Principles of the DHCP relay feature

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Dynamic Host Configuration Protocol (DHCP) relay includes Layer 2 relay and Layer 3 relay.
If the access device between a DHCP client and the DHCP server is only a bridge device on which the route forwarding function is unavailable or disabled, the DHCP Layer 2 relay function can implement transparent transmission of DHCP packets and the route forwarding function does not need to be configured. Only after the option 82 function is enabled, the DHCP relay device processes the packets, that is, adding or removing option 82 from the received DHCP packets.
The DHCP Layer 3 relay function can forward DHCP packets across network segments, so that DHCP clients can obtain dynamically allocated IP addresses from DHCP servers on other networks. Access devices can implement DHCP server configuration through a server group. A DHCP server group includes one or more DHCP servers. Access devices select a DHCPv4 server group in 3 DHCP relay modes, including the standard mode, option 60 mode, and MAC address mode.
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Method used to configure DHCP relay on the AR
When the DHCP server and DHCP clients are on different network segments, the DHCP relay agent can be configured so that the DHCP server can assign IP addresses to the DHCP clients. Procedure: 1. Configure the router # sysname Router # dhcp enable //Enable the DHCP function. # ip pool ip-pool1 gateway-list 10.10.1.1 //Set the gateway IP address. network 10.10.1.0 mask 255.255.255.128 //Specify the range of IP addresses that can be dynamically allocated in the global address pool. excluded-ip-address 10.10.1.2 //Set the IP address 10.10.1.2 that is not assigned automatically in the address pool. excluded-ip-address 10.10.1.4 //Set the IP address 10.10.1.4 that is not assigned automatically in the address pool. dns-list 10.10.1.2 //Configure the IP address of the DNS server for the DHCP client. nbns-list 10.10.1.4 //Configure the IP address of the NetBIOS server for the DHCP client. lease day 10 hour 12 minute 0 //Set the IP address lease to 10 days and 12 hours. domain-name huawei.com //Set the domain name to huawei.com. static-bind ip-address 10.10.1.5 mac-address fc12-2567-ce34 //Assign a fixed IP address to the PC_AD. # ip pool ip-pool2 gateway-list 10.10.1.129 //Set the gateway IP address. network 10.10.1.128 mask 255.255.255.128 //Specify the range of IP addresses that can be dynamically allocated in the global address pool. dns-list 10.10.1.2 //Configure the IP address of the DNS server for the DHCP client. lease day 5 hour 0 minute 0 //Set the IP address lease to 5 days. domain-name huawei.com //Set the domain name to huawei.com. # interface GigabitEthernet0/0/0 ip address 10.10.1.1 255.255.255.128 dhcp select global //Configure the global address pool mode. # interface GigabitEthernet0/0/1 ip address 10.10.1.129 255.255.255.128 dhcp select global //Configure the global address pool mode. 2. Verify the configuration. Run the display ip pool command on the router to check the IP address pool configuration.

Configure DHCP relay on S series switch
For S series switches (except S1700 switches), when the DHCP server and clients are on different network segments, you can configure a DHCP relay agent to help the DHCP server allocate network parameters to DHCP clients. For S series switches, the DHCP relay agent configuration is the same on all switch models in all versions. For details, see "Example for Configuring the Device as a DHCP Relay (on the Same Network)" and "Example for Configuring the Device as a DHCP Relay (Across a GRE Tunnel)" in Typical Configuration Examples.

Does DHCP relay on S series switch support polling
When functioning as a DHCP relay agent, an S series switch (except S1700 switches) supports the DHCP server polling function since V100R006C00. By default, the DHCP server polling function is disabled. You can enable the DHCP server polling function by running the ip relay address cycle command in the system view.

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