MAC Address-Triggered ARP Entry Update
Only the S5720-EI, S5720-HI, S5720I-SI, S5720S-SI, S5720-SI, S5735-S, S5735S-S, S5735-S-I, S5730-HI, S5730S-EI, S5730-SI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6720S-SI, S6720-SI, S6730-H, S6730S-H, S6730-S, and S6730S-S support this function.
Hosts on an Ethernet LAN send and receive Ethernet data frames based on MAC addresses. To map IP addresses to MAC addresses, the Address Resolution Protocol (ARP) is used. When two hosts on different network segments communicate with each other, they need to map IP addresses to MAC addresses and outbound interfaces according to ARP entries.
Generally, the outbound interfaces in the matching MAC address entries and ARP entries are consistent. In Figure 1, the outbound interface in both the MAC address entry and ARP entry is GE0/0/1 at T1. The interface is then changed. At T2, after a packet is received from the peer device, the outbound interface in the MAC address entry is immediately changed to GE0/0/2. However, the outbound interface in the ARP entry remains as GE0/0/1. At T3, the aging time of the ARP entry expires, and the outbound interface in the ARP entry is changed to GE0/0/2 through ARP aging probe. Between T2 and T3, the outbound interface in the ARP entry is unavailable, interrupting communication between devices on different network segments.
MAC address-triggered ARP entry update enables a switch to update the outbound interface in an ARP entry immediately after the outbound interface in the corresponding MAC address entry changes. Figure 2 shows a scenario where MAC address-triggered ARP entry update is enabled. At T2, after the outbound interface in the MAC address entry is changed to GE0/0/2, the outbound interface in the ARP entry is immediately changed to GE0/0/2. This function ensures communication is not interrupted between T2 and T3 due to the incorrect outbound interface in the ARP entry.
The MAC address-triggered ARP entry update function is often used in scenarios where switches in a Virtual Router Redundancy Protocol (VRRP) group connect to servers (see Configuring MAC Address-Triggered ARP Entry Update to Improve VRRP Switchover Performance), or Layer 3 traffic switching scenarios where STP and Smart Link are used.