Weird Netbooting issue

Update;
when I run the bless command the machine does not net boot sudo bless --netboot --nextonly --server bsdp://10.xx.xxx.xx

Have you tried pinging your netbook server from all three machines and checked the current IP addresses are valid on the machines? Could your Macbook be on an old IP address? If not then it is possibly a physical fault or a faulty switch?

@SimonCU That is the weird part. I can ping from all of the effected machines. Its driving me nuts. Considering building a "secret os x server" on my laptop and bringing in a switch to get the job done

@CapU are you running 10.11.3 on the Laptop? There was a bug with seeing things in the startup disk pref pane with that & thunderbolt adaptors, updating OSX should resolve.

Other things:

1) are the clients running 10.11?

2) Do you have IPHelpers in place or are the clients on the same lan as the server?

3) if you option boot, can you see the server?

@bentoms 1: Im running 10.11.2 on my laptop. Not really a big deal if I can't netboot
2: IP helpers are in place. The 2nd floor is on the same vlan and those machines can see the .nbi and netboot
3: I can't see the server if I option boot

@CapU juat update the OS on your laptop £ that should be working.

If you have any other 10.11.2 MBP's, update them too.

I couldn't wait for the networking guys (It may not be a networking issue I fear, or a Casper issue) I was able to successfully image the lab using Casper Imaging on my laptop then went back to my desk to finish them off.
Luckily there were only 14 in total.

Not sure what OS version your netboot server is on but just an FYI, Ever since we've upgraded our netboot server to El Capitan 10.11, we've experienced a whole lot of issues with net booting/network related issues. I would say if your on El Cap, setup another machine with Yosemite and configure your Server app on that OS.