DELL N3000 User Manual

Configuring L2 and L3 Relay Features

fields in the DHCP request. If the number of hops is greater than the 

configured number, the agent discards the packet. If the 

giaddr field is zero, 

the agent must fill in this field with the IP address of the interface on which 

the request was received. The agent unicasts the valid packets to all 

configured DHCP servers. Each server responds with a unicast BOOTREPLY 

addressed to the relay agent closest to the client as indicated by 

giaddr field. 

Upon reception of the BOOTREPLY from the server, the agent forwards this 

reply as broadcast or unicast on the interface where the BOOTREQUEST 

arrived. This interface can be identified by the 

giaddr field or option 82.

The Dell Networking N2000, N3000, and N4000 series switches DHCP 

component also supports DHCP relay agent options to identify the client 

interface. If configured, the relay agent inserts these options when forwarding 

the request to the server and removes them when sending the reply to the 

clients.
If an interface has more than one IP address, the relay agent uses the primary 

IP address configured as its relay agent IP address.

In Layer 2 switched networks, there may be one or more infrastructure devices 

(for example, a switch) between the client and the L3 Relay agent/DHCP 

server. In this instance, some of the client device information required by the 

L3 Relay agent may not be included in the DHCP packets sent by the DHCP 

client. In this case, an L2 Relay agent can be used to add the information that 

the L3 Relay Agent and DHCP server need to perform their roles in address 

and configuration and assignment.
Before it relays DHCP requests from clients, the switch can add a Circuit ID 

and a Remote ID. These IDs provide information about the circuit and port 

number connected to the client. This information is added as suboptions in 

the DHCP Option 82 packets as defined in sections 3.1 and 3.2 of RFC3046. 

The switch removes this option from packets that it relays from L3 Relay 

agents/DHCP servers to clients.
These sub-options may be used by the DHCP server to affect how it treats the 

client and also may be used by the relay agent to limit broadcast replies to the 

specific circuit or attachment point of the client.