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	✅	✅
UDP	❌	✅
IPv6	❌	✅
Authentication	❌	✅
DNS via proxy	❌	✅

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	✅	Manual	✅	Good
VPN	✅	✅	Medium	Good
Tor	✅	Manual	✅	Slow
Commercial proxy	Varies	Manual	✅	Varies