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vpncloud/vpncloud.adoc

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vpncloud(1)

Name

vpncloud - Peer-to-peer VPN

SYNOPSIS

vpncloud [options] [--config <file>] [-p <password>] [-l <addr>] [-c <addr>…]

OPTIONS

--config <file>

Read configuration options from the specified file. Please see the section CONFIG FILES for documentation on the file format. If the same option is defined in the config file and as a parameter, the parameter overrides the config file.

-t <type>, --type <type>

Set the type of network. There are two options: tap devices process Ethernet frames tun devices process IP packets. [default: tun]

-d <name>, --device <name>

Name of the virtual device. Any %d will be filled with a free number. [default: vpncloud%d]

--device-path <path>

The path of the base device inode, e.g. /dev/net/tun.

--fix-rp-filter

If this option is set, VpnCloud will change the rp_filter settings to protect against a potential system vulnerability. See SECURITY for more info.

-m <mode>, --mode <mode>

The mode of the VPN. The VPN can like a router, a switch or a hub. A hub will send all data always to all peers. A switch will learn addresses from incoming data and only send data to all peers when the address is unknown. A router will send data according to known subnets of the peers and ignore them otherwise. The normal mode is switch for tap devices and router for tun devices. [default: normal]

-l <addr>, --listen <addr>

The address on which to listen for data. This can be simply a port number or a full address in form IP:PORT. If the IP is specified as '*' or only a port number is given, then the socket will listen on all IPs (v4 and v6), otherwise the socket will only listen on the given IP. Alternatively, a websocket proxy URL (starting with ws://) can be given here. Please see the section *WEBSOCKET PROXY* for more info. [default: 3210]

-c <addr>, --peer <addr>, --connect <addr>

Address of a peer to connect to. The address should be in the form addr:port. If the node is not started, the connection will be retried periodically. This parameter can be repeated to connect to multiple peers.

--claim <subnet>

The local subnets to claim. This parameter should be in the form address/prefixlen where address is an IPv4 address, an IPv6 address, or a MAC address. The prefix length is the number of significant front bits that distinguish the subnet from other subnets. Example: 10.1.1.0/24.

--no-auto-claim

Do not automatically claim the IP set on the virtual interface (on TUN devices).

-p <password>, --password <password>

A password to encrypt the VPN data. This parameter must be set unless a password is given in a config file or a private key is set. See SECURITY for more info.

--key <key>, --private-key <key>

A private key to use for encryption. The key must be given as base62 as generated by genkey. See SECURITY for more info.

--public-key <key>

A public key matching the given private key. The key must be given as base62 as generated by genkey. This argument is purely optional. See SECURITY for more info.

--trust <key>, *--trusted-key <key>

A public key to trust. Any peer must have a key pair that is trusted by this node, otherwise it will be rejected. The key must be given as base62 as generated by genkey. This argument can be given multiple times. If it is not set, only the own public key will be trusted. See SECURITY for more info.

--algo <method>, --algorithm <method>

Supported encryption algorithms ("plain", "aes128", "aes256", or "chacha20"). Nodes exchange the supported algorithms and select the one that is fastest on both ends. This parameter can be given multiple times to enable multiple algorithms. Warning: "plain" means unencrypted and needs to be enabled explicitly. As default, all algorithms except "plain" are enabled.

--peer-timeout <secs>

Peer timeout in seconds. The peers will exchange information periodically and drop peers that are silent for this period of time. [default: 300]

--keepalive <secs>

Interval of peer exchange messages in seconds. The peers will exchange information periodically to keep connections alive. This setting overrides how often this will happen. [default: peer-timeout/2-60]

--switch-timeout <secs>

Switch table entry timeout in seconds. This parameter is only used in switch mode. Addresses that have not been seen for the given period of time will be forgotten. [default: 300]

--beacon-store <path|command>

Periodically store beacons containing the address of this node in the given file or via the given command. If the parameter value starts with a pipe character (|), the rest of the value is interpreted as a shell command. Otherwise the value is interpreted as a file to write the beacon to. If this parameter is not given, beacon storage is disabled. Please see the section BEACONS for more information.

--beacon-load <path|command>

Periodically load beacons containing the addresses of other nodes from the given file or via the given command. If the parameter value starts with a pipe character (|), the rest of the value is interpreted as a shell command. Otherwise the value is interpreted as a file to read the beacon from. If this parameter is not given, beacon loading is disabled. Please see the section BEACONS for more information.

