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CLI-based Configuration Guide - IP Service

AR100, AR120, AR160, AR1200, AR2200, AR3200, and AR3600 V300R003

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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Multi-Interface ARP

Multi-Interface ARP

Multi-interface ARP allows devices to connect to network load balance (NLB) servers. NLB is developed by Microsoft for a cluster set up by multiple Windows servers. NLB supports load balancing and redundancy backup between servers in a cluster. When a server in the cluster is faulty, data can be quickly switched. To ensure quick switchover, NLB requires that network devices send service traffic to each server in the cluster. Servers use the same NLB algorithm to determine whether to process the service traffic.

An NLB server can work in unicast, multicast, or IGMP multicast mode. Currently, a device can be connected to the NLB server working in only unicast or multicast mode.

  • When the NLB server works in unicast mode, the cluster MAC address starts with 02bf.
  • When the NLB server works in multicast mode, the cluster MAC address starts with 03bf.

As shown in Figure 2-6, each server in the NLB cluster has its own IP and MAC addresses, and the servers also share the cluster IP and MAC addresses. When the router functioning as the access gateway connects to the NLB cluster, the router needs to send the data packets destined for the cluster IP address to each server in the cluster.

When the Router sends an ARP Request packet to the cluster servers to request the cluster MAC address, all the servers in the cluster send an ARP Reply packet to the Router. In the ARP Reply packet, the source IP and MAC addresses are the cluster IP and MAC addresses. If multi-interface ARP is not configured on the Router, the following problems occur when the Router is connected to the NLB servers:

  • When the NLB servers work in unicast mode, the Router can learn only one outbound interface matching the cluster IP address in the ARP entry. Therefore, the Router can send packets destined for the cluster IP address to only one server in the cluster.
  • When the NLB servers work in multicast mode, the Router receives an ARP Reply packet and does not learn the ARP entry because the source MAC address is a multicast MAC address. If static ARP entries are configured on the Router, only one outbound interface can be specified for binding the cluster IP and MAC addresses. If the Router is enabled to dynamically learn ARP entries with multicast MAC addresses, the Router can learn only one outbound interface. Therefore, the Router can send packets destined for the cluster IP address to only one server in the cluster.

Multi-interface ARP allows the Router to send the packet destined for the cluster IP address to all the servers in the cluster.

Figure 2-6  Network diagram of multi-interface ARP

In multi-interface ARP, the cluster IP and MAC addresses are bound in the static ARP table, and the cluster MAC address and multiple outbound interfaces connecting to NLB servers are bound in the MAC address table. When a device receives a packet destined for the cluster IP address, the device searches the ARP table for the cluster MAC address and VLAN based on the cluster IP address, and searches the matching MAC address table for multiple outbound interfaces based on the cluster MAC address and VLAN. The device then sends the packet through these outbound interfaces to set up connections with the NLB servers.

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Updated: 2019-03-06

Document ID: EDOC1100069333

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