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DES-3200-10/18/28/28F Layer 2 Ethernet Managed Switch User Manual
DHCP Relay
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 equal to or 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 BOOTREQUEST 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 65,535 seconds, with a
default value of 0 seconds.
DHCP Relay Global Settings
To enable and configure DHCP Relay Global Settings on the Switch, click Configuration > DHCP Relay > DHCP
Relay Global Settings:
Figure 2 - 15. 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 BOOTP or 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
BOOTP or DHCP packet.
DHCP Relay Agent
Information 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 DHCP
relay information (option 82 field) in messages between DHCP servers and clients, and the
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