3 Tinc is a VPN daemon which tunnels IP packets and Ethernet frames over UDP. More on Tinc can be found on: http://tinc-vpn.org Here I will show a tinc setup with an alpha (as a listening peer) and a beta (a peer connecting to alpha). After setting up the VPN, alpha will be the gateway for beta. All traffic from beta will be routed through alpha and back. I will basically retell the man page documentation: https://tinc-vpn.org/documentation-1.1/tinc.conf.5 but in a more tutorial kind of way.
6 Create config files /etc/tinc/gatewayvpn/tinc.conf
13 The name will be used by other tinc daemons for identification. Device in here means the virtual network to bind to. Because we are going to use routing we use a tunneling device. For alpha we don't fill out a ConnectTo option, so alpha will passively listen for incoming connections.
15 /etc/tinc/gatewayvpn/tinc-up
18 ip link set $INTERFACE up
19 ip addr add 172.16.16.1/24 dev $INTERFACE
22 This is a shell script executed right after the tinc daemon has been started and has connected to the virtual network device. It should be used to set up the corresponding network interface, but can also be used to start other things (as we show later for routing). $INTERFACE contains the name of our virtual network interface that the tinc daemon uses (in our case gatewayvpn). So later on, if you run tinc, it will show something like:
26 gatewayvpn Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00
27 inet addr:172.16.16.1 P-t-P:172.16.16.1 Mask:255.255.255.0
28 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
31 We use an IP address in the private range: 172.16.16.0/24, but you can use any address that you like (i.e. 10.0.0.0). The /24 means the subnet in which the daemon is going to serve. Here, we assing 172.16.16.1 to alpha.
33 /etc/tinc/gatewayvpn/tinc-down
37 ip addr del 172.16.16.1/24 dev $INTERFACE
38 ip link set $INTERFACE down
41 Shell script that will be executed right before the tinc daemon is going to close its connection to the virtual network device. Similar to tinc-up, but in reverse.
43 /etc/tinc/gatewayvpn/hosts/alpha
51 This file should be send to all the other peers (only beta in this example). We create this file here so we can automatically add a public key to this file. Since we want beta to connect to alpha we should assign the external IP and port number to it. Make sure this connection is accesible! We set the subnet to 0.0.0.0/0, you can read this as alpha serve on the whole internet (as opposed to a limiting it in a local range. If no Port option is specified, the socket will be bound to the standard port 655 of tinc.
53 === Create private keys ===
55 {{{ $ root@alpha tincd -n gatewayvpn --generate-keys
56 Generating 2048 bits keys: ...........
58 Please enter a file to save private RSA key to [/etc/tinc/gatewayvpn/rsa-key.priv]:
59 Please enter a file to save public RSA key to [/etc/tinc/gatewayvpn/hosts/alpha]:
62 Generate public/private RSA keypair. Private
63 key will be written to
64 /etc/tinc/gatewayvpn/rsa-key.priv. Public key
65 will be written to all the files in
66 /etc/tinc/gatewayvpn/hosts/. So after running
68 /etc/tinc/gatewayvpn/hosts/alpha will look
75 -----BEGIN RSA PUBLIC KEY-----
77 -----END RSA PUBLIC KEY-----
80 === Test your configuration ===
81 Now alpha is setup. We can test our configuration as follows:
84 root@alpha:~$ tincd -n gatewayvpn --logfile /root/log
88 The logfile should show the following output:
91 root@alpha:~# cat /root/log
92 2018-04-28 04:43:21 tinc.gatewayvpn[9589]: tincd 1.0.26 (Jul 5 2015 23:17:54) starting, debug level 0
93 2018-04-28 04:43:21 tinc.gatewayvpn[9589]: /dev/net/tun is a Linux tun/tap device (tun mode)
94 2018-04-28 04:43:21 tinc.gatewayvpn[9589]: Ready
97 You should also be able to ping to the tunneling device:
100 root@alpha:~$ ping 172.16.16.1
101 PING 172.16.16.1 (172.16.16.1) 56(84) bytes of data.
102 64 bytes from 172.16.16.1: icmp_seq=1 ttl=64 time=0.065 ms
103 64 bytes from 172.16.16.1: icmp_seq=2 ttl=64 time=0.060 ms
105 --- 172.16.16.1 ping statistics ---
106 2 packets transmitted, 2 received, 0% packet loss, time 999ms
107 rtt min/avg/max/mdev = 0.060/0.062/0.065/0.008 ms
110 The tinc daemon is listening on our configured port 7999:
113 root@alpha:~$ netstat -pnaut
114 tcp 0 0 0.0.0.0:7999 0.0.0.0: LISTEN 9828 tincd
115 udp 0 0 0.0.0.0:7999 0.0.0.0: 9828 tincd
120 Create config files /etc/tinc/gatewayvpn/tinc.conf
128 Beta will connect to alpha, for this connection beta will look in /etc/tinc/gatewayvpn/hosts/alpha and connect to this IP:PORT
130 /etc/tinc/gatewayvpn/tinc-up
134 ip link set $INTERFACE up
135 ip addr add 172.16.16.2/24 dev $INTERFACE
138 Beta will get assigned 172.16.16.2
140 /etc/tinc/gatewayvpn/tinc-down
144 ip addr del 172.16.16.2/24 dev $INTERFACE
145 ip link set $INTERFACE down
148 /etc/tinc/gatewayvpn/hosts/beta
151 Subnet = 172.16.16.2/32
155 We don't need to set a Address. No peer will actively connect to this peer. The subnet will be limited to just the the peer itself, since it is not serving in any local network.