--beacon-interval <secs>

Beacon storage/loading interval in seconds. If configured to do so via --beacon-store and --beacon-load, the node will periodically store its beacon and load beacons of other nodes. This parameter defines the interval in seconds. [default: 3600]

--beacon-password <password>

An optional password to use to encrypt all beacon data. See the section BEACONS for more information.

--ip <address>

An IP address (plus optional prefix length) for the interface. If this argument is given, the address (and if a prefix length is given, also the netmask) is configured on the device and the device is activated. If also --ifup is given, the interface is configured before the ifup command is executed. Please see DEVICE SETUP for more info.

--ifup <command>

A command to setup the network interface. The command will be run (as parameter to sh -c) when the device has been created to configure it. The name of the allocated device will be available via the environment variable IFNAME. Please note that this command is executed with the full permissions of the caller. Please see DEVICE SETUP for more info.

--ifdown <command>

A command to bring down the network interface. The command will be run (as parameter to sh -c) to remove any configuration from the device. The name of the allocated device will be available via the environment variable IFNAME. Please note that this command is executed with the (limited) permissions of the user and group given as --user and --group.

--pid-file <file>

Store the process id in this file when running in the background. If set, the given file will be created containing the process id of the new background process. This option is only used when running in background.

--user <user>
--group <group>

Change the user and/or group of the process once all the setup has been done.

--log-file <file>

If set, print logs also to the given file. The file will be created and truncated if is exists.

--stats-file <file>

If set, periodically write statistics on peers and current traffic to the given file. The file will be periodically overwritten with new data.

--statsd-server <server>

If set, periodically send statistics on current traffic and some important events to the given statsd server (host:port). Please see STATSD SUPPORT for more info.

--statsd-prefix <prefix>

Sets the prefix to use for all statsd entries. [default: vpncloud] Please see STATSD SUPPORT for more info.

--daemon

Spawn a background process instead of running the process in the foreground. If this flag is set, the process will first carry out all the initialization, then drop permissions if --user or --group is used and then spawn a background process and write its process id to a file if --pid-file is set. Then, the main process will exit and the background process continues to provide the VPN. At the time, when the main process exits, the interface exists and is properly configured to be used.

--no-port-forwarding

Disable automatic port forward. If this option is not set, VpnCloud tries to detect a NAT router and automatically add a port forwarding to it.

--hook <script>

Call the given script on an event. If the script is in the format event:script, it will only be called for the specified event type, otherwise it will be called for all events. This parameter can be given multiple times. Please see the section HOOK SCRIPTS for more info.

-v, --verbose

Print debug information, including information for data being received and sent.

-q, --quiet

Only print errors and warnings.

-h, --help

Display the help.

SUBCOMMANDS

The following subcommands can be given to run some special action instead of running a VpnCloud instance. Any parameters must be given after the subcommand name (except for -v -q and -h). Only the listed parameters are accepted for the subcommands.

genkey

Generate and print a random key pair and exit. The key pair is printed as base62 and can be used as private-key, public-key and trusted-key options. See SECURITY for more info.

-p <password>, --password <password>

Derive the key pair from the given password instead of creating randomly.

ws-proxy

Run a websocket proxy instead of the normal VpnCloud instance. See WEBSOCKET PROXY for more info.

-l <addr>, --listen <addr>

Listen on the given TCP address (IP:PORT or PORT). [default: 3210]

migrate-config

Migrate an old config to the current config format.

--config-file

The path of the config file to convert.

completion

Output shell completions for the VpnCloud command.

--shell

The shell type to create completions for. [default: bash]

DESCRIPTION

VpnCloud is a peer-to-peer VPN over UDP. It creates a virtual network interface on the host and forwards all received data via UDP to the destination. It can work in 3 different modes:

Switch mode

In this mode, the VPN will dynamically learn addresses as they are used as source addresses by peers and use them to forward data to its destination. Addresses that have not been seen for some time (option switch_timeout) will be forgotten. Data for unknown addresses will be broadcast to all peers. This mode is the default mode for TAP devices that process Ethernet frames but it can also be used with TUN devices and IP packets.

Hub mode

In this mode, all data will always be broadcast to all peers. This mode uses lots of bandwidth and should only be used in special cases.

