The IPSec documentation may contain a bug.

    https://www.freebsd.org/doc/handbook/ipsec.html

In particular, the command is given as:

    # ifconfig gif0 internal1 internal2

and then the resulting gif0 interface looks like

    inet 10.246.38.1 --> 10.0.0.5 netmask 0xffffff00

It would appear that the mask is missing from the command like so:

    # ifconfig gif0 internal1 netmask 255.255.255.0 internal2


Even better, since example IP addresses are used in these docs, write it like this:


    # ifconfig gif0 10.246.38.1 netmask 255.255.255.0 10.0.0.5

and it will be much clearer as to which IP address you are supposed to put where. The documentation never explains which end of the link is supposed to be internal1 and which is internal2. At the very least, rename them as external_remote and external_local.