Yggdrasil

End-to-end encrypted IPv6 networking to connect worlds

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Configuration

Yggdrasil can be run with a dynamically generated configuration, using sane-ish default settings, with yggdrasil --autoconf. In this mode, Yggdrasil will automatically attempt to peer with other nodes on the same subnet, but it also generates a random set of keys each time it is started, and therefore a random IP address.

In most cases, a static configuration simplifies most setups - it allows you to maintain the same IP address, configure static peers and various other options that will persist across restarts.

Yggdrasil supports configuration in either HJSON or JSON format. HJSON is the default preferred format, as it has comments, although JSON support is available due to ease of manipulation.

Generating Configuration

If you installed Yggdrasil through one of the platform packages (i.e. macOS, Debian, RPM) then a default configuration file may already exist in /etc/yggdrasil.conf.

Otherwise, you can generate a configuration file in the following ways:

Using Configuration

Yggdrasil can accept a configuration file either through stdin or by being given a path on the filesystem to a configuration file:

Normalising Configuration

If you want to see the original format of the configuration file, or convert between HJSON and JSON formats, you can use the -normaliseconf option, e.g.

Normalising the configuration also adds any missing configuration items with their default values. This can be useful when upgrading to a newer version of Yggdrasil that adds new configuration options. Many of our distribution packages normalise the configuration automatically during upgrade.

Configuration Layout

A new configuration file has the following format. Please note that some of the default values will vary from platform to platform.

{
  # Listen address for peer connections. Default is to listen for all
  # TCP connections over IPv4 and IPv6 with a random port.
  Listen: "[::]:xxxxx"

  # Listen address for admin connections Default is to listen for local
  # connections either on TCP/9001 or a UNIX socket depending on your
  # platform. Use this value for yggdrasilctl -endpoint=X.
  AdminListen: tcp://localhost:9001

  # List of connection strings for static peers in URI format, e.g.
  # tcp://a.b.c.d:e or socks://a.b.c.d:e/f.g.h.i:j.
  Peers: []

  # List of connection strings for static peers in URI format, arranged
  # by source interface, e.g. { "eth0": [ tcp://a.b.c.d:e ] }. Note that
  # SOCKS peerings will NOT be affected by this option and should go in
  # the "Peers" section instead.
  InterfacePeers: {}

  # Read timeout for connections, specified in milliseconds. If less
  # than 6000 and not negative, 6000 (the default) is used. If negative,
  # reads won't time out.
  ReadTimeout: 0

  # List of peer encryption public keys to allow or incoming TCP
  # connections from. If left empty/undefined then all connections
  # will be allowed by default.
  AllowedEncryptionPublicKeys: []

  # Your public encryption key. Your peers may ask you for this to put
  # into their AllowedEncryptionPublicKeys configuration.
  EncryptionPublicKey: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

  # Your private encryption key. DO NOT share this with anyone!
  EncryptionPrivateKey: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

  # Your public signing key. You should not ordinarily need to share
  # this with anyone.
  SigningPublicKey: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

  # Your private signing key. DO NOT share this with anyone!
  SigningPrivateKey: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

  # Regular expressions for which interfaces multicast peer discovery
  # should be enabled on. If none specified, multicast peer discovery is
  # disabled. The default value is .* which uses all interfaces.
  MulticastInterfaces:
  [
    .*
  ]

  # Local network interface name for TUN/TAP adapter, or "auto" to select
  # an interface automatically, or "none" to run without TUN/TAP.
  IfName: auto

  # Set local network interface to TAP mode rather than TUN mode if
  # supported by your platform - option will be ignored if not.
  IfTAPMode: false

  # Maximux Transmission Unit (MTU) size for your local TUN/TAP interface.
  # Default is the largest supported size for your platform. The lowest
  # possible value is 1280.
  IfMTU: 65535

  # The session firewall controls who can send/receive network traffic
  # to/from. This is useful if you want to protect this node without
  # resorting to using a real firewall. This does not affect traffic
  # being routed via this node to somewhere else. Rules are prioritised as
  # follows: blacklist, whitelist, always allow outgoing, direct, remote.
  SessionFirewall:
  {
    # Enable or disable the session firewall. If disabled, network traffic  
    # from any node will be allowed. If enabled, the below rules apply.
    Enable: false

    # Allow network traffic from directly connected peers.
    AllowFromDirect: true

    # Allow network traffic from remote nodes on the network that you are  
    # not directly peered with.
    AllowFromRemote: true

    # Allow outbound network traffic regardless of AllowFromDirect or  
    # AllowFromRemote. This does allow a remote node to send unsolicited  
    # traffic back to you for the length of the session.
    AlwaysAllowOutbound: false

    # List of public keys from which network traffic is always accepted,  
    # regardless of AllowFromDirect or AllowFromRemote.
    WhitelistEncryptionPublicKeys: []

    # List of public keys from which network traffic is always rejected,  
    # regardless of the whitelist, AllowFromDirect or AllowFromRemote.
    BlacklistEncryptionPublicKeys: []
  }

  # Allow tunneling non-Yggdrasil traffic over Yggdrasil. This effectively
  # allows you to use Yggdrasil to route to, or to bridge other networks,
  # similar to a VPN tunnel. Tunnelling works between any two nodes and
  # does not require them to be directly peered.
  TunnelRouting:
  {
    # Enable or disable tunnel routing.
    Enable: false

