Dhcp Relay Overview - Alcatel-Lucent OmniSwitch AOS Release 7 Manual

Configuring DHCP Relay

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
Relay Forwarding Option" on page 17-11
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
tion" on page 17-12
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.
OmniSwitch AOS Release 7 Network Configuration Guide
for more information.
for more information.
"Enabling Automatic IP Configura-
March 2011
DHCP Relay Overview
"Setting the
page 17-5