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Why are some of the DHCP requests not forwarded?

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TitleWhy are some of the DHCP requests not forwarded?
This article discusses why DHCP requests are not forwarded in the subnet which also has the default route to the DHCP server.

By default when DHCP helper-address is configured under a VLAN, the router forwards the DHCP broadcast requests from clients on one subnet to the DHCP server on another subnet as a unicast. However the DHCP requests are not forwarded when the route to the DHCP server is also on the same subnet. Thisis because both the incoming and outgoing interfaces for Client and server are on the same subnet.

Below is the Sample N/W Diagram and Relevant Configuration:
Note:Port 2/5 (DHCP Client) and Porte 1/24 (Outgoing port to the DHCP Server) are in the same subnet and VLAN (10).

MLXe-4-(1/24)-----------(2)RTR-A-----RTR-B---------DHCP Server (

DHCP Client


vlan10 nameTest
untagged ethe 1/24 ethe 2/5
router-interface ve 10
ip route

interface ve 10
ip address
ip helper-address

In this case,enablingthe unicast option of the helper-address will force the router to forward the DHCP requests on this subnet to the DHCP server on a different subnet as Unicast.

ip helper-address unicast

Additional notes



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