DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet Switch User Manual
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The DHCP Relay folder contains six windows regarding the DHCP r ela y funct ions on the Switch . T he DH CP windo ws
include DHCP Relay Global Settings, DHCP Relay Interface Settings, DHCP Relay Option 60 Default Settings,
DHCP Relay Option 60 Settings, DHCP Realy Option 61 Default Settings and DHCP Relay Option 61 Settings.
DHCP Relay Global Settings
This window is used to enable and configure DHCP Relay Global Settings on the Switch. The relay hops count lim it
allows the maximum number of hops (routers) that the DHCP messages can be re layed through to be set. If a
packet’s hop count is more than the hop count limit, the packet is dropp ed. T he range is between 1 and 16 hops, with
a default value of 4. The relay time threshold sets the minimum time (in seconds) that the Switch will wait before
forwarding a DHCP REQUEST packet. If the value in the seconds field of the pack et is less than the relay time
threshold, the packet will be dropped. The range is between 0 and 65,536 s econds, with a default value of 0 seconds.
To view this window, click Configuration > DHCP Relay > DHCP Relay Global Settings as shown below:
Figure 2 - 20 DHCP Relay Global Settings window
The following fields can be set:
Parameter Description
DHCP Relay State This field can be toggled between Enabled and Disabled using the pull-down menu. It is
used to enable or disable the DHCP Relay service on the Switch. The def ault is Disabled.
DHCP Relay Hops
Count Limit (1-16) This field allows an entry between 1 and 16 to define the maxim um number of ro uter hops
DHCP messages can be forwarded across. The default hop count is 4.
DHCP Relay Time
Threshold (0-65535) Allows an entry between 0 and 65535 seconds, and defines th e maximum time limit for
routing a DHCP packet. If a value of 0 is entered, the Switch will not process the value in
the seconds field of the DHCP packet. If a non-zero value is entered, the Switc h will use
that value, along with the hop count to determine whether to forward a given DH CP packet.
DHCP Relay Option
82 State This field can be toggled between Enabled and Disabled using the pull-down menu. It is
used to enable or disable the DHCP Agent Information Option 82 on the Switch. The default
is Disabled.
Enabled – When this field is toggle d to Enabled the relay agent will insert and r emove
DHCP relay information (option 82 field) in messages between DHCP servers and clients.
When the relay agent receives the DHCP request, it adds the option 82 inform ation, and the
IP address of the relay agent (if the relay agent is conf igured), to the packet. Once the
option 82 information has been added to the packet it is s ent on to the DH CP s erver. W hen
the DHCP server receives the packet, if the server is capable of option 82, it can im plem ent
policies like restricting the number of IP addresses that can be assigned to a s ingle remote
ID or circuit ID. Then the DHCP server echoes the option 82 fie ld in the DHCP repl y. The
DHCP server unicasts the reply to the back to the relay agent if the request was relayed to
the server by the relay agent. The switch verifies that it originally inserted the option 82
data. Finally, the relay agent removes the option 82 field and forwards t he packet to the
switch port that connects to the DHCP client that sent the DHCP request.
Disabled – If the field is toggled to Disabled t he relay agent will not insert and remove