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xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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DHCP/BOOTP Relay
The relay hops count limit allows the maximum number of hops (routers) that the DHCP/BOOTP 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 BOOTREQUEST packet. If the value in the second’s 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.
DHCP / BOOTP Relay Global Settings
To enable and configure DHCP/BOOTP Relay Global Settings on the Switch, click L3 Features > DHCP/BOOTP Relay >
DHCP/BOOTP Relay Global Settings:
Figure 8- 51. DHCP/ BOOTP Relay Global Settings window
The following fields can be set:
Parameter Description
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/BOOTP Relay service on the Switch. The default is
Disabled. If the DHCP server is enabled, DHCP relay can not be enabled. The opposite is
also true.
Relay Hops Count
Limit (1-16)
This field allows an entry between 1 and 16 to define the maximum number of router hops
DHCP/BOOTP messages can be forwarded across. The default hop count is 4.
Relay Time Threshold
(0-65535)
Allows an entry between 0 and 65535 seconds, and defines the maximum time limit for
routing a DHCP/BOOTP packet. If a value of 0 is entered, the Switch will not process the
value in the second’s 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 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