Why can't multiple devices connect to the VPN from the same network?

Question

linux

After trying several instructions, I finally got IPSec over L2TP VPN up on Ubuntu 14.04. Connects, works, but ran into one problem.
When connecting several devices from the same network behind NAT (and maybe several NATs), only the first one can connect. Unfortunately, I'm not well versed in networks and VPNs, so I'm asking for help.
What could be the problem?
/etc/ipsec.conf:

version 2.0
config setup
    dumpdir=/var/run/pluto/
    nat_traversal=yes
    virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v6:fd00::/8,%v6:fe80::/10
    protostack=netkey
    force_keepalive=yes
    keep_alive=60
conn L2TP-PSK-noNAT
    authby=secret
    pfs=no
    auto=add
    keyingtries=3
    ikelifetime=8h
    keylife=1h
    ike=aes256-sha1,aes128-sha1,3des-sha1
    phase2alg=aes256-sha1,aes128-sha1,3des-sha1
    type=transport
    left=0.0.0.0
    leftprotoport=17/1701
    right=%any
    rightprotoport=17/%any
    dpddelay=10
    dpdtimeout=20
    dpdaction=clear

/etc/xl2tpd/xl2tpd.conf

[global]
ipsec saref = yes
saref refinfo = 30

[lns default]
ip range = 192.168.1.1-192.168.1.128
local ip = 192.168.1.254
require authentication = yes
refuse pap = yes
pppoptfile = /etc/ppp/options.xl2tpd
length bit = yes

/etc/ppp/options.xl2tpd

require-mschap-v2
ms-dns 8.8.8.8
ms-dns 8.8.4.4
auth
mtu 1200
mru 1000
crtscts
hide-password
modem
name l2tpd
proxyarp
lcp-echo-interval 30
lcp-echo-failure 4

There are several users in /etc/ppp/chap-secrets. Each device connects under its own user.
It all works on a bunch of openswan + xl2tpd + ppp.

Answer 1

ip_conntrack_pptp и ip_nat_pptploaded?