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Client

Introduction

For a long time, the modern usage and principles of proxy clients for graphical operating systems have not been clearly described. However, we can categorize them into three types: system proxy, firewall redirection, and virtual interface.

System Proxy

Almost all graphical environments support system-level proxies, which are essentially ordinary HTTP proxies that only support TCP.

Operating System / Desktop Environment System Proxy Application Support
Windows
macOS
GNOME/KDE
Android ROOT or adb (permission) is required
Android/iOS (with sing-box graphical client) via tun.platform.http_proxy

As one of the most well-known proxy methods, it has many shortcomings: many TCP clients that are not based on HTTP do not check and use the system proxy. Moreover, UDP and ICMP traffics bypass the proxy.

flowchart LR
    dns[DNS query] -- Is HTTP request? --> proxy[HTTP proxy]
    dns --> leak[Leak]
    tcp[TCP connection] -- Is HTTP request? --> proxy
    tcp -- Check and use HTTP CONNECT? --> proxy
    tcp --> leak
    udp[UDP packet] --> leak

Firewall Redirection

This type of usage typically relies on the firewall or hook interface provided by the operating system, such as Windows’ WFP, Linux’s redirect, TProxy and eBPF, and macOS’s pf. Although it is intrusive and cumbersome to configure, it remains popular within the community of amateur proxy open source projects like V2Ray, due to the low technical requirements it imposes on the software.

Virtual Interface

All L2/L3 proxies (seriously defined VPNs, such as OpenVPN, WireGuard) are based on virtual network interfaces, which is also the only way for all L4 proxies to work as VPNs on mobile platforms like Android, iOS.

The sing-box inherits and develops clash-premium’s TUN inbound (L3 to L4 conversion) as the most reasonable method for performing transparent proxying.

flowchart TB
    packet[IP Packet]
    packet --> windows[Windows / macOS]
    packet --> linux[Linux]
    tun[TUN interface]
    windows -. route .-> tun
    linux -. iproute2 route/rule .-> tun
    tun --> gvisor[gVisor TUN stack]
    tun --> system[system TUN stack]
    assemble([L3 to L4 assemble])
    gvisor --> assemble
    system --> assemble
    assemble --> conn[TCP and UDP connections]
    conn --> router[sing-box Router]
    router --> direct[Direct outbound]
    router --> proxy[Proxy outbounds]
    router -- DNS hijack --> dns_out[DNS outbound]
    dns_out --> dns_router[DNS router]
    dns_router --> router
    direct --> adi([auto detect interface])
    proxy --> adi
    adi --> default[Default network interface in the system]
    default --> destination[Destination server]
    default --> proxy_server[Proxy server]
    proxy_server --> destination

Examples

Basic TUN usage for Chinese users

{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "223.5.5.5",
        "detour": "direct"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      }
    ],
    "strategy": "ipv4_only"
  },
  "inbounds": [
    {
      "type": "tun",
      "inet4_address": "172.19.0.1/30",
      "auto_route": true,
      "strict_route": false
    }
  ],
  "outbounds": [
    // ...
    {
      "type": "direct",
      "tag": "direct"
    },
    {
      "type": "dns",
      "tag": "dns-out"
    }
  ],
  "route": {
    "rules": [
      {
        "protocol": "dns",
        "outbound": "dns-out"
      },
      {
        "geoip": [
          "private"
        ],
        "outbound": "direct"
      }
    ],
    "auto_detect_interface": true
  }
}
{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "223.5.5.5",
        "detour": "direct"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      }
    ]
  },
  "inbounds": [
    {
      "type": "tun",
      "inet4_address": "172.19.0.1/30",
      "inet6_address": "fdfe:dcba:9876::1/126",
      "auto_route": true,
      "strict_route": false
    }
  ],
  "outbounds": [
    // ...
    {
      "type": "direct",
      "tag": "direct"
    },
    {
      "type": "dns",
      "tag": "dns-out"
    }
  ],
  "route": {
    "rules": [
      {
        "protocol": "dns",
        "outbound": "dns-out"
      },
      {
        "geoip": [
          "private"
        ],
        "outbound": "direct"
      }
    ],
    "auto_detect_interface": true
  }
}
{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "223.5.5.5",
        "detour": "direct"
      },
      {
        "tag": "remote",
        "address": "fakeip"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      },
      {
        "query_type": [
          "A",
          "AAAA"
        ],
        "server": "remote"
      }
    ],
    "fakeip": {
      "enabled": true,
      "inet4_range": "198.18.0.0/15",
      "inet6_range": "fc00::/18"
    },
    "independent_cache": true
  },
  "inbounds": [
    {
      "type": "tun",
      "inet4_address": "172.19.0.1/30",
      "inet6_address": "fdfe:dcba:9876::1/126",
      "auto_route": true,
      "strict_route": true
    }
  ],
  "outbounds": [
    // ...
    {
      "type": "direct",
      "tag": "direct"
    },
    {
      "type": "dns",
      "tag": "dns-out"
    }
  ],
  "route": {
    "rules": [
      {
        "protocol": "dns",
        "outbound": "dns-out"
      },
      {
        "geoip": [
          "private"
        ],
        "outbound": "direct"
      }
    ],
    "auto_detect_interface": true
  }
}

