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Port Forwarding

Port forwarding is divided into TCP and UDP port forwarding according to the protocol type, and local forwarding and remote forwarding according to the forwarding type. There are four combinations in total.

Local Port Forwarding

TCP

You can set a single forwarding destination address for one-to-one port forwarding:

gost -L tcp://:8080/192.168.1.1:80
services:
- name: service-0
  addr: :8080
  handler:
    type: tcp
  listener:
    type: tcp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80

Map the local TCP port 8080 to port 80 of 192.168.1.1, and all data to the local port 8080 will be forwarded to 192.168.1.1:80.

You can also set multiple destination addresses for one-to-many port forwarding:

gost -L tcp://:8080/192.168.1.1:80,192.168.1.2:80,192.168.1.3:8080?strategy=round&maxFails=1&failTimeout=30s
services:
- name: service-0
  addr: :8080
  handler:
    type: tcp
  listener:
    type: tcp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80
    - name: target-1
      addr: 192.168.1.2:80
    - name: target-2
      addr: 192.168.1.3:8080
    selector:
      strategy: round
      maxFails: 1
      failTimeout: 30s

After each forwarding request is received, the node selector in the forwarder will be used to select a node in the target address list as the target address of this forwarding.

UDP

Similar to TCP port forwarding, single and multiple destination forwarding addresses can also be specified.

gost -L udp://:10053/192.168.1.1:53,192.168.1.2:53,192.168.1.3:53?keepAlive=true&ttl=5s
services:
- name: service-0
  addr: :10053
  handler:
    type: udp
  listener:
    type: udp
    metadata:
      keepAlive: true
      ttl: 5s
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:53
    - name: target-1
      addr: 192.168.1.2:53
    - name: target-2
      addr: 192.168.1.3:53

Each client corresponds to a forwarding channel. When the keepAlive option is set to false, the channel will be closed immediately after the requested response data is returned to the client.

When the keepAlive option is set to true, the forwarding service does not receive data from the forwarding target host within a certain period of time, and the forwarding channel will be marked as idle. The forwarding service internally checks whether the forwarding channel is idle according to the period specified by the ttl option (default value is 5 seconds). If it is idle, the channel will be closed. An idle channel will be closed for at most two check cycles.

Forwarding Chain

Port forwarding can be used in conjunction with forwarding chains to perform indirect forwarding.

gost -L=tcp://:8080/192.168.1.1:80 -F socks5://192.168.1.2:1080
services:
- name: service-0
  addr: :8080
  handler:
    type: tcp
    chain: chain-0
  listener:
    type: tcp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:1080
      connector:
        type: socks5
      dialer:
        type: tcp

Map the local TCP port 8080 to port 80 of 192.168.1.1 through the forwarding chain.

gost -L=udp://:10053/192.168.1.1:53 -F socks5://192.168.1.2:1080
services:
- name: service-0
  addr: :10053
  handler:
    type: udp
    chain: chain-0
  listener:
    type: udp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:53
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:1080
      connector:
        type: socks5
      dialer:
        type: tcp

Map the local UDP port 10053 to port 53 of 192.168.1.1 through the forwarding chain.

Limitation

When forwarding chains are used in UDP local port forwarding, the last node at the end of the forwarding chain must be of the following type:

  • GOST HTTP proxy service and enable UDP forwarding function, using UDP-over-TCP method.
    gost -L http://:8080?udp=true
    
  • GOST SOCKS5 proxy service and enable UDP forwarding function, using UDP-over-TCP method.
    gost -L socks5://:1080?udp=true
    
  • Relay service, using UDP-over-TCP method.
  • SSU service.

UDP-over-TCP

UDP-over-TCP refers to using a TCP connection to transmit UDP datagrams. In GOST, this statement may not be accurate. For example, SOCKS5 is used for UDP port forwarding. SOCKS5 services can be based on TCP type transport channels (TLS, Websocket, etc.) or UDP type transport channels (KCP, QUIC, etc.), it is more appropriate to use UDP-over-Stream here (as opposed to the unreliable datagram transmission of UDP), any reliable streaming protocol can be used here.

