Hi, and welcome
If you look at the pkg desciption via pacman
# pacman -Qi boot@ -66serv
it lists some optional dependencies:
Optional Deps : iptables: iptables support [installed]
nftables: nftables support
ebtables: ebtables support
arptables: arptables support
dmraid: dmraid support
lvm2: lvm support [installed]
btrfs-progs: btrfs support
zfs: zfs support
cryptsetup: encryption support
So when you use the comman 66-env to configure your boot module down the list, there is an option MNT_NETFS
If you say yes you must have the corresponding software, I believe it is included in libnfs or subnetds, it is not clear to me because
I don't have any ms fs to mount and try, so I always configure to =No I don't know whetehr nfstables is for MNT_NETFS or for mounting iptables.
I had asked that the dependencies for these be more clearly listed, either in the module configuration template, or the package's optional dependencies.
How to configure the boot module is in the wiki, on the intro and on boot-module entries.
If you don't configure one with a manual installation, just naming one and enabling it should get you booted (defaults pretty much lead to a universal boot). The beauty of 66 and modules is that you can configure it just the way you like it, lean, complicated, it is up to you.
ie. swap=no gets a system booted even if you have swap defined in /etc/fstab. It will not be used unless you change it to yes and pass the change to the boot tree (66-enable -t boot -F boot@ system). The reverse though, saying yes and not defining a valid swap (file or partition) in fstab will lead to a boot failure. When this happens you switch to tty12 (Ctl-Shft-F12) and log in as user and fix it.
With an installation done through obarun-install a default boot module named boot@ system is already set up for you.
I know it may sound complicated at first, but once you play with it for a few days you can hardly imagine a more controllable and configurable service/module management system.
Keep asking, when ever you feel you are lost. Do read some of the documentation listed on the link (top right "software") and the wiki, but more questions help improve the documentation.