Where doe PXWWorx get "transaction server"

Question

We are trying to reconfigure our network so that ZenWorks boot clients get their initial DHCP information from the local router rather than using DHCP relay..
When I try to boot a client, I can successfully load dinic.sys via TFTP on the "distant" Zen imaging server, apparently based on the initial DHCP parameter "next -server". So the host is getting an IP address, route, and the address of the TFTP server. This setup also works to successfully boot generic Linux with PXElinux.
But with Zenworks, after it loads dinic.sys it doesn't know how to contact the Zen imaging server via UDP port 4011, the next step in the boot process:
DHCP (succeeds)
PreWorx Pty Ltd
Issuing New DHCP Request
Local IP: 10.3.1.100
Subnet Mask: 255.255.255.0
Transaction Server ID: 0.0.0.0
Error! No Response from port map service
Zenworks shutting down.
So - what DHCP parameter / option is used to communicate the "Transaction Server" to the booting client? It's NOT "next-server" or "boot-server" as far as I can tell.
Thanks,
-Wiley Sanders
System Administrator
St Marys College of Calfornia

Answer 1

This turns out to be supplied by the undocumented DHCP Options 180, 181, and 182. We added the Zen Imaging server IP to Options 180 and 181, and added 0.0.0.0 to Option 182 and this seems to allow our PCs to boot off a "remote" Zen Imaging server on another subnet, using the router as the initial DHCP server on the local subnet. We arrived at this fix after snooping the booting process with Wireshark.
For those of you fortunate enough to be running JunOS, the configuration is as follows:
{master:0}[edit system services dhcp]
wms2@ccf4200stack# show
domain-name mydomain.edu;
name-server {
[etc]
wins-server {
[etc]
boot-file dinic.sys;
next-server 10.0.1.99;
option 180 ip-address 10.0.1.99;
option 181 ip-address 10.0.1.99;
option 182 ip-address 0.0.0.0;
pool 10.3.0.0/24 {
address-range low 10.3.0.100 high 10.3.0.249;
router {
10.3.0.254;
[etc]
Where 10.0.1.99 is the address of the Zen Image server.