I have a question about how the SRX processes DHCP relay packets. I have a remote site with a Cisco switch trunked to an SRX which is connected to my DHCP server via a tunnel. The host DHCP requests are handled by the helper IPs on the Cisco. When I took over this network, the hosts were not able to get an IP via DHCP. After looking at the SRX config I noticed the irb interface was not included in the relay group. I added it and now the hosts are able to receive an IP from the server. My question is why does the interface on the SRX need to be in the relay group if the Cisco is handling the DHCP requests? Is it because it's seeing the unicast traffic on port 67 on the irb and knows that it is DHCP relay traffic and it won't process it unless the interface is in the relay group?
Thanks for any information on this.