157 === Create private keys ===
160 tincd -n gatewayvpn --generate-keys
161 Generating 2048 bits keys: ...........
163 Please enter a file to save private RSA key to [/etc/tinc/gatewayvpn/rsa_key.priv]:
164 Please enter a file to save public RSA key to [/etc/tinc/gatewayvpn/hosts/beta]:
167 So now you will also have created the private key file for beta. Public keys are written to files in the host directory. Note: don't forget to put /etc/tinc/gatewayvpn/hosts/beta on the alpha side and alpha on the beta side.
170 root@beta:/etc/tinc/gatewayvpn/hosts$ sudo scp root@alpha:/etc/tinc/gatewayvpn/hosts/alpha .
171 alpha 100% 481 0.5KB/s 00:00
172 root@beta:/etc/tinc/gatewayvpn/hosts$ sudo scp beta root@alpha:/etc/tinc/gatewayvpn/hosts/
173 beta 100% 463 0.5KB/s 00:00
176 === Test your configuration ===
180 Now let's see if the configuration is correct and both peers' connections are accepted. We, in a sense, have used a very verbose way to make a tunnel between two computers over the internet.
186 root@alpha:~$ tincd -n gatewayvpn --log-file /root/log
193 root@beta:~$ tincd -n gatewayvpn --log-file /root/log
196 Now test if you can ping!
199 root@alpha:~# ping 172.16.16.2
200 PING 172.16.16.2 (172.16.16.2) 56(84) bytes of data.
201 64 bytes from 172.16.16.2: icmp_seq=1 ttl=64 time=118 ms
202 64 bytes from 172.16.16.2: icmp_seq=2 ttl=64 time=118 ms
203 64 bytes from 172.16.16.2: icmp_seq=3 ttl=64 time=118 ms
204 root@beta:~# ping 172.16.16.1
206 PING 172.16.16.1 (172.16.16.1) 56(84) bytes of data.
207 64 bytes from 172.16.16.1: icmp_seq=1 ttl=64 time=118 ms
208 64 bytes from 172.16.16.1: icmp_seq=2 ttl=64 time=118 ms
209 64 bytes from 172.16.16.1: icmp_seq=3 ttl=64 time=117 ms
212 == Routing gateway ==
213 (Note: mostly copied from the tinc manual) It is possible to have one peer forward all of its network traffic to another peer on the VPN, effectively using this peer as the default gateway. This behaviour can configured in the tinc-up or tinc-down scripts. First, we explain some theory about redirecting, then the example scripts will follow.
216 Normally, there are two entries in the routing table. One is the route for the local network, which tells the kernel which IP addresses are directly reachable. The second is the "default gateway", which tells the kernel that in order to reach the rest of the Internet, traffic should be sent to the gateway of the local network. Usually the gateway is a router or firewall device, and its IPv4 address usually ends in .1. An example output of route -n on Linux:
218 Destination Gateway Genmask Flags Metric Ref Use Iface
219 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
220 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
223 Here, the LAN has the IPv4 address range 192.168.1.0/24, and the gateway is 192.168.1.1. Suppose we have a VPN with address range 172.16.16.0/24 (as in our case) on which a server (alpha in our setup) exists with address 172.16.16.1. If we have a VPN connection, and a peer wants to replace the standard default route with a default route pointing to 172.16.16.1, then there is a problem: the kernel does not know anymore how to send the encapsulated VPN packets to the server anymore. So we need to add an exception for traffic to the real (remote) IP address of the VPN server. Suppose its real address is 1.2.3.4, then the routing table should become:
225 Kernel IP routing table
226 Destination Gateway Genmask Flags Metric Ref Use Iface
227 172.16.16.1 0.0.0.0 255.255.255.255 UH 0 0 0 gatewayvpn
228 1.2.3.4 192.168.1.1 255.255.255.255 UGH 0 0 0 eth0
229 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
230 0.0.0.0 172.16.16.1 0.0.0.0 UG 0 0 0 gatewayvpn
233 This will ensure the local LAN is reachable, that the VPN server's real IP address is reachable via the original gateway, that the VPN server's VPN IP address is reachable on the vpn interface, and that all other traffic goes via the server on the VPN.
