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S12700 V200R012C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Enabling MAC Address-triggered ARP Entry Update

Enabling MAC Address-triggered ARP Entry Update

Context

Devices 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 devices on different network segments communicate with each other, they need to map IP addresses to MAC addresses and outbound interfaces according to ARP entries. 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.

Generally, MAC address entries and ARP entries are consistent. In some scenarios, ARP entries may not be updated immediately after MAC address entries are updated. In Figure 2-12, SwitchA and SwitchB run VRRP to enhance reliability, and the VRRP group functions as the gateways of the server. VRRP packets are transmitted on the direct link between the two switches. The server selects one network interface to send packets. When the server detects a network failure or traffic forwarding failure, it switches traffic to the other interface.
  • SwitchA functions as the master device and the server uses Port1 to send packets. SwitchA learns the ARP entry and MAC entry on Port1, and SwitchB learns the server MAC address on Port2.
  • When the server detects that Port1 is faulty, the server uses Port2 to forward service packets. SwitchA learns the server MAC address on Port2. If the server does not send an ARP Request packet to SwitchA, SwitchA still learns the ARP entry on Port1. In this case, packets sent from SwitchA to the server are forwarded through Port1 until the ARP entry is aged out.
To solve the problem, configure MAC address-triggered ARP entry update on SwitchA and SwitchB. This function enables the switches to update the corresponding ARP entry when the outbound interface in a MAC address entry changes.
Figure 2-12  MAC address-triggered ARP entry update upon a VRRP master/backup switchover

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run mac-address update arp

    The MAC address-triggered ARP entry update function is enabled.

    By default, the MAC address-triggered ARP entry update function is disabled.

    NOTE:
    • This function takes effect only for dynamic ARP entries. Static ARP entries are not updated when the corresponding MAC address entries change.
    • The MAC address-triggered ARP entry update function does not take effect after ARP entry fixing is enabled using the arp anti-attack entry-check enable command.
    • After the MAC address-triggered ARP entry update function is enabled, the switch updates an ARP entry only when the outbound interface in the corresponding MAC address entry changes.

Verifying the Configuration

Run the display current-configuration command to check whether the MAC address-triggered ARP entry update function is enabled.

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Updated: 2019-01-18

Document ID: EDOC1100038103

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