xStack DES-3500 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual
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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 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.
DHCP / BOOTP Relay Global Settings
To enable and configure
DHCP/BOOTP Relay Global Settings
on the Switch, click
Configuration
>
Layer 3 Networking >
DHCP/BOOTP Relay
>
DHCP/BOOTP Relay Global Settings
:
Figure 6- 107. 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
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 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 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
check and policy settings will have no effect.
