@Rosko I am still quite confused about this post and all the ref links within. What's the final words on this? We are purchasing a fleet of new iMacs and I am hoping to NetBoot them to image as the first thing powering up.
Which approach should I take? We are running multi-VLAN and Option + N won't Netboot the device. In the past, I ran Bless command after logging into the new iMac to Netboot by specify the NetBoot Server and Image (very long command). When do I add this extra process (or command) of trusting the NetBoot Server?
Thanks for all help!

@wangl2, to hopefully help clarify the issue, please see the graphic below.

Thanks Rich!
We do use Bless command to NetBoot iMacs. So where about do we fit in this extra command to trust the NetBoot server?
Regards,

I'm not sure what is the issue discussed here. I haven't run into this.

When we receive a new Mac, we just NetBoot it, image it, and go. All the ones we got this year have all had El Capitan factory-installed, and I've been able to NetBoot, and re-image all of them without any problems.

Is this an issue when adding a NetBoot server to JSS? We don't do that here.

@wangl2 You cannot automate it.

You'll need to boot into recovery & add the IP via csrutil, then NetBoot.

But.. the values you add via csrutil are wiped when PRAM reset.

The proper fix is IPHelpers.

@itupshot it's only an issue of NetBoot Server is not on the same Vlan as the Macs & no IPHelper in place.

@bentoms Thanks dude. You must remembered my old post.
Yes we always had problem with NetBoot and every time there is a new release of OS X, I have to alter the command. Maybe I have been been doing the wrong way that's why I am always hoping someone can direct me to the right path. We run multi VLAN and cannot simple NetBoot it by holding Option + N. We run quite a complex Bless command to boot new iMacs, which not only specify the IP of the NetBoot Server, but also the path to the right NBI files. So we prepare the NetBoot image on the NetBoot server to create a NBI by using System Image Utility. Then run the Bless command on the new iMacs, which we have to turn it on, go through the activation thing and create a local account. To keep the NetBoot image consistent with the newer iMacs, the image size just grows bigger and bigger. Usually I just take a snapshot of the factory image and add Casper Suite, use that as a minimal image to create my NetBoot Image using SIU. I just did one for 10.11 and the size has grown to over 15GB.
I don't like this process at all. So anyone have better ideas of doing this, please let me know.
Thanks all