Router mode

In this mode, data will be forwarded based on preconfigured address ranges ("claims"). Data for unclaimed addresses will be silently ignored. This mode is the default mode for TUN devices that work with IP packets but it can also be used with TAP devices and Ethernet frames.

All connected VpnCloud nodes will form a peer-to-peer network and cross-connect automatically until the network is fully connected. The nodes will periodically exchange information with the other nodes to signal that they are still active and to allow the automatic cross-connect behavior. There are some important things to note:

  1. The cross-connect behavior can be able to connect nodes that are behind firewalls or NATs as it can function as hole-punching.

  2. The management traffic will increase with the peer number quadratically. It should still be reasonably small for high node numbers (below 10 KiB/s for 10.000 nodes). A longer peer_timeout can be used to reduce the traffic further. For high node numbers, router mode should be used as it never broadcasts data.

VpnCloud does not implement any loop-avoidance. Since data received on the UDP socket will only be sent to the local network interface and vice versa, VpnCloud cannot produce loops on its own. On a TAP device, however STP data can be transported to avoid loops caused by other network components.

For TAP devices, IEEE 802.1q frames (VLAN tagged) are detected and forwarded based on separate MAC tables. Any nested tags (Q-in-Q) will be ignored.

EXAMPLES

Simple multi-node connectivity

In the example scenario, a simple layer-3 network tunnel is established. Most likely those commands need to be run as root using sudo.

First, VpnCloud need to be started on both nodes (the address after -c is the address of the remote node and the the X in the interface address must be unique among all nodes, e.g. 0, 1, 2, …):

vpncloud -c REMOTE_HOST:PORT --ip 10.0.0.X/24 --password PASSWORD

Afterwards, the interface can be used to communicate.

Routed TUN example

In this example, 2 nodes and their subnets should communicate using IP. First, VpnCloud need to be started on both nodes:

vpncloud -t tun -c REMOTE_HOST:PORT --ip 10.0.X.1 --claim 10.0.X.0/24 --password PASSWORD

It is important to configure the interface in a way that all addresses on the VPN can be reached directly. E.g. if subnets 10.0.1.0/24, 10.0.2.0/24 and so on are used, the interface needs to be configured as 10.0.1.1/16. For TUN devices, this means that the prefix length of the subnets (/24 in this example) must be different than the prefix length that the interface is configured with (/16 in this example).

Important notes

  1. VpnCloud can be used to connect two separate networks. TAP networks can be bridged using brctl and TUN networks must be routed. It is very important to be careful when setting up such a scenario in order to avoid network loops, security issues, DHCP issues and many more problems.

  2. TAP devices will forward DHCP data. If done intentionally, this can be used to assign unique addresses to all participants. If this happens accidentally, it can conflict with DHCP servers of the local network and can have severe side effects.

CONFIG FILES

The config file is a YAML file that contains configuration values. All entries are optional and override the defaults. Please see the section OPTIONS for detailed descriptions of the options.

