SSTP

SSTP is a form of VPN tunnel that provides a mechanism to transport PPP traffic through an SSL/TLS channel. SSL/TLS provides transport-level security with key negotiation, encryption and traffic integrity checking. The use of SSL/TLS over TCP port 443 allows SSTP to pass through virtually all firewalls and proxy servers except for authenticated web proxies.

SSTP is available for Linux, BSD, and Windows.

VyOS utilizes accel-ppp to provide SSTP server functionality. We support both local and RADIUS authentication.

As SSTP provides PPP via a SSL/TLS channel the use of either publically signed certificates as well as a private PKI is required.

Note

All certificates should be stored on VyOS under /config/auth. If certificates are not stored in the /config directory they will not be migrated during a software update.

Self Signed CA and Certificates

To generate the CA, the server private key and certificates the following commands can be used.

[email protected]:~$ mkdir -p /config/user-data/sstp
[email protected]:~$ openssl req -newkey rsa:4096 -new -nodes -x509 -days 3650 -keyout /config/user-data/sstp/server.key -out /config/user-data/sstp/server.crt

Generating a 4096 bit RSA private key
.........................++
...............................................................++
writing new private key to 'server.key'
[...]
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:
Email Address []:

[email protected]:~$ openssl req -new -x509 -key /config/user-data/sstp/server.key -out /config/user-data/sstp/ca.crt
[...]
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:
Email Address []:

Configuration

set vpn sstp authentication local-users username <user> password <pass>
Create <user> for local authentication on this system. The users password will be set to <pass>.
set vpn sstp authentication local-users username <user> disable
Disable <user> account.
set vpn sstp authentication local-users username <user> static-ip <address>
Assign static IP address to <user> account.
set vpn sstp authentication local-users username <user> rate-limit download <bandwidth>
Download bandwidth limit in kbit/s for <user>.
set vpn sstp authentication local-users username <user> rate-limit upload <bandwidth>
Upload bandwidth limit in kbit/s for <user>.
set vpn sstp authentication protocols <pap | chap | mschap | mschap-v2>
Require the peer to authenticate itself using one of the following protocols: pap, chap, mschap, mschap-v2.
set vpn sstp authentication mode <local | radius>

Set authentication backend. The configured authentication backend is used for all queries.

  • radius: All authentication queries are handled by a configured RADIUS server.
  • local: All authentication queries are handled locally.
set vpn sstp network-settings client-ip-settings gateway-address <gateway>
Specifies single <gateway> IP address to be used as local address of PPP interfaces.
set vpn sstp network-settings client-ip-settings subnet <subnet>
Use <subnet> as the IP pool for all connecting clients.
set vpn sstp network-settings name-server <address>
Connected client should use <address> as their DNS server. Up to two IPv4 nameservers can be configured.

SSL Certificates

set vpn sstp ssl ca-cert-file <file>
Path to <file> pointing to the certificate authority certificate.
set vpn sstp ssl cert-file <file>
Path to <file> pointing to the servers certificate (public portion).
set vpn sstp ssl key-file <file>
Path to <file> pointing to the servers certificate (private portion).

PPP Settings

set vpn sstp ppp-settings lcp-echo-failure <number>
Defines the maximum <number> of unanswered echo requests. Upon reaching the value <number>, the session will be reset.
set vpn sstp ppp-settings lcp-echo-interval <interval>
If this option is specified and is greater than 0, then the PPP module will send LCP pings of the echo request every <interval> seconds.
set vpn sstp ppp-settings lcp-echo-timeout
Specifies timeout in seconds to wait for any peer activity. If this option specified it turns on adaptive lcp echo functionality and “lcp-echo-failure” is not used.
set vpn sstp ppp-settings mppe <require | prefer | deny>

Specifies MPPE negotioation preference.

  • require - ask client for mppe, if it rejects drop connection
  • prefer - ask client for mppe, if it rejects don’t fail
  • deny - deny mppe

Default behavior - don’t ask client for mppe, but allow it if client wants. Please note that RADIUS may override this option by MS-MPPE-Encryption-Policy attribute.

RADIUS

Server

set vpn sstp authentication radius server <server> port <port>
Configure RADIUS <server> and its required port for authentication requests.
set vpn sstp authentication radius server <server> key <secret>
Configure RADIUS <server> and its required shared <secret> for communicating with the RADIUS server.
set vpn sstp authentication radius server <server> fail-time <time>
Mark RADIUS server as offline for this given <time> in seconds.
set vpn sstp authentication radius server <server> disable
Temporary disable this RADIUS server.

