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Configuration Guide - IP Service

S1720, S2700, S5700, and S6720 V200R012(C00 and C20)

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DHCP policy VLAN, DNS, mDNS gateway, mDNS relay, UDP Helper, IP performance optimization, IPv6, DHCPv6, IPv6 DNS, IPv6 over IPv4 tunnel, and IPv4 over IPv6 tunnel.
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(Optional) Configuring a Distributed VXLAN Gateway as a DHCP Relay Agent

(Optional) Configuring a Distributed VXLAN Gateway as a DHCP Relay Agent


In a distributed VXLAN gateway scenario, the DHCP relay function is configured on VBDIF interfaces of distributed gateways. The value of the GIADDR field carried in a request packet sent from a DHCP relay agent to the DHCP server is the IP address of the VBDIF interface. When returning a response packet, the DHCP server figures out the network segment on which the DHCP client resides based on information of this field. However, the response packet from the DHCP server may be forwarded to other distributed gateways (rather than the device that sends the request packet) because IP addresses of VBDIF interfaces on distributed gateways are the same. As a result, the user cannot obtain an IP address.

To resolve the preceding problem, you can enable the re-routing function for DHCP relay agents on VBDIF interfaces of the distributed gateways. After this function is enabled, when a DHCP relay agent sends a request packet, the VTEP IP address of the local device, functioning as the return IP address, is carried in the Option82 field; when a DHCP relay agent returns a response packet, the VTEP IP address of the local device is also carried in the packet. When processing a response packet from the DHCP server, the DHCP relay agent figures out whether the response packet corresponds to the request packet sent from the local device based on the return IP address carried in the packet. If so, the DHCP relay agent forwards the packet to the client. If not, the DHCP relay agent performs re-routing based on the return IP address to forward the response packet to the corresponding distributed gateway through a VXLAN tunnel.


Only the S5720HI, S5730HI, S6720HI, S6720S-EI, and S6720EI support this function.


Because the return IP address is carried in the Option82 field, you need to perform the following operations:
  1. Run the dhcp option82 vendor-specific format vendor-sub-option 2 ip-address ip-address command in the system view to use the Sub Option2 field that is customized by the vendor in the Option82 field to carry the VTEP IP address of the local device.
  2. Run the dhcp option82 encapsulation vendor-specific-id command in the BD view to insert the sub-option customized by the vendor into the Option82 field.
  3. Run the dhcp option82 { insert | rebuild } enable command in the BD view to configure the Option82 field to be inserted into DHCP packets.
  4. Run the dhcp relay information enable command in the VBDIF interface view to enable the Option 82 function for the DHCP relay agent.


  1. Run system-view

    The system view is displayed.

  2. Run interface vbdif bd-id

    A VBDIF interface is created and the VBDIF interface view is displayed.


    The number of a VBDIF interface must match an existing BD ID.

  3. Run dhcp relay anycast gateway re-route enable

    The re-routing function for the DHCP relay agent on a distributed gateway is enabled.

    By default, the re-routing function for the DHCP relay agent on a distributed gateway is disabled.

Verifying the Configuration

Run the display dhcp relay command to check configuration information about the DHCP relay agent.

Updated: 2018-12-24

Document ID: EDOC1100038342

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