Windows 7 and newer releases support IKEv2 and MOBIKE (RFC 4555) through Microsoft’s Agile VPN functionality and are therefore able to interoperate with a strongSwan VPN gateway using these protocols. The Windows client does not currently support IKE redirection (RFC 5685) and multiple authentication rounds (RFC 4739).
By default Windows 7 up to Windows 11 propose only the weak
Diffie-Hellman key exchange algorithm that has been deprecated by
NIST Special Publication 800-57 Part 3 Revision 1 since 2015:
ike = 3des-aes128-aes192-aes256-sha1-sha256-sha384-modp1024
Additionally Windows 11 proposes the
AES-GCM authenticated encryption algorithm
(AEAD) but unfortunately with the weak
modp1024 DH group, too.
ike = aes128gcm16-aes256gcm16-sha1-sha256-sha384-modp1024
So if you don’t want any major secret service to eavesdrop on your communication
we strongly urge you to enable the
modp2048 Diffie-Hellman group by adding the
DWORD in the windows registry using
The values that can be used are
2. The table below tells you
what the values mean.
Disable AES-256-CBC and MODP-2048. This is the default
Enable AES-256-CBC and MODP-2048
Enforce the usage of AES-256-CBC and MODP-2048
With the value set to
2, Windows 11 proposes
ike = aes256-sha1-sha256-sha384-modp2048
Unfortunately the ESP proposals still contain the weak single
DES and even
NULL encryption algorithms and data integrity is restricted to
esp = aes256-aes128-3des-des-null-sha1
strongSwan currently can authenticate Windows clients either on the basis of
The strongSwan VPN gateway and each Windows VPN client needs an X.509 certificate
issued by a Certification Authority (CA). OpenSSL or the
pki tool can be used to generate these certificates, see
our Quickstart tutorial. Make sure to fulfill the
certificate requirements, so that Windows
VPN clients and strongSwan VPN gateways can mutually authenticate themselves
Certificates are stored in a user-specific keystore and it’s also possible to
use smart cards. The client authentication has to be done with
EAP-TLS on top of
In order to prevent man-in-the-middle attacks the strongSwan VPN gateway always
authenticates itself with an X.509 certificate using a strong RSA/ECDSA signature.
After a secure communication channel has been set up by the IKEv2 protocol, the
Windows clients authenticate themselves using the
EAP-MSCHAPv2 protocol based
on user name, optional windows domain and user password. As an EAP identity
exchange is needed for this to work, make sure to have the
EAP-MSCHAPv2 requires MD4 to generate the NT-Hashes, so either the
or one of the crypto library plugins (
gcrypt) is required. This
is not needed if the authentication is delegated to an AAA server via
Some Windows clients will always send a domain part in the user name field (e.g.
Windows Phone\User). Depending on the backend used to authenticate the users,
the domain part may have to be stripped away or be included when defining the
credentials (e.g. in the
secrets section of
The Windows client supports IKE_SA rekeying but can’t handle unsupported Diffie
Hellman groups. If a strongSwan gateway initiates an IKE_SA rekeying, it must use
modp2048 as the DH group in the first attempt, otherwise rekeying fails.
You can achieve this by setting
modp2048 as the first (or only) DH group in
ike proposal of the VPN gateway.
Rekeying CHILD_SAs is also supported by the Windows client. For some reason, a
client behind NAT does not accept a rekeying attempt and rejects it with a
Microsoft specific notify
12345 containing an error code
To work around the issue, let the client initiate the rekeying by setting
connections.<conn>.children.<child>.rekey_time = 0
on the strongSwan VPN gateway.
IKEv2 fragmentation is supported since the v1803 release of Windows 10 and Windows Server. All versions of Windows also support the proprietary IKEv1 fragmentation.
Microsoft changed the Windows 10 VPN routing behavior for new VPN connections.
Option "Use default gateway on remote network option" in the Advanced TCP/IP settings
of the VPN connection is now disabled by default but can be enabled if desired.
Fortunately Windows sends a DHCP request upon connection and add routes supplied
249 of the DHCP reply.
Sample configuration file for dnsmasq:
dhcp-vendorclass=set:msipsec,MSFT 5.0 dhcp-range=tag:msipsec,192.168.103.0,static dhcp-option=tag:msipsec,6 dhcp-option=tag:msipsec,249, 0.0.0.0/1,0.0.0.0, 18.104.22.168/1,0.0.0.0
192.168.103.0 is your (internal) network. It pushes two separate routes
which cover the entire IPv4 range. Gateway could be anything (set to
in an example) as it is ignored by Windows. Note that you can’t ignore DHCP routes
Windows doesn’t add an IPv6 route by default. There are two workarounds:
Add a permanent default route manually using the following or a similar command
netsh interface ipv6 add route ::/0 interface=27
27is your IKEv2 interface ID or
netsh interface ipv6 add route ::/0 interface="<interface name>"
to avoid problems with interface ID change between reboots.
On Windows 10 and presumably all future versions where PowerShell is available, you can use MS PowerShell
Add-VpnConnectionRoutecmdlet. This cmdlet will not allow you add default route
0::/0. However in most cases you do not really need a default route over VPN. Current (as of 2/2020) IANA IPv6 space assignment specifies only the
2000::/3block as Global Unicast, and adding this prefix is perfectly sufficient for routing all traffic over the VPN interface. Cmdlet will will take care of adding the route upon VPN connection and also removing it upon disconnection. Also, unlike
netsh, this usually does not require administrator privileges and is fully integrated with the Windows GUI, saving you trouble with batch files.
Add-VpnConnectionRoute -ConnectionName "<interface name>" -DestinationPrefix "2000::/3"
The native Windows VPN Client does not send a responder identity (IDr) when initiating an IKE_SA, so two connection configurations can only be distinguished if their authentication type differs or the clients send different certificate for the different certificates' root CAs.
Windows doesn’t seem to be able to reach the VPN server’s physical IP address (to which the IKE_SA was established) via VPN connection. To access the server via VPN, use any other IP address that is assigned to it and included in the traffic selector (if necessary, assign an IP address to any local interface and maybe adjust the traffic selector).