If you wish to distribute NetworkManager-l2tp 1.8.0 binaries for a Linux distribution, please note that there is a GPL/OpenSSL license conflict with OpenSSL < 3.0.0 on Linux distibutions that do not consider OpenSSL (or LibreSSL) to be a "System Library". See release notes for further details:
NetworkManager-l2tp is a VPN plugin for NetworkManager 1.8 and later which provides support for L2TP and L2TP/IPsec (i.e. L2TP over IPsec) connections.
For L2TP support, it uses xl2tpd ( https://www.xelerance.com/software/xl2tpd/ )
For IPsec support, it uses either of the following :
- Libreswan ( https://libreswan.org )
- strongSwan ( https://www.strongswan.org )
For user authentication it supports either:
- username/pasword credentials.
- TLS certificates.
For machine authentication is supports either:
- Pre-shared key (PSK).
- TLS certificates.
This VPN plugin auto detect the following TLS certificate and private key file formats by looking at the file contents and not the file extension :
- PKCS#12 certificates.
- X509 certificates (PEM or DER).
- PKCS#8 private keys (PEM or DER)
- traditional OpenSSL RSA, DSA and ECDSA private keys (PEM or DER).
For TLS user certificate support, the ppp package has to have the EAP-TLS patch for pppd applied to the ppp source code (which many Linux distributions already do) :
For details on pre-built packages, known issues and build dependencies, please visit the Wiki :
./autogen.sh
./configure # (see below)
make
The default ./configure settings aren't reasonable and should be explicitly
overridden with ./configure arguments. In the configure examples below, you
may need to change the --with-pppd-plugin-dir value to an appropriate
directory that exists.
./configure \
--disable-static --prefix=/usr \
--sysconfdir=/etc --libdir=/usr/lib/x86_64-linux-gnu \
--libexecdir=/usr/lib/NetworkManager \
--localstatedir=/var \
--with-pppd-plugin-dir=/usr/lib/pppd/2.4.7
./configure \
--disable-static --prefix=/usr \
--sysconfdir=/etc --libdir=/usr/lib64 \
--localstatedir=/var \
--with-pppd-plugin-dir=/usr/lib64/pppd/2.4.7
./configure \
--disable-static --prefix=/usr \
--sysconfdir=/etc --libdir=/usr/lib64 \
--libexecdir=/usr/lib \
--localstatedir=/var \
--with-pppd-plugin-dir=/usr/lib64/pppd/2.4.7
VPN connection profile files (along with other NetworkManager profile files)
are stored under /etc/NetworkManager/system-connections/
The following files located under /var/run assume --localstatedir=/var or
--runstatedir=/var/run were supplied to the configure script at build time.
- /var/run/nm-l2tp-UUID/xl2tpd.conf
- /var/run/nm-l2tp-UUID/xl2tpd-control
- /var/run/nm-l2tp-UUID/xl2tpd.pid
- /var/run/nm-l2tp-UUID/ppp-options
- /var/run/nm-l2tp-UUID/ipsec.conf
- /etc/ipsec.d/ipsec.nm-l2tp.secrets
where UUID is the NetworkManager UUID for the VPN connection.
If strongswan is being used, NetworkManager-l2tp will append the following line
to /etc/ipsec.secrets at run-time if the line is missing:
include ipsec.d/ipsec.nm-l2tp.secrets
By default the libreswan NSS database is created in /etc/ipsec.d/ and is used
by NetworkManager-l2tp for VPN connections using libreswan and machine
certificates.
The default libreswan package install for most Linux distributions uses an empty password. It is up to the administrator to decide on whether to use a password or not. However, a non-empty database password must be provided when running in FIPS mode.
See the following page on how to set the password for the libreswan NSS database
and the syntax for the /etc/ipsec.d/nsspassword file where the password is
stored:
For Systemd based Linux distributions logging goes to the Systemd journal which can be viewed by issuing the following :
journalctl --unit=NetworkManager
For non-Systemd based Linux distributions, view the appropriate system log
file which is most likely located under /var/log/.
To increase debugging output, issue the following on the command line, it will also prevent the run-time generated config files from being deleted after the VPN connection is disconnected :
sudo killall -TERM nm-l2tp-service
sudo /usr/lib/NetworkManager/nm-l2tp-service --debug
sudo killall -TERM nm-l2tp-service
sudo /usr/libexec/nm-l2tp-service --debug
sudo killall -TERM nm-l2tp-service
sudo /usr/lib/nm-l2tp-service --debug
then start your VPN connection and reproduce the problem.
For Systemd based Linux distributions when increasing the debugging output
by running nm-l2tp-service --debug on the command-line, do not use
journalctl --unit=NetworkManager as you may not see all the logs, instead
issue:
journalctl -b
The Libreswan debugging can be cutomized by setting the PLUTODEBUG env
variable which corresponds to the plutodebug ipsec.conf config section option.
The syntax for PLUTODEBUG is a white-space separated list of the following
format :
PLUTODEBUG="TYPE TYPE ... TYPE"
Where TYPE is a debug option from the list output by issuing the following on the command-line :
ipsec whack --debug list
Examples:
sudo PLUTODEBUG="all proposal-parser" /usr/lib/NetworkManager/nm-l2tp-service --debug
sudo PLUTODEBUG="all proposal-parser" /usr/libexec/nm-l2tp-service --debug
The strongSwan debugging can be cutomized by setting the CHARONDEBUG env
variable which corresponds to the charondebug ipsec.conf config section option.