Traffic bypass usage for Chinese users

{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "223.5.5.5",
        "detour": "direct"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      },
      {
        "clash_mode": "Direct",
        "server": "local"
      },
      {
        "clash_mode": "Global",
        "server": "google"
      },
      {
        "rule_set": "geosite-geolocation-cn",
        "server": "local"
      }
    ]
  },
  "route": {
    "rule_set": [
      {
        "type": "remote",
        "tag": "geosite-geolocation-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geosite/rule-set/geosite-geolocation-cn.srs"
      }
    ]
  }
}
{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "https://223.5.5.5/dns-query",
        "detour": "direct"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      },
      {
        "clash_mode": "Direct",
        "server": "local"
      },
      {
        "clash_mode": "Global",
        "server": "google"
      },
      {
        "rule_set": "geosite-geolocation-cn",
        "server": "local"
      },
      {
        "clash_mode": "Default",
        "server": "google"
      },
      {
        "rule_set": "geoip-cn",
        "server": "local"
      }
    ]
  },
  "route": {
    "rule_set": [
      {
        "type": "remote",
        "tag": "geosite-geolocation-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geosite/rule-set/geosite-geolocation-cn.srs"
      },
      {
        "type": "remote",
        "tag": "geoip-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geoip/rule-set/geoip-cn.srs"
      }
    ]
  },
  "experimental": {
    "clash_api": {
      "default_mode": "Leak"
    }
  }
}
{
  "dns": {
    "servers": [
      {
        "tag": "google",
        "address": "tls://8.8.8.8"
      },
      {
        "tag": "local",
        "address": "https://223.5.5.5/dns-query",
        "detour": "direct"
      }
    ],
    "rules": [
      {
        "outbound": "any",
        "server": "local"
      },
      {
        "clash_mode": "Direct",
        "server": "local"
      },
      {
        "clash_mode": "Global",
        "server": "google"
      },
      {
        "rule_set": "geosite-geolocation-cn",
        "server": "local"
      },
      {
        "rule_set": "geoip-cn",
        "server": "google",
        "client_subnet": "114.114.114.114" // Any China client IP address
      }
    ]
  },
  "route": {
    "rule_set": [
      {
        "type": "remote",
        "tag": "geosite-geolocation-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geosite/rule-set/geosite-geolocation-cn.srs"
      },
      {
        "type": "remote",
        "tag": "geoip-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geoip/rule-set/geoip-cn.srs"
      }
    ]
  }
}
{
  "outbounds": [
    {
      "type": "direct",
      "tag": "direct"
    },
    {
      "type": "block",
      "tag": "block"
    }
  ],
  "route": {
    "rules": [
      {
        "type": "logical",
        "mode": "or",
        "rules": [
          {
            "protocol": "dns"
          },
          {
            "port": 53
          }
        ],
        "outbound": "dns"
      },
      {
        "ip_is_private": true,
        "outbound": "direct"
      },
      {
        "clash_mode": "Direct",
        "outbound": "direct"
      },
      {
        "clash_mode": "Global",
        "outbound": "default"
      },
      {
        "type": "logical",
        "mode": "or",
        "rules": [
          {
            "port": 853
          },
          {
            "network": "udp",
            "port": 443
          },
          {
            "protocol": "stun"
          }
        ],
        "outbound": "block"
      },
      {
        "rule_set": [
          "geoip-cn",
          "geosite-geolocation-cn"
        ],
        "outbound": "direct"
      }
    ],
    "rule_set": [
      {
        "type": "remote",
        "tag": "geoip-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geoip/rule-set/geoip-cn.srs"
      },
      {
        "type": "remote",
        "tag": "geosite-geolocation-cn",
        "format": "binary",
        "url": "https://raw.githubusercontent.com/SagerNet/sing-geosite/rule-set/geosite-geolocation-cn.srs"
      }
    ]
  }
}