This article explains an issue where SRX interface stops providing the DHCP service after the configuration change from MIST UI.

When DHCP service is enabled on any SRX interface from the MIST UI, it starts providing the IP addresses to DHCP clients without having the users to explicitly enable the DHCP service in the host inbound traffic. If the user tries adding any specific host inbound services like PING or TRACEROUTE except DHCP on that interface explicitly, DHCP will not work anymore.

This is an expected behaviour. When the user enables DHCP on any of the SRX interfaces via MIST, it will allow the DHCP host inbound service on the security zone level of which that interface is a part and when the user adds any specific host inbound service like Ping/traceroute on that specific interface, SRX will give preference to interface level configuration over the zone level configuration and in the interface level configuration user might have allowed all other inbound host services except DHCP.

Users need to explicitly allow the DHCP service as well in the interface level host inbound service configuration for the DHCP to continue working, as given below:

User@SRX#set security zones security-zone Test interface irb.20 host-inbound-traffic system-services dhcp