Users Guide

Layer-2 and Layer-3 Relay Features 1229
option domain-name-servers 10.1.218.3,10.1.219.3;
default-lease-time 21600;
max-lease-time 43200;
}
}
}
}
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 EMC 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
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 EMC Networking N-Series switch 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.