Netgear FSM726v3 7000 Series Managed Switch Administration Guide for Software - Page 500

NETGEAR Managed Switches Software Administration Manual, Release 8.0 Chapter 29 DHCP L2 Relay DHCP Relay Agents eliminate the necessity of having a DHCP server on each physical network. Relay Agents populate the giaddr field and also append the Relay Agent Information option to the DHCP messages. DHCP servers use this option for IP address and other parameter assignment policies. These DHCP Relay Agents are typically an IP routing aware device and are referred as Layer 3 Relay Agents. In some network configurations, there is a need for Layer 2 devices to append the Relay Agent Information option as they are closer to the end hosts. These Layer 2 devices are typically operating only as bridges for the network and may not have an IPv4 address on the network in question. Lacking a valid IPv4 source address, they cannot relay packets directly to a DHCP server located on another network. These Layer 2 devices append the Relay Agent Information option and broadcast the DHCP message. This chapter provides information about where a Layer 2 Relay Agent fits in and how it is used. Host #1 1/0/5 1/0/6 1/0/4 Layer 2 Switch #1 DHCP Server #1 Host #2 Figure 29-1 29-1 v1.0, October 2009 DHCP L2 Relay