ECS4100 Series Web Management Guide-R07

Table Of Contents
Chapter 19
| IP Services
Dynamic Host Configuration Protocol
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Figure 479: Configuring L3 DHCP Relay Service
Configuring DHCP L2
Relay Service
If the switch is configured to provide L2 DHCP Relay service use the second IP
Service > DHCP > Relay page to configure the L2 DHCP relay service for attached
host devices. To configure L2 or L3 DHCP relay service refer to the CLI Reference
Guide DHCP Relay settings of the CLI Reference Guide - specifically the command:
ip dhcp l2/l3 relay.
If L2 DHCP relay is enabled, and this switch sees a DHCP request broadcast, it will
unicast the request towards the configured server(s). Further Option 82 RID and
CID information can be configured to be included with the unicast DHCP Request
packet. When Option 82 information is configured the switchs policy can be
configured to drop, keep or replace and the extra sub-options sub-types can be
included or excluded. When the server receives the DHCP request, it allocates a free
IP address for the DHCP client from its defined scope for the DHCP client’s subnet,
and sends a DHCP response back to the network segment where this switch is
situated. The switch will then eventually pass the DHCP response received from the
server to the client.
Figure 480: Layer 2 DHCP Relay Service (DHCP server on a separate network
segment)
Command Usage
You must specify the IP address for at least one active DHCP server. Otherwise,
the switchs DHCP relay agent will not be able to forward client requests to a
DHCP server. Up to five DHCP servers can be specified in order of preference.
You can exclude sending the extra subtypes when the Type and Length fields
are not required to be included with the CID and RID of the option 82
information.
Provides IP address
compatible with switch
segment to which client
is attached
DHCP
Server
Switch with L2 DHCP Relay Service
Switch with L3 DHCP Relay Service