Configuring DHCP Relay DHCP Relay Implementation
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 21-8
DHCP Relay Implementation
The OmniSwitch allows you to configure the DHCP Relay feature in one of two ways. You can set up a
global DHCP Relay or you can set up the DHCP Relay based on the DHCP packet from the client. Both of
these choices provide the same configuration options and capabilities. However, they are mutually
exclusive. The following matrix summarizes the options.
Global DHCP
For the global DHCP service, you must identify an IP address for the DHCP server.
Setting the IP Address
The DHCP Relay is enabled on a switch whenever a DHCP server IP address is defined by using the ip
helper address command. There is no separate command for enabling or disabling the relay service. You
must configure DHCP Relay on switches where packets are routed between IP networks. The following
command defines a DHCP server address:
-> ip helper address 125.255.17.11
The DHCP Relay forwards BOOTP/DHCP broadcasts to and from the specified address. If multiple
DHCP servers are used, one IP address must be configured for each server.
To delete an IP address, use the no form of the ip helper address command. The IP address specified
with this syntax is deleted. If an IP address is not specified with this syntax, then all IP helper addresses
are deleted. The following command deletes an IP helper address:
-> no ip helper address 125.255.17.11
Per-VLAN DHCP
For the Per-VLAN DHCP service, you must identify the number of the VLAN that makes the relay
request.
Identifying the VLAN
You can enter one or more server IP addresses to which packets are sent from a specified VLAN. Do this
by using the ip helper vlan address command. The following syntax identifies the IP address
125.255.17.11 as the DHCP server for VLAN 3:
-> ip helper address 125.255.17.11 vlan 3
The following syntax identifies two DHCP servers for VLAN 4 at two different IP addresses:
-> ip helper address 125.255.17.11 125.255.18.11 vlan 4
Per-VLAN DHCP Relay Global DHCP Relay Effect
Disabled Disabled DHCP Request is flooded within its VLAN
Disabled Enabled DHCP Request is relayed to the Global Relay
Enabled Disabled DHCP Request is relayed to the Per-VLAN Relay
Enabled Enabled N/A
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