device

A key-value map with device settings

type

Set the type of network. Same as --type

name

Name of the virtual device. Same as --device

path

Set the path of the base device. Same as --device-path

fix-rp-filter

Fix the rp_filter settings on the host. Same as --fix-rp-filter

ip

An IP address (plus optional prefix length) for the interface. Same as --ip

ifup

A command to setup the network interface. Same as --ifup

ifdown

A command to bring down the network interface. Same as --ifdown

crypto

A key-value map with crypto settings

algorithms

The encryption algorithms to support. See --algorithm

password

The password to use for encryption. Same as --password

private-key

The private key to use. Same as --private-key

public-key

The public key to use. Same as --public-key

trusted-keys

Other public keys to trust. See --trusted-key

listen

The address on which to listen for data. Same as --listen

peers

A list of addresses to connect to. See --connect

peer_timeout

Peer timeout in seconds. Same as --peer-timeout

keepalive

Periodically send message to keep connections alive. Same as --keepalive

beacon

A key-value map with beacon settings

store

Path or command to store beacons. Same as --beacon-store

load

Path or command to load beacons. Same as --beacon-load

interval

Interval for loading and storing beacons in seconds. Same as --beacon-interval

password

Password to encrypt the beacon with. Same as --beacon-password

mode

The mode of the VPN. Same as --mode

switch_timeout

Switch table entry timeout in seconds. Same as --switch-timeout

claims

A list of local subnets to claim. See --claim

auto-claim

Whether to automatically claim the device ip. See --no-auto-claim

port_forwarding

Whether to activate port forwardig. See --no-port-forwarding

user

The name of a user to run the background process under. Same as --user

group

The name of a group to run the background process under. Same as --group

pid_file

The path of the pid file to create. Same as --pid-file

stats_file

The path of the statistics file. Same as --stats-file

statsd

A key-value map with statsd settings

server

Server to report statistics to. Same as --statsd-server

prefix

Prefix to use when reporting to statsd. Same as --statsd-prefix

hook

A hook script to be called for every event type. See HOOK SCRIPTS for info.

hooks

A map of event type to script for scripts that only fire for one event type. See HOOK SCRIPTS for info.

Example

device:
  type: tun
  name: vpncloud%d
ip: 10.0.1.1/16
crypto:
  password: mysecret
listen: 3210
peers:
  - remote.machine.foo:3210
  - remote.machine.bar:3210
peer_timeout: 600
mode: normal
claims:
  - 10.0.1.0/24
port_forwarding: true
user: nobody
group: nogroup
pid_file: /run/vpncloud.pid

SECURITY

VpnCloud uses strong cryptography based on modern cryptographic primitives.

Before exchanging any payload data with peers a secure connection is initialized based on key pairs. Each node has a key pair consisting of a private and a public key (--private-key and --public-key). Those key pairs can be generated via genkey. To allow connections, nodes need to list the public keys of all other nodes as trusted keys (--trusted-key). To simplify the key exchange, key pairs can be derived from passwords (--password). If no trusted keys are configured, nodes will only trust their own public key. Nodes configured with the same password will therefore trust each others.

In the initialization phase of the connection, nodes agree on a temporary key that is used to encrypt the next messages using a fast encryption algorithm. VpnCloud automatically benchmarks all supported algorithms and negotiates to use the fastest algorithm for each connection. Users can limit the supported algorithms if they wish using --algorithm. Although highly discouraged, users can opt out of encryption altogether by enabling the plain algorithm. (Note: both nodes in a connection must support this, otherwise encryption will take place.)

The temporary encryption keys are rotated periodically so they are never used for a longer time.

Please refer to the security whitepaper for more details.

CVE-2019-14899

The Linux kernel contains a vulnerability that affects all VPNs disregarding of the specific technology being used. Under some circumstances, the kernel accepts packets for the address range configured on the vpn interface also on other interfaces. This way, an attacker can test the presence of a VPN and find out the IPs being used. Also the attacker can with some effort inject data and manipulate connections that should be protected by the VPN. To mitigate this, the rp_filter setting should be configured to strict mode, which unfortunately a lot of distributions do not set as default. VpnCloud will detect this misconfiguration and offers to fix it via --fix-rp-filter. Note: This vulnerability affects all VPN technologies as it is not located in the VPN software but in the Linux kernel.

BEACONS

Beacons are short character sequences that contain a timestamp and a list of addresses. They can be published and retrieved by other nodes to find peers without the need for static addresses.

The beacons are short (less than 100 characters), encrypted and encoded with printable characters to allow publishing them in various places on the internet, e.g.:

  • On shared drives or synchronized folders (e.g. on Dropbox)

  • Via a dedicated database

  • Via a general purpose message board of message service (e.g. Twitter)

The beacons are very robust. They only consist of alphanumeric characters and can be interleaved with non-alphanumeric characters (e.g. whitespace). Also the beacons contain a prefix and suffix that depends on the configured network magic and secret key (if set) so that all nodes can find beacons in a long text.

When beacons are stored or loaded via a command (using the pipe character |), the command is interpreted using the configured shell sh. This command has access to the following environment variables:

$begin

The prefix of the beacon.

$end

The suffix of the beacon.

$data (only on store)

The middle part of the beacon. Do not use this without prefix and suffix!

$beacon (only on store)

The full beacon consisting of prefix, data and suffix. The commands are called in separate threads, so even longer running commands will not block the node.

STATSD SUPPORT

When a statsd server is configured (either via --statsd-server or the config option statsd_server), VpnCloud sends out the following statistics every minute.

