in a VLAN.
OpenFlow ARP entry
ARP creates OpenFlow ARP entries by learning from the OpenFlow module. An OpenFlow ARP entry
does not age out and cannot be updated. It can be overwritten by a static ARP entry. An OpenFlow ARP
entry can be used directly to forward packets. For more information about OpenFlow, see OpenFlow
Configuration Guide.
Configuring a static ARP entry
A static ARP entry is effective when the device functions correctly. If a VLAN or VLAN interface is deleted,
long static ARP entries in the VLAN are deleted, and resolved short static ARP entries in the VLAN
become unresolved.
A resolved short static ARP entry becomes unresolved upon certain events. For example, it becomes
unresolved when the resolved output interface goes down.
A long static ARP entry is ineffective in either of the following situations:
• The IP address in the entry conflicts with a local IP address.
• No local interface has an IP address in the same subnet as the IP address in the ARP entry.
Follow these guidelines when you configure a long static ARP entry:
• The vlan-id argument must be the ID of an existing VLAN where the ARP entry resides. The specified
Ethernet interface must belong to that VLAN.