    # IPv6 CIDR subnets, mapped to the EncryptionPublicKey to which they  
    # should be routed, e.g. { "aaaa:bbbb:cccc::/e": "boxpubkey", ... }
    IPv6Destinations: {}

    # Optional IPv6 source subnets which are allowed to be tunnelled in  
    # addition to this node's Yggdrasil address/subnet. If not  
    # specified, only traffic originating from this node's Yggdrasil  
    # address or subnet will be tunnelled.
    IPv6Sources: []

    # IPv4 CIDR subnets, mapped to the EncryptionPublicKey to which they  
    # should be routed, e.g. { "a.b.c.d/e": "boxpubkey", ... }
    IPv4Destinations: {}

    # IPv4 source subnets which are allowed to be tunnelled. Unlike for  
    # IPv6, this option is required for bridging IPv4 traffic. Only  
    # traffic with a source matching these subnets will be tunnelled.
    IPv4Sources: []
  }

  # Advanced options for tuning the switch. Normally you will not need
  # to edit these options.
  SwitchOptions:
  {
    # Maximum size of all switch queues combined (in bytes).
    MaxTotalQueueSize: 4194304
  }

  # Optional node info. This must be a { "key": "value", ... } map
  # or set as null. This is entirely optional but, if set, is visible
  # to the whole network on request.
  NodeInfo: {}
}

Note that any field not specified in the configuration will use its default value, which may be random from run to run in the case of ports or keys.

Configuration Options

Use Cases

Manually Connecting to Peers

By default, only link-local auto-peering is enabled. This connects devices that are connected directly to each other at layer 2, including devices on the same LAN, directly connected by ethernet or configured to use the same ad-hoc wireless network.

As the network uses ordinary TCP, it is possible to connect over other networks, such as the Internet or WAN links, provided that the connecting node knows the address and port to connect to and that the connection is not blocked by a NAT or firewall. If the node resides behind a NAT, then port forwarding may be required in order to accept incoming connections.

By default, connections to peers are made over TCP. It is possible to route through a socks://proxyAddr:proxyPort/ connection. This uses TCP over the specified SOCKS proxy, and can be used to tunnel out from a network with a particularly restrictive firewall, for example, using SSH tunneling. This can also be used to connect over Tor, particularly for .onion hidden service addresses, although this does have a number of performance issues and is not generally recommended.

If you are unable to find nodes in the nearby area, a best effort is made to maintain a list of Public Peers for new users looking to join or test the network.

Advertising a Prefix

While it is generally encouraged that nodes run the software locally, to provide end-to-end cryptographic sessions and participate in routing, this is not always practical. Some network devices will inevitably be unable to run user code, but may still provide IPv6 connectivity. Users may also prefer to avoid running the software on an otherwise compatible system, perhaps to provide guest access or to avoid any overhead to battery powered devices. To that end, it is each node is assigned a /64 prefix in parallel to their address. A node acting as a router may advertise this prefix just as they would any other ordinary IPv6 network.

This may be best illustrated by example. Suppose a node has generated the address: 200:1111:2222:3333:4444:5555:6666:7777. Then the node may also use addresses from the prefix: 300:1111:2222:3333::/64 (note the 200 changed to 300, a separate /8 is used for prefixes, but the rest of the first 64 bits are the same).

On Linux, something like the following should be sufficient to advertise a prefix and a route to 200::/7 using radvd to a network attached to the eth0 interface:

  1. Enable IPv6 forwarding (e.g. sysctl -w net.ipv6.conf.all.forwarding=1 or add it to sysctl.conf).

  2. ip addr add 300:1111:2222:3333::1/64 dev eth0 or similar, to assign an address for the router to use in that prefix, where the LAN is reachable through eth0.

  3. Install/run radvd with something like the following in /etc/radvd.conf:

    interface eth0
    {
         AdvSendAdvert on;
         prefix 300:1111:2222:3333::/64 {
             AdvOnLink on;
             AdvAutonomous on;
         };
         route 200::/7 {};
    };
    

Note that a /64 prefix has fewer bits of address space available to check against the node’s ID, which in turn means hash collisions are more likely. As such, it is unwise to rely on addresses as a form of identify verification for the 300::/8 address range.

Generating Stronger Addresses (and Prefixes)

While 128 bits is long enough to make collisions technically impractical, if not outright impossible, it’s not unreasonable to think that 64 bits may be attackable at some point if not now. Without going too far into the details, addresses are a truncated hash of a node’s public key, with leading 1 bits accumulated and suppressed (along with the inevitable first 0 bit). Thanks to the accumulator, it is possible to brute force generate keys which include more bits of the node’s ID in the node’s IPv6 address, thereby making collisions more difficult. This can partially mitigate the fact that IPv6 addresses are only 128 bits long, and, more importantly, that prefixes are a mere 64 bits, 16 bits of which are sacrificed to the 200::/7 prefix and 1-byte accumulator in either case.

In short, if you plan to advertise a prefix, or if you want your address to be exceptionally difficult to collide with, then it is strongly advised that you burn some CPU cycles generating a harder-to-collide set of keys, using the following tool:

GOPATH=$PWD go run -tags debug misc/genkeys.go

This continually generates new keys and prints them out each time a new best set of keys is discovered. These keys may then be manually added to the configuration file.