SSH

TCP port forwarding can be indirectly forwarded by means of the port forwarding function of the standard SSH protocol

gost -L=tcp://:8080/192.168.1.1:80 -F sshd://user:pass@192.168.1.2:22
services:
- name: service-0
  addr: :8080
  handler:
    type: tcp
    chain: chain-0
  listener:
    type: tcp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:22
      connector:
        type: sshd
      dialer:
        type: sshd
        auth:
          username: user
          password: pass

The 192.168.1.2:22 service here can be the standard SSH service of the system itself, or the sshd type service of GOST

gost -L sshd://user:pass@:22
services:
- name: service-0
  addr: :22
  handler:
    type: sshd
  listener:
    type: sshd
    auth:
      username: user
      password: pass

Remote Port Forwarding

TCP

gost -L rtcp://:8080/192.168.1.1:80
services:
- name: service-0
  addr: :8080
  handler:
    type: rtcp
  listener:
    type: rtcp
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80

Map the local TCP port 8080 to port 80 of 192.168.1.1, and all data to the local port 8080 will be forwarded to 192.168.1.1:80.

UDP

gost -L rudp://:10053/192.168.1.1:53,192.168.1.2:53,192.168.1.3:53?ttl=5s
services:
- name: service-0
  addr: :10053
  handler:
    type: rudp
  listener:
    type: rudp
    metadata:
      ttl: 5s
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:53
    - name: target-1
      addr: 192.168.1.2:53
    - name: target-2
      addr: 192.168.1.3:53

Note

Remote port forwarding is no different from local port forwarding without the use of forwarding chains.

Forwarding Chain

gost -L=rtcp://:8080/192.168.1.1:80 -F socks5://192.168.1.2:1080
services:
- name: service-0
  addr: :8080
  handler:
    type: rtcp
  listener:
    type: rtcp
    chain: chain-0
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:1080
      connector:
        type: socks5
      dialer:
        type: tcp

According to the address specified by the rtcp service, listen on the 8080 TCP port on the host 192.168.1.2 through the forwarding chain. After receiving the request, it forwards the data to the rtcp service through the forwarding chain, and the rtcp service forwards the request to port 192.168.1.1:80.

gost -L=rudp://:10053/192.168.1.1:53 -F socks5://192.168.1.2:1080
services:
- name: service-0
  addr: :10053
  handler:
    type: rudp
  listener:
    type: rudp
    chain: chain-0
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:53
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:1080
      connector:
        type: socks5
      dialer:
        type: tcp

According to the address specified by the rudp service, listen on port 10053 on the host 192.168.1.2 through the forwarding chain. After receiving the request, it forwards the data to the rudp service through the forwarding chain, and the rudp service forwards the request to port 192.168.1.1:53.

Note

The forwarding chain on remote port forwarding is set on the listener by default, and another forwarding chain can also be set on the handler at the same time.

The listening address in the remote port forwarding service will listen on the host where the service of the last node at the end of the forwarding chain is located when using the forwarding chain.

Limitation

When forwarding chains are used in remote port forwarding, the last node at the end of the forwarding chain must be of the following type:

  • GOST SOCKS5 proxy service and enable BIND function, using UDP-over-TCP method.
    gost -L socks5://:1080?bind=true
    
  • Relay service and enable BIND function, using UDP-over-TCP method.
    gost -L socks5://:8421?bind=true
    

SSH

TCP remote port forwarding can be indirectly forwarded by means of the remote port forwarding function of the standard SSH protocol:

gost -L=rtcp://:8080/192.168.1.1:80 -F sshd://user:pass@192.168.1.2:22
services:
- name: service-0
  addr: :8080
  handler:
    type: rtcp
  listener:
    type: rtcp
    chain: chain-0
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.2:22
      connector:
        type: sshd
      dialer:
        type: sshd
        auth:
          username: user
          password: pass

The 192.168.1.2:22 service here can be the standard SSH service of the system itself, or the sshd type service of GOST.

Server-side Forwarding

The above forwarding method can be regarded as client forwarding, and the client controls the forwarding target address. The target address can also be specified by the server.

Server

gost -L tls://:8443/192.168.1.1:80
services:
- name: service-0
  addr: :8080
  handler:
    type: forward
  listener:
    type: tls
  forwarder:
    nodes:
    - name: target-0
      addr: 192.168.1.1:80

Client

gost -L=tcp://:8080 -F forward+tls://:8443
services:
- name: service-0
  addr: :8080
  handler:
    type: tcp
  listener:
    type: tcp
    chain: chain-0
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: :8443
      connector:
        type: forward
      dialer:
        type: tls

forward type connector and handler

The handler of this service and the connector of the forwarding chain must be of type forward. Since the target address is specified by the server, the client does not need to specify the target address. The forward connector does not do any logic processing.

Here tcp://:8080 is equivalent to tcp://:8080/:0, and the forwarding destination address :0 is here as a placeholder. This usage is only valid when used with the forward connector.