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DHCP relay can not only send DHCP broadcasting packets to the specified DHCP servers,
but can also send other specified UDP broadcast packet to specified servers.
11.3.1 DHCP Relay Configuration Task Sequence
1. Enable DHCP relay.
2. Configure DHCP relay to forward DHCP broadcast packet.
3. Configure DHCP relay to forward other UDP broadcast packet.
4. Disable DHCP relay from forwarding DHCP broadcast packet.
1. Enable DHCP relay.
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 <port>
no ip forward-protocol udp <port>
The UDP port 67 is used for DHCP broadcast
packet forwarding.
Interface 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.
3. Configure DHCP relay to forward other UDP broadcast packet.
Command Explanation
Global Mode
ip forward-protocol udp <port>
no ip forward-protocol udp <port>
Specify the DHCP relay forwarding protocol by
setting UDP port; the “no ip forward-protocol
udp <port>” command cancels the setting.
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.
4. Disable DHCP relay from forwarding DHCP broadcast packet.
Command Explanation
Global Mode
ip dhcp relay information policy
drop
no ip dhcp relay information
policy drop
When layer 3 switches are used as DHCP
relays, this command sets the relay
forwarding policy to drop DHCP packets; the
“no ip dhcp relay information policy drop”
command allows DHCP packets forwarding.
11.3.2 DHCP Relay Configuration Command