D-Link DGS-3700 User Manual download pdf (Page 34)

DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet Switch User Manual

DHCP Relay

The DHCP Relay folder contains six windows regarding the DHCP relay functions on the Switch. The DHCP windows

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 limit

allows the maximum number of hops (routers) that the DHCP messages can be relayed through to be set. If a

packet’s hop count is more than the hop count limit, the packet is dropped. The 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 packet is less than the relay time

threshold, the packet will be dropped. The range is between 0 and 65,536 seconds, 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 default is Disabled.

DHCP Relay Hops

Count Limit (1-16)

This field allows an entry between 1 and 16 to define the maximum number of router 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 the 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 Switch will use

that value, along with the hop count to determine whether to forward a given DHCP 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 toggled to Enabled the relay agent will insert and remove

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 information, and the

IP address of the relay agent (if the relay agent is configured), to the packet. Once the

option 82 information has been added to the packet it is sent on to the DHCP server. When

the DHCP server receives the packet, if the server is capable of option 82, it can implement

policies like restricting the number of IP addresses that can be assigned to a single remote

ID or circuit ID. Then the DHCP server echoes the option 82 field in the DHCP reply. 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 the packet to the

switch port that connects to the DHCP client that sent the DHCP request.

Disabled – If the field is toggled to Disabled the relay agent will not insert and remove

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D-Link DGS-3700 User Manual Page 34

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D-Link DGS-3700 User Manual Page 34

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