135Specifying DHCP serversSpecifying DHCP servers on a relay agentTo improve availability, you can specify several DHCP servers on the DHCP relay agent. When theinterface receives request messages from clients, the relay agent forwards them to all DHCPservers.Follow these guidelines when you specify a DHCP server address on a relay agent:• The IP address of any specified DHCP server must not reside on the same subnet as the IPaddress of the relay interface. Otherwise, the clients might fail to obtain IP addresses.• You can specify a maximum of eight DHCP servers.To specify a DHCP server address on a relay agent:Step Command Remarks1. Enter system view. system-view N/A2. Enter interface view. interface interface-typeinterface-number N/A3. Specify a DHCP serveraddress on the relay agent.dhcp relay server-addressip-addressBy default, no DHCP serveraddress is specified on the relayagent.Configuring a DHCP address pool on a DHCP relay agentAbout DHCP address pool on a DHCP relay agentThis feature allows DHCP clients of the same type to obtain IP addresses and other configurationparameters from the DHCP servers specified in the matching DHCP address pool.It applies to scenarios where the DHCP relay agent connects to clients of the same access type butclassified into different types by their locations. In this case, the relay interface typically has no IPaddress configured. You can use the gateway-list command to specify gateway addresses forclients matching the same DHCP address pool and bind the gateway addresses to the device's MACaddress. Example network is the IPoE network.Upon receiving a DHCP DISCOVER or REQUEST from a client that matches a DHCP address pool,the relay agent processes the packet as follows:• Fills the giaddr field of the packet with a specified gateway address.• Forwards the packet to all DHCP servers in the matching DHCP address pool.The DHCP servers select a DHCP address pool according to the gateway address.Restrictions and guidelinesIf PPPoE users are in the network, follow these restrictions and guidelines when you configure theDHCP address pool:• Enable the DHCP relay agent to record DHCP relay entries by using the dhcp relayclient-information record command. When a PPPoE user goes offline, the DHCP relay agentcan find a matching relay entry and send a DHCP-RELEASE message to the DHCP server.This mechanism ensures the DHCP server is aware of the releasing of the IP address in atimely manner.• The remote-server command also configures the device as a DHCP relay agent. You do notneed to enable the DHCP relay agent by using the dhcp select relay command.