235 It is better not to remove the original default gateway route, since someone might kill the tincd process, such that it doesn't get a chance to restore the original. Instead, we use a trick where we add two /1 routes instead of one /0 route:
238 Kernel IP routing table
239 Destination Gateway Genmask Flags Metric Ref Use Iface
240 172.16.16.1 0.0.0.0 255.255.255.255 UH 0 0 0 gatewayvpn
241 1.2.3.4 192.168.1.1 255.255.255.255 UGH 0 0 0 eth0
242 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
243 128.0.0.0 172.16.16.1 128.0.0.0 UG 0 0 0 gatewayvpn
244 0.0.0.0 172.16.16.1 128.0.0.0 UG 0 0 0 gatewayvpn
245 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
248 Since both /1 cover all possible addresses, the real default route will never be used while the two /1 routes are present.
250 To achieve this, two scripts are needed on beta. We can add the following code to the the already existing tinc-up and tinc-down files.
252 /etc/tinc/gatewayvpn/tinc-up
256 VPN_GATEWAY=172.16.16.1
257 REMOTEADDRESS=1.2.3.4
258 ORIGINAL_GATEWAY=`ip route show | grep ^default | cut -d ' ' -f 2-5`
259 ip route add $REMOTEADDRESS $ORIGINAL_GATEWAY
260 ip route add $VPN_GATEWAY dev $INTERFACE
261 ip route add 0.0.0.0/1 via $VPN_GATEWAY dev $INTERFACE
262 ip route add 128.0.0.0/1 via $VPN_GATEWAY dev $INTERFACE
265 /etc/tinc/gatewayvpn/tinc-down
269 ORIGINAL_GATEWAY=`ip route show | grep ^default | cut -d ' ' -f 2-5`
270 REMOTEADDRESS=1.2.3.4
271 ip route del $REMOTEADDRESS $ORIGINAL_GATEWAY
272 ip route del $VPN_GATEWAY dev $INTERFACE
273 ip route del 0.0.0.0/1 dev $INTERFACE
274 ip route del 128.0.0.0/1 dev $INTERFACE
277 These script use the iproute2 commands, because they are easier to work with. The VPNGATEWAY and REMOTEADDRESS variables have to be filled in by hand. The ORIGINALGATEWAY variable copies the relevant information from the original default route to create the exception route to the VPN server.
280 Make sure forwarding is enabled on alpha. Make sure you have masquerading or another form of routing set up on alpha. If you don't masquerade outgoing (forwarded beta) packets, the source address in in the TCP/UDP package will still remain 172.16.16.2. Please have a look here: http://www.tldp.org/LDP/nag2/x-087-2-ipmasq.html if you don't know about NAT and masquerading.
283 # iptables config line to masquerade
285 echo "Enabling IPv4 forwarding"
286 echo 1 >/proc/sys/net/ipv4/ip_forward
288 echo "Appending Masquerade rule to iptables"
289 iptables -t nat -A POSTROUTING -s 172.16.16.0/255.255.255.0 -o eth0 -j MASQUERADE
292 Here I use iptables to masquerade the (-s) source address on the (-o) interface eth0.
294 == Test the gateway ==
295 Restart the daemon on alpha and beta. Use route -n to see check your routing table on beta. It should look similar to the one that is displayed above. Ping both the 172.16.16.1 and 1.2.3.4 (external address). In case of problems, trace the connections or analyze the data with tools like wireshark.
297 == Troubleshooting help ==
298 DNS request are not forwarded through the
299 gateway. Check your resolver config files
300 (/etc/resolv.conf). Debian-based systems
301 might have the following configuration:
304 root@beta:~$ cat /etc/resolv.conf
309 and in your routing table you might have the
310 following entry. A local / caching DNS server
311 might still send packages to your router. Use
312 wireshark to see if there are any DNS
313 queries, not going to the VPN gateway:
317 link-local * 255.255.0.0 U 1000 0 0 wlp7s0
320 A simple fix would to change your resolv.conf and point it to nameserver 8.8.8.8 Check your logfile while running tinc (i.e. you might forgot to create a key pair):
324 2018-04-28 04:49:53 tinc.gatewayvpn[9684]: Error reading RSA private key file
325 `/etc/tinc/gatewayvpn/rsa_key.priv': No such file or directory
328 Overview of created files
331 root@alpha:~$ ls -R /etc/tinc/gatewayvpn
332 /etc/tinc/gatewayvpn:
333 hosts/ rsa-key.priv tinc.conf tinc-down tinc-up
334 /etc/tinc/gatewayvpn/hosts:
339 root@beta:~$ ls -R /etc/tinc/gatewayvpn
340 /etc/tinc/gatewayvpn:
341 hosts/ rsa-key.priv tinc.conf tinc-down tinc-up
342 /etc/tinc/gatewayvpn/hosts:
346 Use tcpdump or wireshark to analyze your network devices