The syntax for CHARONDEBUG is a comma separated list of the following format :
CHARONDEBUG="TYPE LEVEL, TYPE LEVEL, ..., TYPE LEVEL"
where TYPE is: any|dmn|mgr|ike|chd|job|cfg|knl|net|asn|enc|tnc|imc|imv|pts|tls|esp|lib
and LEVEL is: -1|0|1|2|3|4
Examples:
sudo CHARONDEBUG="knl 1, ike 2, esp 2, lib 1, cfg 3" /usr/lib/NetworkManager/nm-l2tp-service --debug
sudo CHARONDEBUG="knl 1, ike 2, esp 2, lib 1, cfg 3" /usr/libexec/nm-l2tp-service --debug
sudo CHARONDEBUG="knl 1, ike 2, esp 2, lib 1, cfg 3" /usr/lib/nm-l2tp-service --debug
NetworkManager-l2tp starts its own instance of xl2tpd and if the system xl2tpd service is running, its own xl2tpd instance will not be able to use UDP port 1701, so will use an ephemeral port (i.e. random high port).
Although the use of an ephemeral port is considered acceptable in RFC3193, the L2TP/IPsec standard co-authored by Microsoft and Cisco, there are some L2TP/IPsec servers and/or firewalls that will have issues if an ephemeral port is used.
Stopping the system xl2tpd service should free UDP port 1701 and on systemd based Linux distributions, the xl2tpd service can be stopped with the following:
sudo systemctl stop xl2tpd
If stopping the xl2tpd service fixes your VPN connection issue, you can disable the xl2tpd service from starting at boot time with :
sudo systemctl disable xl2tpd
There is a general consensus that the following legacy algorithms are now considered weak or broken in regards to security and should be phased out and replaced with stronger algorithms.
Encryption Algorithms :
- 3DES
- Blowfish
Integrity Algorithms :
- MD5
- SHA1
Diffie Hellman Groups :
- MODP768
- MODP1024
- MODP1536
The following strongSwan page has more details on which algorithms are considered broken:
Legacy algorithms that are considered weak or broken are regularly removed from the default set of allowed algorithms with newer releases of strongSwan and libreswan.
As of NetworkManager-l2tp version 1.2.16, it was decided to compromise for backwards compatibility by not using the strongSwan and libreswan default set of allowed algorithms, instead algorithms that are a merge of Windows 10 and macOS/iOS/iPadOS L2TP/IPsec clients' IKEv1 proposals are used instead. The weakest proposals that were not common to both Win10 and iOS were dropped, but all of the strongest ones were kept:
| Phase 1 - Main Mode |
|---|
| {enc=AES_CBC_256 integ=HMAC_SHA2_256_128 group=MODP_2048} |
| {enc=AES_CBC_256 integ=HMAC_SHA2_256_128 group=MODP_1536} |
| {enc=AES_CBC_256 integ=HMAC_SHA2_256_128 group=MODP_1024} |
| {enc=AES_CBC_256 integ=HMAC_SHA1_96 group=MODP_2048} |
| {enc=AES_CBC_256 integ=HMAC_SHA1_96 group=MODP_1536} |
| {enc=AES_CBC_256 integ=HMAC_SHA1_96 group=MODP_1024} |
| {enc=AES_CBC_256 integ=HMAC_SHA1_96 group=ECP_384} |
| {enc=AES_CBC_128 integ=HMAC_SHA1_96 group=MODP_1024} |
| {enc=AES_CBC_128 integ=HMAC_SHA1_96 group=ECP_256} |
| {enc=3DES_CBC integ=HMAC_SHA1_96 group=MODP_2048} |
| {enc=3DES_CBC integ=HMAC_SHA1_96 group=MODP_1024} |
| Phase 2 - Quick Mode |
|---|
| {enc=AES_CBC_256 integ=HMAC_SHA1_96} |
| {enc=AES_CBC_128 integ=HMAC_SHA1_96} |
| {enc=3DES_CBC integ=HMAC_SHA1_96} |
The above proposals are equivalent to setting the following phase 1 and 2 algorithms in the Advanced section of NetworkManager-l2tp's IPsec Options dialog box:
Phase 1 algorithms with libreswan :
aes256-sha2_256-modp2048,aes256-sha2_256-modp1536,aes256-sha2_256-modp1024,aes256-sha1-modp2048,aes256-sha1-modp1536,aes256-sha1-modp1024,aes256-sha1-ecp_384,aes128-sha1-modp1024,aes128-sha1-ecp_256,3des-sha1-modp2048,3des-sha1-modp1024
Phase 2 algorithms with libreswan :
aes256-sha1,aes128-sha1,3des-sha1
Phase 1 algorithms with strongSwan :
aes256-sha2_256-modp2048,aes256-sha2_256-modp1536,aes256-sha2_256-modp1024,aes256-sha1-modp2048,aes256-sha1-modp1536,aes256-sha1-modp1024,aes256-sha1-ecp384,aes128-sha1-modp1024,aes128-sha1-ecp256,3des-sha1-modp2048,3des-sha1-modp1024!
Phase 2 algorithms with strongSwan :
aes256-sha1,aes128-sha1,3des-sha1!
If you are not sure if you are using libreswan or strongSwan, issue the following on the command-line:
ipsec --version
If you are concerned about security and wish to use algorithms that are
stronger than the proposals offered by Windows 10 and macOS/iOS/iPadOS
L2TP/IPsec clients, user specified phase 1 (ike - Main Mode) and phase 2
(esp - Quick Mode) algorithms can be specified in the IPsec Options dialog
box. Please see the libreswan or strongSwan ipsec.conf documentation for the
ike and esp (aka phase2alg) syntax.
If you are not sure which IKEv1 Phase 1 algorithms your VPN server proposes,
you can query the VPN server with the ike-scan.sh script located in the
IPsec IKEv1 algorithms section of the Wiki :