Gauge values: peer_count:: Current number of peers table_entries:: Number of routing table / switch table entries

The following statistics consist of two keys: .bytes and .packets that hold the values in bytes and packets. All values refer to the traffic during the last minute: traffic.protocol.inbound:: Complete incoming traffic with all peers traffic.protocol.outbound:: Complete outgoing traffic with all peers traffic.payload.inbound:: Incoming payload traffic with all peers traffic.payload.outbound:: Outgoing payload traffic with all peers invalid_protocol_traffic:: Invalid incoming protocol traffic dropped_payload:: Outgoing traffic that could not be routed

All keys are prefixed by a common prefix. The prefix defaults to vpncloud but can be changed via --statsd-prefix or the config option statsd_prefix.

WEBSOCKET PROXY

The websocket proxy mode replaces the local UDP port by a websocket proxy to allow connectivity even in very restricted environments.

This means that instead of listening on a local port for incoming messages and sending outgoing messages via this port, all UDP traffic will be forwarded to and received from a remote proxy via the websocket protocol. This proxy opens a UDP port for each VpnCloud instance that connects to it. The instance can use this port remotely just like it would use a real local UDP port.

The proxy is transparent, it does not manipulate or even decrypt the messages it forwards. Trust relations are still created between VpnCloud instances, not between an instance and the proxy. The proxy only ever sees encrypted messages. Therefore, the connection to it uses plain HTTP.

A websocket proxy can be stared by using the ws-proxy subcommand. A custom port can be set using the --listen parameter. (Note that this port never conflicts with a VpnCloud port on the same machine since VpnCloud uses UDP and the proxy uses TCP.)

A VpnCloud instance can use a websocket proxy instead of opening a local port by specifying the websocket proxy via its --listen parameter (e.g. --listen ws://example.com:3210). Note that the websocket URL must start with ws:\/\/, not http:\/\/.

HOOK SCRIPTS

VpnCloud supports calling hook scripts on certain events. The scripts can either be configured on the command line or in the config file. Hook scripts can either be configured per event type or globally.

When an event occurs, the specified hook script is executed using the current permissions of the user that started the instance. Note that this means that if VpnCloud is configured to drop permissions, only the events device_setup and device_configured will be executed using root permissions.

Hook scripts are executed using sh -c, so either binaries, shell scripts and even shell commands can be used. The script will be executed in parallel to the VpnCloud instance. Its output will be printed to the stdout of VpnCloud and the return code is ignored.

The hook script will receive information on the event using environment variables. The variable EVENT will contain the name of the event. Other variables depend on the event type.

The following event types

peer_connecting

A new peer connection is in the process of being established. The variable PEER contains the address of the peer but no other information is known at that point in time. Variables: IFNAME, PEER

peer_connected

A new peer successfully connected to this instance. Besides the peer address, also a list of claims (CLAIMS, space separated) and the node id of the new peer (NODE_ID) are given to the script. Variables: IFNAME, PEER, CLAIMS, NODE_ID

peer_disconnected

A peer connection has been closed. If the peer has been fully connected, the node id is given (NODE_ID). Variables: IFNAME, PEER, (NODE_ID)

device_setup

This event is fired when the virtual device has been created but not yet configured. Variables: IFNAME

device_configured

This event is fired when the virtual device is fully configured. Variables: IFNAME

vpn_started

This event is fired when the VPN is ready to be used. Variables: IFNAME

vpn_shutdown

This event is fired when the VPN s shutting down. Variables: IFNAME

DEVICE SETUP

The device is setup using the following steps:

  1. The device is created with the type and name given as --type and --device.

  2. Depending on the device type and the main network device of the systme, the optimal MTU is determined and configured on the device.

  3. If and IP address (and optional prefix length) is given via --ip, the interface is configured with the address and the given netmask (default: 255.255.255.0). Also the interface is set to be active.

  4. If a command is given as --ifup, the given command will be executed. The name of the interface is stored in an environment variable as "IFNAME". Note that VpnCloud waits for the command to exit before starting its normal operation.

Note that most of the steps will need elevated permissions, so the vpncloud command needs to be executed as root (e.g. via sudo). Beware that the ifup command will also be executed using those permissions.

VpnCloud can drop the elevated permissions when --user and --group is given.

Copyright © 2015-2021 Dennis Schwerdel This software is licensed under GPL-3 or newer (see LICENSE.md)