Configuring DHCP Relay DHCP Relay Overview
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 21-4
DHCP Relay Overview
The DHCP Relay service, its corresponding port numbers, and configurable options are as follows:
• DHCP Relay Service: BOOTP/DHCP
• UDP Port Numbers 67/68 for Request/Response
• Configurable options: DHCP server IP address, Forward Delay, Maximum Hops, Forwarding Option,
automatic switch IP configuration
The port numbers indicate the destination port numbers in the UDP header. The DHCP Relay verifies
whether the forward delay time (specified by the user) has elapsed before sending the packet down to
UDP with the destination IP address replaced by the address (also specified by the user).
If the relay is configured with multiple IP addresses, then the packet is sent to all IP address destinations.
The DHCP Relay also verifies that the maximum hop count has not been exceeded. If the forward delay
time is not met or the maximum hop count is exceeded, the BOOTP/DHCP packet is discarded by the
DHCP Relay.
The forwarding option allows you to specify if the relay must operate in the standard and per-VLAN-only
mode. The standard mode forwards all DHCP packets on a global relay service. The per-VLAN-only
mode forwards DHCP packets that originate from a specific VLAN. See “Setting the Relay Forwarding
Option” on page 21-10 for more information.
An additional function provided by the DHCP Relay service enables automatic IP address configuration
for default VLAN 1 when an unconfigured switch boots up. If this function is enabled, the switch
broadcasts a BootP or a DHCP request packet at boot time. When the switch receives an IP address from a
BootP/DHCP server, the address is assigned to default VLAN 1. See “Enabling Automatic IP
Configuration” on page 21-11 for more information.
Alternately, the relay function can be provided by an external router connected to the switch; in this case,
the relay is configured on the external router.
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