How to mount nfs folder from Debian on CentOS if it says “mount.nfs: No such device”?

Question

Debian

There are two servers: CentOS 6.7 and Debian 8.2. Between them in both directions I'm trying to make shared folders via NFS. The folder on CentOS (10.129.1.2) mounted nicely on Debian (10.129.1.3). But it doesn’t work in the opposite direction - share the Debian folder and mount it on CentOS.
Created a folder, added it to /etc/exports:

/var/nfstest    10.129.3.2(rw,sync,no_subtree_check)

With CentOS, you can even see it:

# showmount -e 10.129.1.3
Export list for 10.129.1.3:
/var/nfstest 10.129.3.2

But attempts to mount mount -vvv 10.129.1.3:/var/nfstest /mnt/nfs/nfstest/ fail:

mount: fstab path: "/etc/fstab"
mount: mtab path:  "/etc/mtab"
mount: lock path:  "/etc/mtab~"
mount: temp path:  "/etc/mtab.tmp"
mount: UID:        0
mount: eUID:       0
mount: no type was given - I'll assume nfs because of the colon
mount: spec:  "10.129.1.3:/var/nfstest"
mount: node:  "/mnt/nfs/nfstest/"
mount: types: "nfs"
mount: opts:  "(null)"
final mount options: '(null)'
mount: external mount: argv[0] = "/sbin/mount.nfs"
mount: external mount: argv[1] = "10.129.1.3:/var/nfstest"
mount: external mount: argv[2] = "/mnt/nfs/nfstest/"
mount: external mount: argv[3] = "-v"
mount: external mount: argv[4] = "-o"
mount: external mount: argv[5] = "rw"
mount.nfs: timeout set for Sun Apr 10 06:58:43 2016
mount.nfs: trying text-based options 'vers=4,addr=10.129.1.3,clientaddr=10.129.3.2'
mount.nfs: mount(2): No such device
mount.nfs: No such device

CHADNT and how to be?
Upd. the issue was resolved by replacing kernel with the version that had modules in /etc/modules Replacing kernel with DigitalOcean is done through the web control panel menu.

Answer 1

You don't seem to have a kernel module loaded. Do
lsmod | grep nfs
and, if the command shows nothing,
modprobe nfs