This article explains a scenario where the QFX5100 acting as a DHCP relay device is not forwarding DHCP packets from the client to the server. The client is not receiving any DHCP IP.

Lab Setup and how to repeat:

>> Configure QFX5100 with "set forwarding-options helpers port 1234 server 30.30.30.1"

IXIA --------QFX5100--------Switch

>> Send traffic to QFX5100 from IXIA with source/Dest IP as 1.1.1.10 and 2555.255.255.255 and UDP source/dest port as 1234. Add DHCP as payload

>> Check "monitor interface traffic" and QFX5100 is not forwarding the packets.

lab@qfx5100> show configuration forwarding-options | display set

set forwarding-options helpers port 1234 server 30.30.30.1

Interface Link Input packets (pps) Output packets (pps)

xe-0/1/1 Up 106241 (0) 157653 (0) <<<<<<<<<<<<<<<<<<<<< OUT is zero

xe-0/1/2 Up 7978978 (1000) 2307 (0) <<<<<<<<<<<<<<<<<<<<< IN but not forwarding

The Knob "set forwarding-options helpers port <> server <>" is not supported in QFX5100 on any release. You would need to use DHCP relay feature for forwarding DHCP packets on QFX5100. Please use the below documentation to configure the device as a DHCP relay-agent.
 

Sample configuration for DHCP relay agent:

set forwarding-options dhcp-relay forward-only 
set forwarding-options dhcp-relay relay-option-82 circuit-id use-interface-description devices
set forwarding-options dhcp-relay server-group my-dhcp-servers-group 30.30.30.1
set forwarding-options dhcp-relay active-server-group my-dhcp-servers-group
set forwarding-options dhcp-relay group my-dhcp-interf-group interface xe-0/1/1.0
set forwarding-options dhcp-relay group my-dhcp-interf-group interface xe-0/1/2.0
 

https://www.juniper.net/documentation/us/en/software/junos/dhcp/topics/topic-map/dhcp-relay-agent-security-devices.html