Soekris can netboot via PXE. However, the default pxeboot file assumes a graphical console. NetBSD 3.0 provides an alternate image file to use serial console.

pxeboot_ia32_com0.bin was removed from NetBSD 4.0. The NetBSD 3.0 version is available here. It can be used to netboot NetBSD 4.0 (and probably current, but untested as of this writing).

There is an undocumented proceedure to change the boot options. This involves the use of dd(1) to change the configuration section thats a few pages into the start of the binary. I'll put up those instructions here if I ever get around to having to modify it.

(And these files really all shoulde be available under the installation subdir via official ftp, but they aren't.)