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Configuration Guide - Ethernet Switching

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, MUX VLAN, 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

The MAC address-triggered ARP entry update enables the switch to update the corresponding ARP entry when the outbound interface in a MAC address entry changes.

On the Ethernet, MAC address entries are used to guide Layer 2 data forwarding. The ARP entries that define the mapping between IP addresses and MAC addresses guide communication between devices on different network segments.

The outbound interface in a MAC address entry is updated by packets, whereas the outbound interface in an ARP entry is updated after the aging time is reached. In this case, the outbound interfaces in the MAC address entry and ARP entry may be different. In Figure 2-11, SwitchA and SwitchB function as gateways of the server and have VRRP enabled to enhance reliability. VRRP packets are transmitted on the directly connected link between the two switches. When the server sends packets, only one network interface is selected to forward packets. When a network fault or traffic exception is detected, another network interface is used.
Figure 2-11 Networking for configuring MAC address-triggered ARP entry update when a VRRP active/backup switchover is performed
  • SwitchA functions as the master device, and the server uses Port2 to send packets. SwitchA learns the ARP entry and MAC address entry on Port2, and SwitchB learns the server MAC address on Port1.
  • When the server detects that Port2 is faulty, the server uses Port1 to forward service packets. SwitchA then learns the server MAC address on Port1. If the server does not send an ARP Request packet to SwitchA, SwitchA still maintains the ARP entry on Port2. In this case, packets sent from SwitchA to the server are still forwarded through Port2 until the ARP entry is aged out.
To solve the problem, configure MAC address-triggered ARP entry update. This function enables the device to update the corresponding ARP entry when the outbound interface in a MAC address entry changes.

In data center virtualization scenarios, when the location of a virtual machine (VM) changes, user traffic on the network may be interrupted if the VM cannot send gratuitous ARP messages promptly to update ARP entries on the gateway. In this case, the device relearns ARP entries by exchanging ARP messages only after ARP entries on the gateway age.

When the VM location is changed after MAC-ARP association is enabled and a gateway's MAC entries are updated upon receipt of Layer 2 user traffic, ARP entries and outbound interface information are updated as follows to accelerate Layer 3 traffic convergence:
  • If ARP entries exist and the outbound interface of MAC entries is inconsistent with that of ARP entries, ARP entries are updated based on MAC entries, and outbound interface information is updated.
  • If ARP entries do not exist, a broadcast suppression table is searched based on MAC entries and ARP probe is re-initiated to update ARP entries and outbound interface information.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run mac-address update arp enable

    MAC address-triggered ARP entry update is enabled.

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

    NOTE:
    • This command takes effect only for dynamic ARP entries. Static ARP entries are not updated when the corresponding MAC address entries change.
    • The mac-address update arp enable command does not take effect after ARP entry fixing is enabled by using the arp anti-attack entry-check { fixed-mac | fixed-all | send-ack } enable command.
    • After the mac-address update arp enable command is run, the switch updates an ARP entry only when the outbound interface in the corresponding MAC address entry changes.
    • By default, MAC address triggered ARP entry update is enabled. If MAC address flapping occurs for more than 10 times, MAC address triggered ARP entry update is disabled. After MAC address flapping is eliminated, MAC address triggered ARP entry update is enabled automatically.

  3. Run commit

    The configuration is committed.

Verifying the Configuration

Run the display current-configuration command to check whether the MAC address-triggered ARP entry update function is enabled. If there are configurations of the undo mac-address update arp enable command, MAC address-triggered ARP entry update is not configured. If there is no configuration of the undo mac-address update arp enable command, MAC address-triggered ARP entry update is configured.

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Updated: 2019-05-08

Document ID: EDOC1100004351

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