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+In order to boot OPNSense via iPXE,
+you need to do the following:
+
+1. Download ISO from http://opnsense.mirrorhost.pw/releases/17.7/OPNsense-17.7-OpenSSL-serial-amd64.img.bz2
+
+   Optionally, you can verify signature of the file, to make sure
+   it wasn't tampered:
+   https://opnsense.org/opnsense-17-7-released/
+   
+   You should also check the SHA256 hash:
+   `sha256 -c bc8b529accab5609aafaac04504cae48cbb69eb2320b72eadb9c3a1f1b0d4832 OPNsense-17.7-OpenSSL-serial-amd64.img.bz2`
+   and compare it to the one in http://opnsense.mirrorhost.pw/releases/17.7/OPNsense-17.7-OpenSSL-checksums-amd64.sha256
+
+2. Extract the ISO contents to a directory called
+    `images/opsense` in TFTP root:
+    `bzip2 -d OPNsense-17.7-OpenSSL-serial-amd64.img.bz2`
+    
+   In order to extract the contents, you need to mount
+   the ISO with following commands (example from FreeBSD):
+   `mount /dev/$(mdconfig -a -t vnode -f OPNsense-17.7-OpenSSL-serial-amd64.img)a /mnt`
+   
+   To mount the ISO from GNU / Linux use:
+   `mount -o loop pfSense-CE-2.3.4-RELEASE-amd64.iso /mnt`
+
+   Then:
+   `rsync -avvP /mnt/ /srv/tftp/images/opnsense/`
+   You need to have `rsync` installed.
+
+2. Relevant entry in DHCP server config:
+    `option root-path /srv/tftp/images/opnsense;`
+   `/srv/tftp/images/opnsense` is the path to the extracted ISO.
+
+3. Relevant entries in PXELINUX config:
+```
+label OPNSense
+ menu label OPNSense
+ pxe images/opnsense/boot/pxeboot
+```
+
+The path `images/pfsense/boot/OPNSense` is relative to TFTP root directory.
+It's a path to the PXE loader in the extracted OPNSense installation image.
+
+Unfortunately, there's no mechanism for unattended installation of OPNSense:
+https://github.com/opnsense/core/issues/18