Web Management Guide-R04

Table Of Contents
Chapter 18
| IP Services
Dynamic Host Configuration Protocol
– 704 –
Web Interface
To configure DHCP L3 relay service:
1. Click IP Service, DHCP, L3 Relay.
2. Enter up to five IP addresses for DHCP servers or relay servers in order of
preference for any VLAN.
3. Click Apply.
Figure 474: Configuring DHCP L3 Relay Service
Configuring DHCP
L2 Relay Service with
Option 82
When DHCP L2 relay mode is enabled, use the IP Service > DHCP > L2 Relay page to
configure DHCP relay service for attached host devices, including DHCP option 82
information. DHCP provides an option for sending information about its DHCP
clients to the DHCP server (specifically, the interface on the relay server through
which the DHCP client request was received). Also known as DHCP Relay Option 82,
it allows compatible DHCP servers to use this information when assigning IP
addresses, or to set other services or policies for clients.
Option 82 information contains information which can identify both the relay
agent and the interface through which the DHCP request was received:
The DHCP Relay Information Option Remote ID (RID) is the access node
identifier – a string used to identify the switch to the DHCP server.
The DHCP Relay Information Option Fields are the Option 82 circuit
identification fields (CID – including VLAN ID, stack unit, and port). These fields
identify the requesting device by indicating the interface through which the
relay agent received the request.
If DHCP relay is enabled, and this switch sees a DHCP client request, it inserts its
own IP address into the request so that the DHCP server will know the subnet
where the client is located. Depending on the selected frame format set for the
remote-id, this information may specify the MAC address, IP address, or an arbitrary
string for the requesting device (that is, the relay agent in this context).
By default, the relay agent also fills in the Option 82 circuit-id field with information
indicating the local interface over which the switch received the DHCP client