Options

set vpn sstp authentication radius acct-timeout <timeout>
Timeout to wait reply for Interim-Update packets. (default 3 seconds)
set vpn sstp authentication radius dynamic-author server <address>
Specifies IP address for Dynamic Authorization Extension server (DM/CoA)
set vpn sstp authentication radius dynamic-author port <port>
Port for Dynamic Authorization Extension server (DM/CoA)
set vpn sstp authentication radius dynamic-author key <secret>
Secret for Dynamic Authorization Extension server (DM/CoA)
set vpn sstp authentication radius max-try <number>
Maximum number of tries to send Access-Request/Accounting-Request queries
set vpn sstp authentication radius timeout <timeout>
Timeout to wait response from server (seconds)
set vpn sstp authentication radius nas-identifier <identifier>
Value to send to RADIUS server in NAS-Identifier attribute and to be matched in DM/CoA requests.
set vpn sstp authentication radius nas-ip-address <address>
Value to send to RADIUS server in NAS-IP-Address attribute and to be matched in DM/CoA requests. Also DM/CoA server will bind to that address.
set vpn sstp authentication radius source-address <address>
Source IPv4 address used in all RADIUS server queires.
set vpn sstp authentication radius rate-limit attribute <attribute>
Specifies which RADIUS server attribute contains the rate limit information. The default attribute is Filter-Id.
set vpn sstp authentication radius rate-limit enable
Enables bandwidth shaping via RADIUS.
set vpn sstp authentication radius rate-limit vendor
Specifies the vendor dictionary, dictionary needs to be in /usr/share/accel-ppp/radius.

Example

  • Use local user foo with password bar
  • Client IP addresses will be provided from pool 192.0.2.0/25
set vpn sstp authentication local-users username foo password 'bar'
set vpn sstp authentication mode 'local'
set vpn sstp network-settings client-ip-settings gateway-address '192.0.2.254'
set vpn sstp network-settings client-ip-settings subnet '192.0.2.0/25'
set vpn sstp network-settings name-server '10.0.0.1'
set vpn sstp network-settings name-server '10.0.0.2'
set vpn sstp ssl ca-cert-file '/config/auth/ca.crt'
set vpn sstp ssl cert-file '/config/auth/server.crt'
set vpn sstp ssl key-file '/config/auth/server.key'

Testing SSTP

Once you have setup your SSTP server there comes the time to do some basic testing. The Linux client used for testing is called sstpc. sstpc requires a PPP configuration/peer file.

The following PPP configuration tests MSCHAP-v2:

$ cat /etc/ppp/peers/vyos
usepeerdns
#require-mppe
#require-pap
require-mschap-v2
noauth
lock
refuse-pap
refuse-eap
refuse-chap
refuse-mschap
#refuse-mschap-v2
nobsdcomp
nodeflate
debug

You can now “dial” the peer with the follwoing command: sstpc --log-level 4 --log-stderr --user vyos --password vyos vpn.example.com -- call vyos.

A connection attempt will be shown as:

$ sstpc --log-level 4 --log-stderr --user vyos --password vyos vpn.example.com -- call vyos

Mar 22 13:29:12 sstpc[12344]: Resolved vpn.example.com to 192.0.2.1
Mar 22 13:29:12 sstpc[12344]: Connected to vpn.example.com
Mar 22 13:29:12 sstpc[12344]: Sending Connect-Request Message
Mar 22 13:29:12 sstpc[12344]: SEND SSTP CRTL PKT(14)
Mar 22 13:29:12 sstpc[12344]:   TYPE(1): CONNECT REQUEST, ATTR(1):
Mar 22 13:29:12 sstpc[12344]:     ENCAP PROTO(1): 6
Mar 22 13:29:12 sstpc[12344]: RECV SSTP CRTL PKT(48)
Mar 22 13:29:12 sstpc[12344]:   TYPE(2): CONNECT ACK, ATTR(1):
Mar 22 13:29:12 sstpc[12344]:     CRYPTO BIND REQ(4): 40
Mar 22 13:29:12 sstpc[12344]: Started PPP Link Negotiation
Mar 22 13:29:15 sstpc[12344]: Sending Connected Message
Mar 22 13:29:15 sstpc[12344]: SEND SSTP CRTL PKT(112)
Mar 22 13:29:15 sstpc[12344]:   TYPE(4): CONNECTED, ATTR(1):
Mar 22 13:29:15 sstpc[12344]:     CRYPTO BIND(3): 104
Mar 22 13:29:15 sstpc[12344]: Connection Established

$ ip addr show ppp0
164: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1452 qdisc fq_codel state UNKNOWN group default qlen 3
     link/ppp  promiscuity 0
     inet 100.64.2.2 peer 100.64.1.1/32 scope global ppp0
        valid_lft forever preferred_lft forever