Netboot - Weird and Inconsistant Netboot behavior

[NLSD69]

Hello, I have been using netboot/netinstall for about 7 years now, on the Classic Server OS, and also the new incarnation of the server app, running on servers with an OS as new as El Capitain. We manage 31 school sites, and many of them have Netboot functioning with no issues...that being said, as long as I followed the basic rules, I've had incredible luck with it...until recently. My high school side, suffers from the following:

• Slow netboot
• Inconsistent netboot, IE: sometimes it works, sometimes it dosen't...at all..sometimes it loads half way...but as of late, I can barely get one Mac to boot from netboot at all, if at all....
• However, here's the weird part, in general, the network "seems" healthy. Good download speed, when netboot does work, the computers image at a reasonable pace, for the image size, and I can do several at once no problem...it just seems the issue is getting netboot function consistantly on this site...

If I were to fire up wireshark to look for issues, can anyone give me some suggestions, of what kind of traffic to look for or behavior that would negatively effect netboot? Is there any praticular network protocol, or culprit that people have identified, that absolutely kills netboot traffic? In my case it seems like something is impedining its behavior, or there may be a load of a certain kind of traffic that is not effecting daily use, but seems to be effecting netboot. Outside of spanning tree protocol, anything else on a swtich that would affect netboot?

Thanks in advance. Any help is much appreciated.

[MAD0oM]

Couple Things @NLSD69 Do you have firewall anywhere? Any changes in network switches?

Slow netboot: Could be cause of firewall/ Network changes (switch changes etc )

Inconsistent netboot, IE: sometimes it works, sometimes it dosen't...at all..sometimes it loads half way...but as of late, I can barely get one Mac to boot from netboot at all, if at all: Few things with this one.. DHCP server needs to respond to assign the machine an IP address and then your Netboot images boot file is downloaded once the machine has one. i'd check to see if your Netboot server and clients are on the same subnet and if you're not booting on same subnet then adding your netboot server's IP to your DHCP relay in your routers config.

However, here's the weird part, in general, the network "seems" healthy. Good download speed, when netboot does work, the computers image at a reasonable pace, for the image size, and I can do several at once no problem...it just seems the issue is getting netboot function consistantly on this site:

How did you check your network health? i'd check to see if you're on the same subnet again, Also you can do a packet trace using tcpdump Usually it could mean a bunch of things but i'd start with the items i've pointed out also

Some more info would be great to help out some more