Manual

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164
to the relay agent field in the DHCPDISCOVER packet on receiving the packet, and forwards
the packet to the specified DHCP server (for DHCP frame format, please refer to RFC2131).
On the receiving the DHCPDISCOVER packets forwarded by DHCP relay, the DHCP server
sends the DHCPOFFER packet via DHCP relay to the DHCP client.
DHCP client chooses a DHCP server and broadcasts a DHCPREQUEST packet, DHCP relay
forwards the packet to the DHCP server after processing.
On receiving DHCPREQUEST, the DHCP server responds with a DHCPACK packet via DHCP
relay to the DHCP client.
DHCP Relay Configuration Task List:
1. Enable DHCP relay.
2. Configure DHCP relay to forward DHCP broadcast packet.
1. Enable DHCP relay.
Command
Explanation
Global Mode
service dhcp
no service dhcp
DHCP server and DHCP relay is enabled as the
DHCP service is enabled.
2. Configure DHCP relay to forward DHCP broadcast packet.
Command
Explanation
Global Mode
ip forward-protocol udp bootps
no ip forward-protocol udp bootps
The UDP port 67 is used for DHCP broadcast
packet forwarding.
Interface Configuration Mode
ip helper-address <ipaddress>
no ip helper-address <ipaddress>
Set the destination IP address for DHCP relay
forwarding; the “no ip helper-address
<ipaddress>“command cancels the setting.
23.4 DHCP Configuration Examples
Scenario 1:
Too save configuration efforts of network administrators and users, a company is using switch
as a DHCP server. The Admin VLAN IP address is 10.16.1.2/16. The local area network for the
company is divided into network A and B according to the office locations. The network
configurations for location A and B are shown below.
PoolA(network 10.16.1.0)
PoolB(network 10.16.2.0)
Device
IP address
Device
IP address
Default gateway
10.16.1.200
Default gateway
10.16.1.200