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Configuration Guide - IP Service

CloudEngine 8800, 7800, 6800, and 5800 V200R002C50

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DNS, IP performance optimization, IPv6, DHCPv6, and IPv6 DNS.
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ARP Gateway Proxy

ARP Gateway Proxy

NOTE:

Only the CE6850HI, CE6850U-HI, CE6851HI, CE6855HI, CE6856HI, CE6860EI, CE6870EI, CE7850EI, CE7855EI, CE8850EI, and CE8860EI support the function.

Possible Causes

To prevent Layer 2 users within a bridge domain (BD) from directly communicating with each other, enable the gateway proxy function. This function directs traffic from a user to the gateway, and the gateway monitors Layer 2 traffic, securing traffic forwarding.

Implementation Process

After gateway proxy is enabled, the MAC address in ARP reply packets will be the MAC address of the destination Layer 3 gateway, and traffic will be diverted to the Layer 3 gateway. With Figure 2-8, the following example describes the implementation process of ARP gateway proxy for Device A that functions as a Layer 3 gateway.
Figure 2-8  Implementation of ARP gateway proxy

As shown in the preceding figure, Host A needs to communicate with Host B.
  1. ARP entry learning process

    • Host A sends an ARP request packet for the MAC address of Host B. The destination IP address of the ARP request packet is 10.10.10.2, and the destination MAC address is all 0s. The ARP request packet is then encapsulated and sent out as an Ethernet packet.

    • Device A identifies the ARP request packet and checks whether gateway proxy is enabled.
      • If gateway proxy is enabled, Device A replies with an ARP reply packet where the source IP address is 10.10.10.2 and the source MAC address is 3-3-3 (MAC address of Device A, used to prevent Host A and Host B from direct Layer 2 communication).
      • If gateway proxy is disabled, Device A follows the common process.
      NOTE:
      The prerequisite for using gateway proxy is that ARP broadcast suppression is enabled.
  2. Data packet forwarding process

    • HostA sends a data packet to HostB. In the data packet, the source IP address is 10.10.10.1, the source MAC address is 1-1-1, the destination IP address is 10.10.10.2, and the destination MAC address is 3-3-3.

    • Upon receipt of the data packet with the MAC address as 3-3-3, DeviceA removes the Layer 2 header and performs Layer 3 processing. Then, DeviceA searches for the IP forwarding table based on the destination IP address 10.10.10.2 and sends the data packet to HostB. At this point, the destination IP address of the data packet is 10.10.10.2, the destination MAC address 4-4-4, the source MAC address 3-3-3, and the source IP address 10.10.0.0.

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Updated: 2019-03-21

Document ID: EDOC1000166635

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