SSTP Server

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.

Certificates

Self Signed CA

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

vyos@vyos:~$ mkdir -p /config/user-data/sstp
vyos@vyos:~$ 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 []:

vyos@vyos:~$ 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 gateway-address <gateway>

Specifies single <gateway> IP address to be used as local address of PPP interfaces.

set vpn sstp port <port>

Specifies the port <port> that the SSTP port will listen on (default 443).

set vpn sstp client-ip-pool <POOL-NAME> range <x.x.x.x-x.x.x.x | x.x.x.x/x>

Use this command to define the first IP address of a pool of addresses to be given to SSTP clients. If notation x.x.x.x-x.x.x.x, it must be within a /24 subnet. If notation x.x.x.x/x is used there is possibility to set host/netmask.

set vpn sstp client-ip-pool <POOL-NAME> next-pool <NEXT-POOL-NAME>

Use this command to define the next address pool name.

set vpn sstp default-pool <POOL-NAME>

Use this command to define default address pool name.

set vpn sstp client-ipv6-pool <IPv6-POOL-NAME> prefix <address> mask <number-of-bits>

Use this comand to set the IPv6 address pool from which an SSTP client will get an IPv6 prefix of your defined length (mask) to terminate the SSTP endpoint at their side. The mask length can be set from 48 to 128 bit long, the default value is 64.

set vpn sstp client-ipv6-pool <IPv6-POOL-NAME> delegate <address> delegation-prefix <number-of-bits>

Use this command to configure DHCPv6 Prefix Delegation (RFC3633) on SSTP. You will have to set your IPv6 pool and the length of the delegation prefix. From the defined IPv6 pool you will be handing out networks of the defined length (delegation-prefix). The length of the delegation prefix can be set from 32 to 64 bit long.

set vpn sstp default-ipv6-pool <IPv6-POOL-NAME>

Use this command to define default IPv6 address pool name.

set vpn sstp name-server <address>

Connected client should use <address> as their DNS server. This command accepts both IPv4 and IPv6 addresses. Up to two nameservers can be configured for IPv4, up to three for IPv6.

Maximum number of IPv4 nameservers

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).

PPP Settings

set vpn sstp ppp-options disable-ccp

Disable Compression Control Protocol (CCP). CCP is enabled by default.

set vpn sstp ppp-options interface-cache <number>

Specifies number of interfaces to keep in cache. It means that don’t destroy interface after corresponding session is destroyed, instead place it to cache and use it later for new sessions repeatedly. This should reduce kernel-level interface creation/deletion rate lack. Default value is 0.

set vpn sstp ppp-options ipv4 <require | prefer | allow | deny>

Specifies IPv4 negotiation preference.

  • require - Require IPv4 negotiation

  • prefer - Ask client for IPv4 negotiation, do not fail if it rejects

  • allow - Negotiate IPv4 only if client requests (Default value)

  • deny - Do not negotiate IPv4

set vpn sstp ppp-options ipv6 <require | prefer | allow | deny>

Specifies IPv6 negotiation preference.

  • require - Require IPv6 negotiation

  • prefer - Ask client for IPv6 negotiation, do not fail if it rejects

  • allow - Negotiate IPv6 only if client requests

  • deny - Do not negotiate IPv6 (default value)

set vpn sstp ppp-options ipv6-accept-peer-interface-id

Accept peer interface identifier. By default is not defined.

set vpn sstp ppp-options ipv6-interface-id <random | x:x:x:x>

Specifies fixed or random interface identifier for IPv6. By default is fixed.

  • random - Random interface identifier for IPv6

  • x:x:x:x - Specify interface identifier for IPv6

set vpn sstp ppp-options ipv6-interface-id <random | x:x:x:x>

Specifies peer interface identifier for IPv6. By default is fixed.

  • random - Random interface identifier for IPv6

  • x:x:x:x - Specify interface identifier for IPv6

  • ipv4-addr - Calculate interface identifier from IPv4 address.

  • calling-sid - Calculate interface identifier from calling-station-id.

set vpn sstp ppp-options lcp-echo-failure <number>

Defines the maximum <number> of unanswered echo requests. Upon reaching the value <number>, the session will be reset. Default value is 3.

set vpn sstp ppp-options 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. Default value is 30.

set vpn sstp ppp-options 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. Default value is 0.

set vpn sstp ppp-options min-mtu <number>

Defines minimum acceptable MTU. If client will try to negotiate less then specified MTU then it will be NAKed or disconnected if rejects greater MTU. Default value is 100.

set vpn sstp ppp-options mppe <require | prefer | deny>

Specifies MPPE negotiation preference.

  • require - ask client for mppe, if it rejects drop connection

  • prefer - ask client for mppe, if it rejects don’t fail. (Default value)

  • 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.

set vpn sstp ppp-options mru <number>

Defines preferred MRU. By default is not defined.

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 vyos password vyos
set vpn sstp authentication mode local
set vpn sstp gateway-address 192.0.2.254
set vpn sstp client-ip-pool subnet 192.0.2.0/25
set vpn sstp name-server 10.0.0.1
set vpn sstp 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