Configuration Guide Configuring DHCPConfiguring DHCP
VRRP Monitoring
In a Virtual Router Redundancy Protocol (VRRP) scenario, Ruijie devices enabled with DHCP provide a command to
monitor the VRRP status of the interface. To an interface configured with VRRP address and VRRP monitoring, a DHCP
server only processes the DHCP clients' request packets from the interface in Master state, and other packets are
discarded. If no VRRP address is configured, the DHCP server does not monitor the VRRP status, and all DHCP packets
are processed. VRRP monitoring is configured on only layer-3 interfaces. It is disabled by default, namely, only the Master
device processes the DHCP service.
IP Address Assignment Based on VLANs, Ports and IP Range
After an IP address pool is deployed, the specified IP address range is assigned based on VLANs and ports. There are
three scenarios. 1. Global configuration. 2. Configuration based on VLANs, ports and IP range. 3. Both 1 and 2. In
scenario 1, the addresses are assigned globally. In scenario 2, the addresses in the specified IP range are assigned only
to the clients of the specified VLANs and ports. In scenario 3, the clients of the specified VLANs and ports are assigned
the addresses in the specified IP range, and the other clients are configured with default global addresses.
Adding Trusted ARP
A trusted ARP prevents gateway ARP spoofing. Ruijie devices enabled with DHCP provide a command for pushing a
trusted ARP while assigning an address. After this function is enabled, DHCP server pushes it while assigning an IP
address to the client to prevent ARP spoofing.
ARP-Based Offline Detection
Ruijie devices enabled with DHCP provide a command to enable ARP-based offline detection. After this function is
enabled, a DHCP server will receive an ARP aging notification when a client gets offline, and start retrieving the client's
address. If the client does not get online within a period of time (5 minutes by default), the DHCP server will retrieve the
address and assign it to another client. If the client gets online again, the address is still valid.
Related Configuration
Enabling DHCP Server Globally
By default, DHCP Server is disabled.
Run the service dhcp command to enable the DHCP Server.
Run the service dhcp command globally to enable DHCP service.
Configuring Address Pool
By default, no address pool is configured.
Run the ip dhcp pool command to configure an IP address range, a gateway and a DNS.
If no address pool is configured, no addresses will be assigned.
4.3.2 DHCP Relay Agent
Working Principle
The destination IP address of DHCP request packets is 255.255.255.255, and these packets are forwarded within a
subnet. To achieve IP address assignment across network segments, a DHCP relay agent is needed. The DHCP relay
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