DHCP bootp helper not forwarding on EX2200

Hi,

We have an EX2200 which we are configuring to be compatible with a PXE boot system. We've got it working on our Brocade switches but Juniper is proving more difficult.

• "show helper statistics" shows 0 packets 
• the DHCP server is 3 hops away, but can be pinged from vlan.323
• traceoption logs show absolutely nothing
• IPs have been partially redacted 
• have tested with and without both the "relay-agent-option" and "broadcast" bootp settings.
• the server on v316 is definitely sending out a DHCP request. 

Can anyone shed some light on this? I'm totally stumped. 

# show interfaces ge-0/0/27 
unit 0 {
    family ethernet-switching {
        port-mode access;
        vlan {
            members v316;
        }
    }
}

# show vlans v316 
vlan-id 316;
interface {
    ge-0/0/27.0;
}
l3-interface vlan.323;

> show configuration interfaces vlan unit 323     
family inet {
    address 11.111.162.169/29;
}

# show forwarding-options 
helpers {
    traceoptions {
        file helper;
        level all;
        flag bootp;
    }
    bootp {
        relay-agent-option;
        server 11.111.162.15;
        maximum-hop-count 10;
        interface {
            vlan.323 {
                server 11.111.162.15;
                maximum-hop-count 10;
            }
        }
    }
}

> show helper statistics 
BOOTP:
  Received packets: 0
  Forwarded packets: 0
  Dropped packets: 0
    Due to no interface in DHCP Relay database: 0
    Due to no matching routing instance: 0
    Due to an error during packet read: 0
    Due to an error during packet send: 0
    Due to invalid server address: 0
    Due to no valid local address: 0
    Due to no route to server/client: 0> show log helper 

{master:0}

> ping 11.111.162.15 source 11.111.162.169 
PING 11.111.162.15 (11.111.162.15): 56 data bytes
64 bytes from 11.111.162.15: icmp_seq=0 ttl=62 time=8.123 ms
64 bytes from 11.111.162.15: icmp_seq=1 ttl=62 time=3.237 ms