Junos OS

Hi Everyone,
I am currently trying to setup a pxe boot. So far I have setup when we pxeboot our dell server it does successfully grab an IP address, but then failed with error "PXE-E11: ARP timeout"

My dhcp helper configuration look as this:
{master:0}[edit routing-instances users forwarding-options]
lpaulin@4dc-core-01# show | display inheritance no-comments
dhcp-relay {
overrides {
always-write-giaddr;
}
server-group {
KRK-COBBLER {
10.X.51.10;
}
}
group PXEBOOT {
active-server-group KRK-COBBLER;
overrides {
delete-binding-on-renegotiation;
}
relay-option {
option-number 60;
equals {
ascii PXEClient {
forward-only;
}
}
}
interface irb.2051;
}
}

I have also try to enable to tftp helpper but does not seem to work either...
lpaulin@4dc-core-01# show | display inheritance no-comments
helpers {
tftp {
server 10.X.51.10;
interface {
irb.2051;
}
}
}

Am I missing something in the configuration? My switches are 2 QFX10K in Junos Fusion Datacenter topology.

Do you need the options?
I have working PXE with the following, does DHCP and PXE, only goes to the PXE server for PXE stuff.

dhcp-relay {
overrides {
delete-binding-on-renegotiation;
}
server-group {
DHCP-WITH-PXE {
10.x.x.22; ---DHCP Server
10.x.x.23; ---DHCP Server
10.x.x.41;----PXE Server
10.x.x.21; ----PXE Server
}
}
group DHCP-CLIENT-PXE {
active-server-group DHCP-WITH-PXE;
interface irb.1001;
interface irb.1111;
interface irb.2661;
}
}

Thanx @agarrison, 

Already try a configuration similar like your and got the same result.  

What I acutually found lately is that if I run continuous ping to the IP the server grab, once pxe say it acquire the IP the router can't ping it at al, even though that I can see it's mac address within the switching table. Also if boot the server within the OS, I can ping the host successfully. So this lead me to thing that either there's a issue with the pxe client or the switches does let pass pxe/tftp traffic properly.  

Any thoughs about this ?  I am about to open a case with Juniper, though that I not convice if it's an issue with switches configuration or something else.