Transparent Proxy¶

Transparent proxy supports two modes: REDIRECT and TPROXY. The REDIRECT mode only supports TCP.

Limitation

Transparent proxy is only available on Linux.

Traffic Sniffing

The TCP transparent proxy supports the detection of HTTP and TLS traffic. The HTTP Host header information or the SNI extension information of TLS is used as the target access address.

Traffic sniffing is enabled through the sniffing option, which is not enabled by default.

REDIRECT¶

Transparent proxy using REDIRECT can choose to mark packets. Using Mark requires administrator privileges to run.

Without Mark¶

CLIFile (YAML)

gost -L red://:12345?sniffing=true -F 192.168.1.1:1080

services:
- name: service-0
  addr: :12345
  handler:
    type: red
    chain: chain-0
    metadata:
      sniffing: true
  listener:
    type: red
chains:
- name: chain-0
  hops:
  - name: hop-0
    nodes:
    - name: node-0
      addr: 192.168.1.1:1080
      connector:
        type: http
      dialer:
        type: tcp

iptables-Local Global TCP Proxy

iptables -t nat -A OUTPUT -p tcp --match multiport ! --dports 12345,1080 -j DNAT --to-destination 127.0.0.1:12345

With Mark¶

Using Mark can avoid an infinite loop caused by secondary interception of egress traffic.

CLIFile (YAML)

gost -L "red://:12345?sniffing=true&so_mark=100"

services:
- name: service-0
  addr: :12345
  sockopts:
    mark: 100
  handler:
    type: red
    metadata:
      sniffing: true
  listener:
    type: red

Forwarding Chain¶

CLIFile (YAML)

gost -L red://:12345?sniffing=true -F "http://192.168.1.1:1080?so_mark=100"

services:
- name: service-0
  addr: :12345
  handler:
    type: red
    chain: chain-0
    metadata:
      sniffing: true
  listener:
    type: red
chains:
- name: chain-0
  hops:
  - name: hop-0
    sockopts:
      mark: 100  
    nodes:
    - name: node-0
      addr: 192.168.1.1:1080
      # node level sockopts, will override hop level value.
      # sockopts:
      #   mark: 100  
      connector:
        type: http
      dialer:
        type: tcp

Set the mark value via the so_mark (command line) or sockopts (config file) parameter.

iptables Rules

iptables -t nat -N GOST
# Ignore LAN traffic, please adjust it according to the actual network environment
iptables -t nat -A GOST -d 192.168.0.0/16 -j RETURN
# Ignore egress traffic
iptables -t nat -A GOST -p tcp -m mark --mark 100 -j RETURN
# Redirect TCP traffic to port 12345
iptables -t nat -A GOST -p tcp -j REDIRECT --to-ports 12345
# Intercept LAN traffic
iptables -t nat -A PREROUTING -p tcp -j GOST
iptables -t nat -A OUTPUT -p tcp -j GOST

TPROXY¶

TCP¶

CLIFile (YAML)

gost -L "red://:12345?sniffing=true&tproxy=true&so_mark=100"

services:
- name: service-0
  addr: :12345
  sockopts:
    mark: 100  
  handler:
    type: red
    metadata:
      sniffing: true
      tproxy: true
  listener:
    type: red
    metadata:
      tproxy: true

Forwarding Chain¶

CLIFile (YAML)

gost -L "red://:12345?sniffing=true&tproxy=true" -F http://192.168.1.1:8080?so_mark=100

services:
- name: service-0
  addr: :12345
  handler:
    type: red
    chain: chain-0
    metadata:
      sniffing: true
      tproxy: true
  listener:
    type: red
    metadata:
      tproxy: true
chains:
- name: chain-0
  hops:
  - name: hop-0
    sockopts:
      mark: 100  
    nodes:
    - name: node-0
      addr: 192.168.1.1:8080
      connector:
        type: http
      dialer:
        type: tcp

Routing and iptables Rules

# ipv4
ip rule add fwmark 1 lookup 100
ip route add local default dev lo table 100

iptables -t mangle -N DIVERT
iptables -t mangle -A DIVERT -j MARK --set-mark 1
iptables -t mangle -A DIVERT -j ACCEPT
iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT

iptables -t mangle -N GOST
iptables -t mangle -A GOST -p tcp -d 127.0.0.0/8 -j RETURN
iptables -t mangle -A GOST -p tcp -d 192.168.0.0/16 -j RETURN
iptables -t mangle -A GOST -p tcp -m mark --mark 100 -j RETURN 
iptables -t mangle -A GOST -p tcp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
iptables -t mangle -A PREROUTING -p tcp -j GOST

