Dynamic Port Forwarding (SOCKS Proxy)¶

Overview¶

Dynamic port forwarding creates a SOCKS proxy that routes all traffic through the SSH connection. Unlike local/remote forwarding (single destination), dynamic forwarding works for any destination.

┌──────────────────────────────────────────────────────────────────────────┐
│                     Dynamic Port Forwarding (SOCKS)                       │
│                                                                           │
│   Your Machine            SSH Server              Internet                │
│   ┌───────────┐          ┌───────────┐          ┌───────────┐           │
│   │           │          │           │          │           │           │
│   │   SOCKS   │──────────┤   SSH     │──────────┤  Any Site │           │
│   │   :1080   │  SSH     │  Server   │  Normal  │           │           │
│   │           │  Tunnel  │           │  Traffic │           │           │
│   └───────────┘          └───────────┘          └───────────┘           │
│                                                                           │
│   Browser -> SOCKS proxy -> SSH -> google.com, github.com, etc.            │
│                                                                           │
└──────────────────────────────────────────────────────────────────────────┘

Use cases: Browse internet as if from remote server, bypass geo-restrictions, secure browsing on untrusted networks.

Basic Syntax¶

ssh -D [bind_address:]port user@ssh_server

Basic Usage¶

Create SOCKS Proxy¶

ssh -D 1080 user@server.example.com

Creates a SOCKS5 proxy on localhost:1080.

Tunnel Only¶

ssh -D 1080 -N user@server.example.com

Background¶

ssh -D 1080 -f -N user@server.example.com

Browser Configuration¶

Firefox¶

Settings -> Network Settings -> Settings
Manual proxy configuration
SOCKS Host: 127.0.0.1, Port: 1080
SOCKS v5
Check "Proxy DNS when using SOCKS v5"

Chrome¶

Chrome uses system proxy, or launch with flags:

google-chrome --proxy-server="socks5://127.0.0.1:1080"

System-Wide (macOS)¶

System Preferences -> Network -> Advanced -> Proxies: - Check "SOCKS Proxy" - Server: 127.0.0.1:1080

System-Wide (Linux)¶

export ALL_PROXY=socks5://127.0.0.1:1080
export HTTP_PROXY=socks5://127.0.0.1:1080
export HTTPS_PROXY=socks5://127.0.0.1:1080

DNS Through SOCKS¶

Problem¶

By default, DNS queries might not go through the proxy, leaking your real location.

Browser Solution¶

Firefox: Enable "Proxy DNS when using SOCKS v5"

Chrome: Uses system DNS by default

Command Line Tools¶

# curl (built-in SOCKS support with DNS)
curl --socks5-hostname 127.0.0.1:1080 https://ifconfig.me

# wget (doesn't support SOCKS natively, use proxychains)
proxychains wget https://example.com

Proxychains¶

Route any program through the SOCKS proxy.

Install¶

apt install proxychains-ng

Configure¶

# /etc/proxychains4.conf
strict_chain
proxy_dns
tcp_read_time_out 15000
tcp_connect_time_out 8000

[ProxyList]
socks5 127.0.0.1 1080

Usage¶

# Any command
proxychains curl https://ifconfig.me
proxychains nmap -sT -p 80 target.com
proxychains wget https://example.com

SOCKS4 vs SOCKS5¶

Feature	SOCKS4	SOCKS5
TCP	Yes	Yes
UDP	No	Yes
IPv6	No	Yes
Authentication	No	Yes
DNS via proxy	No	Yes

SSH creates a SOCKS5 proxy.

SSH Config¶

# ~/.ssh/config
Host proxy
    HostName server.example.com
    User admin
    DynamicForward 1080
    Compression yes

Usage:

ssh proxy
# SOCKS proxy on :1080 while connected

Multiple Proxies¶

Multiple Servers¶

# Proxy 1
ssh -D 1080 user@server1.example.com

# Proxy 2 (different terminal)
ssh -D 1081 user@server2.example.com

Chain Through Jump Host¶

ssh -J jumphost -D 1080 user@internal.example.com

Common Use Cases¶

Secure Browsing on Public WiFi¶

ssh -D 1080 -C user@home-server.example.com
# Configure browser to use SOCKS proxy
# All traffic encrypted to your home server

Access Geo-Restricted Content¶

# Connect to server in desired country
ssh -D 1080 user@us-server.example.com
# Browse as if from that country

Access Internal Resources¶

ssh -D 1080 user@office-server.example.com
# Browser can now access internal.company.com

Scanning Through Proxy¶

ssh -D 1080 user@server.example.com

# In another terminal
proxychains nmap -sT -Pn -p 80,443 internal-target.com

API Testing from Different IP¶

ssh -D 1080 user@server.example.com

curl --socks5-hostname 127.0.0.1:1080 https://api.example.com/endpoint

Persistent SOCKS Proxy¶

Using autossh¶

autossh -M 0 -f -N -D 1080 \
    -o "ServerAliveInterval=30" \
    -o "ServerAliveCountMax=3" \
    user@server.example.com

Systemd Service¶

# /etc/systemd/system/socks-proxy.service
[Unit]
Description=SOCKS Proxy via SSH
After=network.target

[Service]
User=youruser
ExecStart=/usr/bin/ssh -N -D 127.0.0.1:1080 \
    -o ServerAliveInterval=60 \
    -o ExitOnForwardFailure=yes \
    user@server.example.com
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Performance Options¶

Enable Compression¶

ssh -D 1080 -C user@server.example.com

Faster Cipher (If CPU-Limited)¶

ssh -D 1080 -c aes128-gcm@openssh.com user@server.example.com

Verify Proxy is Working¶

Check External IP¶

# Without proxy
curl https://ifconfig.me

# With proxy
curl --socks5-hostname 127.0.0.1:1080 https://ifconfig.me

Check DNS¶

# Should show SSH server's DNS
curl --socks5-hostname 127.0.0.1:1080 https://dnsleaktest.com/

Troubleshooting¶

Proxy Not Working¶

# Check SSH tunnel is active
ss -tlnp | grep 1080

# Check you can connect to proxy
curl --socks5 127.0.0.1:1080 http://example.com

Slow Performance¶

# Enable compression
ssh -D 1080 -C user@server.example.com

# Check server bandwidth
# Your speed is limited by the SSH server's connection

DNS Leaking¶

# Ensure DNS goes through proxy
# Firefox: Enable "Proxy DNS"
# curl: Use --socks5-hostname not --socks5

Connection Drops¶

# Add keep-alive
ssh -D 1080 -o ServerAliveInterval=60 user@server.example.com

# Use autossh for auto-reconnect

Security Notes¶

Traffic visible at exit: The SSH server sees unencrypted HTTP traffic
Server logs: The server can log your browsing
HTTPS recommended: Use HTTPS sites for end-to-end encryption
Trust your server: Only use servers you control or trust
Not a VPN: Only TCP traffic, no system-wide routing

Comparison¶

Tool	Encryption	All Apps	Easy Setup	Speed
SSH SOCKS	Yes	Manual	Yes	Good
VPN	Yes	Yes	Medium	Good
Tor	Yes	Manual	Yes	Slow
Commercial proxy	Varies	Manual	Yes	Varies