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vnet

A virtual network layer for pion.

Overview

Goals

To make NAT traversal tests easy.
To emulate packet impairment at application level for testing.
To monitor packets at specified arbitrary interfaces.

Features

Configurable virtual LAN and WAN
Virtually hosted ICE servers

Virtual network components

Top View

                           ......................................
                           :         Virtual Network (vnet)     :
                           :                                    :
   +-------+ *         1 +----+         +--------+              :
   | :App  |------------>|:Net|--o<-----|:Router |              :
   +-------+             +----+         |        |              :
   +-----------+ *     1 +----+         |        |              :
   |:STUNServer|-------->|:Net|--o<-----|        |              :
   +-----------+         +----+         |        |              :
   +-----------+ *     1 +----+         |        |              :
   |:TURNServer|-------->|:Net|--o<-----|        |              :
   +-----------+         +----+ [1]     |        |              :
                           :          1 |        | 1  <<has>>   :
                           :      +---<>|        |<>----+ [2]   :
                           :      |     +--------+      |       :
                         To form  |      *|             v 0..1  :
                   a subnet tree  |       o [3]      +-----+    :
                           :      |       ^          |:NAT |    :
                           :      |       |          +-----+    :
                           :      +-------+                     :
                           ......................................
    Note:
        o: NIC (Network Interface Controller)
      [1]: Net implements NIC interface.
      [2]: Root router has no NAT. All child routers have a NAT always.
      [3]: Router implements NIC interface for accesses from the
           parent router.

Net

Net provides 3 interfaces:

Configuration API (direct)
Network API via Net (equivalent to net.Xxx())
Router access via NIC interface

                   (Pion module/app, ICE servers, etc.)
                             +-----------+
                             |   :App    |
                             +-----------+
                                 * | 
                                   | <<uses>>
                                 1 v
   +---------+ 1           * +-----------+ 1    * +-----------+ 1    * +------+
 ..| :Router |----+------>o--|   :Net    |<>------|:Interface |<>------|:Addr |
   +---------+    |      NIC +-----------+        +-----------+        +------+
                  | <<interface>>             (transport.Interface)   (net.Addr)
                  |
                  |        * +-----------+ 1    * +-----------+ 1    * +------+
                  +------>o--|  :Router  |<>------|:Interface |<>------|:Addr |
                         NIC +-----------+        +-----------+        +------+
                    <<interface>>            (transport.Interface)    (net.Addr)

The instance of Net will be the one passed around the project. Net class has public methods for configuration and for application use.

Implementation

Design Policy

Each pion package should have config object which has Net (of type transport.Net) property.
- Just like how we distribute LoggerFactory throughout the pion project.
DNS => a simple dictionary (global)?
Each Net has routing capability (a goroutine)
Use interface provided net package as much as possible
Routers are connected in a tree structure (no loop is allowed)
- To simplify routing
- Easy to control / monitor (stats, etc)
Root router has no NAT (== Internet / WAN)
Non-root router has a NAT always
When a Net is instantiated, it will automatically add lo0 and eth0 interface, and lo0 will have one IP address, 127.0.0.1. (this is not used in pion/ice, however)
When a Net is added to a router, the router automatically assign an IP address for eth0 interface.
- For simplicity
User data won't fragment, but optionally drop chunk larger than MTU
IPv6 is not supported

Basic steps for setting up virtual network

Create a root router (WAN)
Create child routers and add to its parent (forms a tree, don't create a loop!)
Add instances of Net to each routers
Call Stop(), or Stop(), on the top router, which propagates all other routers

Example: WAN with one endpoint (vnet)

import (
	"net"

    "github.com/pion/transport"
	"github.com/pion/transport/vnet"
	"github.com/pion/logging"
)

// Create WAN (a root router).
wan, err := vnet.NewRouter(&RouterConfig{
    CIDR:          "0.0.0.0/0",
    LoggerFactory: logging.NewDefaultLoggerFactory(),
})

// Create a network.
// You can specify a static IP for the instance of Net to use. If not specified,
// router will assign an IP address that is contained in the router's CIDR.
nw := vnet.NewNet(&vnet.NetConfig{
    StaticIP: "27.1.2.3",
})

// Add the network to the router.
// The router will assign an IP address to `nw`.
if err = wan.AddNet(nw); err != nil {
    // handle error
}

// Start router.
// This will start internal goroutine to route packets.
// If you set child routers (using AddRouter), the call on the root router
// will start the rest of routers for you.
if err = wan.Start(); err != nil {
    // handle error
}

//
// Your application runs here using `nw`.
//

// Stop the router.
// This will stop all internal Go routines in the router tree.
// (No need to call Stop() on child routers)
if err = wan.Stop(); err != nil {
    // handle error
}

Example of how to pass around the instance of vnet.Net

The instance of vnet.Net wraps a subset of net package to enable operations on the virtual network. Your project must be able to pass the instance to all your routines that do network operation with net package. A typical way is to use a config param to create your instances with the virtual network instance (nw in the above example) like this:

type AgentConfig struct {
    :
    Net:  transport.Net,
}

type Agent struct {
     :
    net:  transport.Net,
}

func NetAgent(config *AgentConfig) *Agent {
    if config.Net == nil {
        config.Net = vnet.NewNet()
    }
    
    return &Agent {
         :
        net: config.Net,
    }
}

// a.net is the instance of vnet.Net class
func (a *Agent) listenUDP(...) error {
    conn, err := a.net.ListenPacket(udpString, ...)
    if err != nil {
        return nil, err
    }
      :
}

Compatibility and Support Status

`net` (built-in)	`vnet`	Note
net.Interfaces()	a.net.Interfaces()
net.InterfaceByName()	a.net.InterfaceByName()
net.ResolveUDPAddr()	a.net.ResolveUDPAddr()
net.ListenPacket()	a.net.ListenPacket()
net.ListenUDP()	a.net.ListenUDP()	ListenPacket() is recommended
net.Listen()	a.net.Listen()	TODO)
net.ListenTCP()	(not supported)	Listen() would be recommended
net.Dial()	a.net.Dial()
net.DialUDP()	a.net.DialUDP()
net.DialTCP()	(not supported)
net.Interface	transport.Interface
net.PacketConn	(use it as-is)
net.UDPConn	transport.UDPConn
net.TCPConn	transport.TCPConn	TODO: Use net.Conn in your code
net.Dialer	transport.Dialer	Use a.net.CreateDialer() to create it. The use of vnet.Dialer is currently experimental.

a.net is an instance of Net class, and types are defined under the package name vnet

Most of other interface types in net package can be used as is.

Please post a github issue when other types/methods need to be added to vnet/vnet.Net.

TODO / Next Step

Implement TCP (TCPConn, Listen)
Support of IPv6
Write a bunch of examples for building virtual networks.
Add network impairment features (on Router)
- Introduce latency / jitter
- Packet filtering handler (allow selectively drop packets, etc.)
Add statistics data retrieval
- Total number of packets forward by each router
- Total number of packet loss
- Total number of connection failure (TCP)

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