# Only for local mode
iptables -t mangle -N GOST_LOCAL
iptables -t mangle -A GOST_LOCAL -p tcp -d 127.0.0.0/8 -j RETURN
iptables -t mangle -A GOST_LOCAL -p tcp -d 255.255.255.255/32 -j RETURN
iptables -t mangle -A GOST_LOCAL -p tcp -d 192.168.0.0/16 -j RETURN
iptables -t mangle -A GOST_LOCAL -p tcp -m mark --mark 100 -j RETURN 
iptables -t mangle -A GOST_LOCAL -p tcp -j MARK --set-mark 1
iptables -t mangle -A OUTPUT -p tcp -j GOST_LOCAL

# ipv6
ip -6 rule add fwmark 1 lookup 100
ip -6 route add local default dev lo table 100
ip6tables -t mangle -N DIVERT
ip6tables -t mangle -A DIVERT -j MARK --set-mark 1
ip6tables -t mangle -A DIVERT -j ACCEPT
ip6tables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT

ip6tables -t mangle -N GOST
ip6tables -t mangle -A GOST -p tcp -d ::/128 -j RETURN
ip6tables -t mangle -A GOST -p tcp -d ::1/128 -j RETURN
ip6tables -t mangle -A GOST -p tcp -d fe80::/10 -j RETURN
ip6tables -t mangle -A GOST -p tcp -d ff00::/8 -j RETURN
ip6tables -t mangle -A GOST -p tcp -m mark --mark 100 -j RETURN 
ip6tables -t mangle -A GOST -p tcp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
ip6tables -t mangle -A PREROUTING -p tcp -j GOST

# Only for local mode
ip6tables -t mangle -N GOST_LOCAL
ip6tables -t mangle -A GOST_LOCAL -p tcp -d ::/128 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p tcp -d ::1/128 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p tcp -d fe80::/10 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p tcp -d ff00::/8 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p tcp -m mark --mark 100 -j RETURN 
ip6tables -t mangle -A GOST_LOCAL -p tcp -j MARK --set-mark 1
ip6tables -t mangle -A OUTPUT -p tcp -j GOST_LOCAL

UDP¶

CLIFile (YAML)

gost -L "redu://:12345?ttl=30s&so_mark=100"

services:
- name: service-0
  addr: :12345
  sockopts:
    mark: 100  
  handler:
    type: redu
  listener:
    type: redu
    metadata:
      ttl: 30s

Forwarding Chain¶

CLIFile (YAML)

gost -L redu://:12345?ttl=30s -F relay://192.168.1.1:8421?so_mark=100

services:
- name: service-0
  addr: :12345
  handler:
    type: redu
    chain: chain-0
  listener:
    type: redu
    metadata:
      ttl: 30s
chains:
- name: chain-0
  hops:
  - name: hop-0
    sockopts:
      mark: 100  
    nodes:
    - name: node-0
      addr: 192.168.1.1:8421
      connector:
        type: relay
      dialer:
        type: tcp

ttl (duration, default=30s): UDP tunnel timeout period.
readBufferSize (int, default=4096): UDP read buffer size

Routing and iptables Rules

# ipv4
ip rule add fwmark 1 lookup 100
ip route add local default dev lo table 100

iptables -t mangle -N GOST
iptables -t mangle -A GOST -p udp -d 127.0.0.0/8 -j RETURN
iptables -t mangle -A GOST -p udp -d 255.255.255.255/32 -j RETURN
iptables -t mangle -A GOST -p udp -d 192.168.0.0/16 -j RETURN
iptables -t mangle -A GOST -p udp -m mark --mark 100 -j RETURN 
iptables -t mangle -A GOST -p udp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
iptables -t mangle -A PREROUTING -p udp -j GOST

# Only for local mode
iptables -t mangle -N GOST_LOCAL
iptables -t mangle -A GOST_LOCAL -p udp -d 127.0.0.0/8 -j RETURN
iptables -t mangle -A GOST_LOCAL -p udp -d 255.255.255.255/32 -j RETURN
iptables -t mangle -A GOST_LOCAL -p udp -d 192.168.0.0/16 -j RETURN
iptables -t mangle -A GOST_LOCAL -p udp -m mark --mark 100 -j RETURN 
iptables -t mangle -A GOST_LOCAL -p udp -j MARK --set-mark 1
iptables -t mangle -A OUTPUT -p udp -j GOST_LOCAL

# ipv6
ip -6 rule add fwmark 1 lookup 100
ip -6 route add local default dev lo table 100

ip6tables -t mangle -N GOST
ip6tables -t mangle -A GOST -p udp -d ::/128 -j RETURN
ip6tables -t mangle -A GOST -p udp -d ::1/128 -j RETURN
ip6tables -t mangle -A GOST -p udp -d fe80::/10 -j RETURN
ip6tables -t mangle -A GOST -p udp -d ff00::/8 -j RETURN
ip6tables -t mangle -A GOST -p udp -m mark --mark 100 -j RETURN 
ip6tables -t mangle -A GOST -p udp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
ip6tables -t mangle -A PREROUTING -p udp -j GOST

