Re: DHCP exclude-address on QFX5100

I would guess that this function hasn't been implemented on DHCPD on QFX. You need to use JDHCPD instead which is the way to go moving forward.

Here is a configuration example for JDHCPD-style configuration: https://www.juniper.net/documentation/en_US/junos16.1/topics/task/configuration/dhcp-server-cli-els.html

You can then configure an excluded address via something like this:

set access address-assignment pool XXX family inet excluded-address 10.253.12.45

Please note: You have to remove all existing DHCPD configuration to change to JDHCPD as these cannot run at the same time.

Hope this helps.