Administrator Guide

Layer-2 and Layer-3 Relay Features 1157
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Layer-2 and Layer-3 Relay Features
Dell Networking N1500, N2000, N3000, and N4000 Series Switches
This chapter describes how to configure the layer-2 (L2) DHCP relay, layer-3
(L3) DHCP relay, and IP Helper features on Dell Networking N-Series
switches.
The topics covered in this chapter include:
• L2 and L3 Relay Overview
• Default L2/L3 Relay Values
• Configuring L2 and L3 Relay Features (Web)
• Configuring L2 and L3 Relay Features (CLI)
• Relay Agent Configuration Example
L2 and L3 Relay Overview
When a DHCP client and server are in the same IP subnet, they can directly
connect to exchange IP address requests and replies. However, buying and
maintaining a DHCP server on each subnet can be expensive and is often
impractical. The IP Helper/DHCP Relay features on the Dell Networking
N-Series switches can help enable communication between DHCP clients
and DHCP servers that reside in different subnets. Configuring L3 DHCP
relay also enables the bootstrap protocol (BOOTP) relay.
What Is L3 DHCP Relay?
Network infrastructure devices can be used to relay packets between a DHCP
client and server on different subnets. Such a device, a layer-3 relay agent, is
often a router or L3 switch. The L3 relay agent must have an IP interface on
the client subnets and, if it does not have an IP interface on the server’s
subnet, it should be able to route traffic toward the server’s subnet.
The Dell Networking DHCP Relay Agent enables DHCP clients and servers
to exchange DHCP messages across different subnets. The relay agent
receives the requests from the clients, and checks the valid hops and
giaddr
fields in the DHCP request. If the number of hops is greater than the