# Only for local mode
ip6tables -t mangle -N GOST_LOCAL
ip6tables -t mangle -A GOST_LOCAL -p udp -d ::/128 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p udp -d ::1/128 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p udp -d fe80::/10 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p udp -d ff00::/8 -j RETURN
ip6tables -t mangle -A GOST_LOCAL -p udp -m mark --mark 100 -j RETURN 
ip6tables -t mangle -A GOST_LOCAL -p udp -j MARK --set-mark 1
ip6tables -t mangle -A OUTPUT -p udp -j GOST_LOCAL

Playground¶

The network namespace allows you to build a test environment on a single machine without affecting the normal network settings. Here, ns1 is used to simulate the gateway, ns2 is used to simulate the client, and the default namespace is used to simulate the target host.

Create a new network namespace ns1, and interconnect it with the default namespace through veth0 (10.0.10.1/24) and veth1 (10.0.10.2/24) pair.

ip netns add ns1
ip link add dev veth0 type veth peer name veth1 netns ns1
ip addr add 10.0.10.1/24 dev veth0
ip link set dev veth0 up
ip -n ns1 addr add 10.0.10.2/24 dev veth1
ip -n ns1 link set dev lo up
ip -n ns1 link set dev veth1 up

Create a new network namespace ns2, and interconnect namespace ns2 with ns1 through veth2 (10.0.20.1/24) and veth3 (10.0.20.2/24) pair. Namespace ns2 uses ns1 as the gateway.

ip netns add ns2
ip netns exec ns1 ip link add veth2 type veth peer name veth3 netns ns2
ip netns exec ns1 ip addr add 10.0.20.1/24 dev veth2
ip netns exec ns1 ip link set veth2 up
ip netns exec ns2 ip addr add 10.0.20.2/24 dev veth3
ip netns exec ns2 ip link set veth3 up
ip netns exec ns2 ip link set lo up
ip netns exec ns2 ip route add default via 10.0.20.1 dev veth3

Configure routing and iptables rules in namespace ns1.

ip netns exec ns1 ip rule add fwmark 1 lookup 100
ip netns exec ns1 ip route add local default dev lo table 100

# TCP
ip netns exec ns1 iptables -t mangle -N DIVERT
ip netns exec ns1 iptables -t mangle -A DIVERT -j MARK --set-mark 1
ip netns exec ns1 iptables -t mangle -A DIVERT -j ACCEPT
ip netns exec ns1 iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT

ip netns exec ns1 iptables -t mangle -N GOST
ip netns exec ns1 iptables -t mangle -A GOST -p tcp -d 127.0.0.0/8 -j RETURN
ip netns exec ns1 iptables -t mangle -A GOST -p tcp -d 255.255.255.255/32 -j RETURN
ip netns exec ns1 iptables -t mangle -A GOST -p tcp -m mark --mark 100 -j RETURN 
ip netns exec ns1 iptables -t mangle -A GOST -p tcp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
ip netns exec ns1 iptables -t mangle -A PREROUTING -p tcp -j GOST

# UDP
ip netns exec ns1 iptables -t mangle -A GOST -p udp -d 127.0.0.0/8 -j RETURN
ip netns exec ns1 iptables -t mangle -A GOST -p udp -d 255.255.255.255/32 -j RETURN
ip netns exec ns1 iptables -t mangle -A GOST -p udp -m mark --mark 100 -j RETURN 
ip netns exec ns1 iptables -t mangle -A GOST -p udp -j TPROXY --tproxy-mark 0x1/0x1 --on-port 12345 
ip netns exec ns1 iptables -t mangle -A PREROUTING -p udp -j GOST

Start relay service in default namespace.

gost -L relay://:8420

Run GOST transparent proxy (TCP/UDP) in namespace ns1 and forward through the relay proxy service of the default namespace.

ip netns exec ns1 gost -L "red://:12345?tproxy=true" -L "redu://:12345?ttl=30s" -F "relay://10.0.10.1:8420?so_mark=100"

Run the iperf3 service in the default namespace.

iperf3 -s

Execute iperf test in namespace ns2.

# TCP
ip netns exec ns2 iperf3 -c 10.0.10.1

# UDP
ip netns exec ns2 iperf3 -c 10.0.10.1 -u

Cleaning

ip netns delete ns1
ip netns delete ns2

Transparent Proxy¶

REDIRECT¶

Without Mark¶

With Mark¶

Forwarding Chain¶

TPROXY¶

TCP¶

Forwarding Chain¶

UDP¶

Forwarding Chain¶

Playground¶

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