@Cookie_050 Great Idea, I tried it with my setup, but it does not work in my case, unfortunately.

Although option 66 is empty, the client still tries to pull from x.0.1 instead of x.0.5. Have a look:

I even bought a new ER605 because I owned an old hardware version, but even with the latest firmware, no success in booting from the network.

For everyone else trying this, please let me know if this helped you, maybe we find other ways to cheat around the not working option 66.

  @Cookie_050 Yes it has. I can pull it manually but from the x.0.5 IP.
As you can see on the image, this client does pull from x.0.1, which is the ER605.

Option 66 was not provided during this try.
If I set the x.0.5 in the Option 66 on my Cntroller, the behavior is exactly the same.

  @Cookie_050 Yes, you are partly correct. The next server option isn't used, since it uses the Gateway. But Even if option 66 is configured it does this.
Here is an example that the tftp is fine:

So in a nutshell:
If 66 is configured: It doesn't work because the option isn't working and the client uses the gateway.

If 66 is not configured and in 67 the "cheat" path with "tftp://..." is set, the client ignores the path and only searches for the file "tftp://..." on gateway IP.

That's what Iam getting.

Best