D-Link xStack DGS-3426P User Manual - Dhcp/bootp Relay

xStack DGS-3400 Series Layer 2 Gigabit Ethernet Managed Switch 

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 Administration > DHCP/BOOTP Relay > 

DHCP/BOOTP Relay Global Settings: 

Figure 6- 44.  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 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. 

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