When attempting to establish a SOCKS proxy via SSH dynamic port forwarding with:

ssh -D localhost:8000 user@myserver -v

The connection establishes but browser requests fail with "Connection reset" errors. Wireshark shows no tunnel traffic despite successful SSH authentication.

The verbose output shows these critical messages:

debug1: Connection to port 8000 forwarding to socks port 0 requested.
debug1: channel 3: new [dynamic-tcpip]
debug1: channel 3: free: dynamic-tcpip, nchannels 4

This indicates the SSH client is attempting to create the tunnel but something is terminating the channel immediately.

1. Server Configuration Issues

Check /etc/ssh/sshd_config on the server:

# Ensure these exist:
AllowTcpForwarding yes
PermitOpen any
GatewayPorts yes

After modifying, restart SSH:

sudo systemctl restart sshd

2. Local Port Conflicts

Verify port 8000 isn't in use:

netstat -tulnp | grep 8000
lsof -i :8000

3. Firewall Interference

Check both server and local firewall rules:

# On Linux:
sudo iptables -L -n -v
# On Windows:
netsh advfirewall show allprofiles

Use curl to test the tunnel directly:

curl --socks5 localhost:8000 http://ifconfig.me

For detailed packet inspection:

sudo tcpdump -i lo -nnX port 8000

Try different binding addresses:

ssh -D 0.0.0.0:8000 user@myserver

Or use Putty configuration:

1. Connection > SSH > Tunnels
2. Add new dynamic forwarding: D8000
3. Enable "Remote ports do the same"

When debugging, always:

1. Check server logs: /var/log/auth.log
2. Test with minimal config: ssh -vvv -N -D 8000 user@host
3. Verify with alternative clients (Putty, Git Bash)
4. Test different ports (8080, 1080)

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When attempting to establish a SOCKS proxy via SSH dynamic port forwarding with:

ssh -D localhost:8000 user@myserver

The connection establishes without SSH-level errors, but browser configuration fails with "Connection has been reset". Wireshark shows no tunnel traffic despite proper SSH authentication.

The verbose SSH output reveals critical clues:

debug1: Connection to port 8000 forwarding to socks port 0 requested.
debug1: channel 3: new [dynamic-tcpip]
debug1: channel 3: free: dynamic-tcpip, nchannels 4

This indicates the SSH client is attempting but immediately closing the tunnel channel.

Network-level blockers:

• Local firewall (iptables/ufw) blocking loopback interface traffic
• Corporate network proxies interfering with SOCKS communication

SSH configuration gaps:

• Missing GatewayPorts directive when binding non-localhost interfaces
• Insufficient permissions despite AllowTcpForwarding yes

1. Validate base SSH functionality:

# Test raw SSH connection
ssh -T user@myserver "echo ConnectionVerified"

2. Check local port binding:

# Linux/MacOS
lsof -i :8000

# Windows
netstat -ano | findstr 8000

3. Test tunnel with curl:

curl --socks5 localhost:8000 http://ifconfig.me

For Linux systems:

# Monitor kernel-level connections
sudo ss -tulnp | grep 8000

# Check SELinux context
sudo ausearch -m avc | grep sshd

Windows-specific checks:

# Verify Windows Defender firewall rules
Get-NetFirewallRule | Where-Object { $_.DisplayName -like "*ssh*" }

Server-side sshd_config:

# /etc/ssh/sshd_config
AllowTcpForwarding yes
GatewayPorts clientspecified
PermitTunnel yes

Alternative connection method:

ssh -NfD 8000 user@myserver -o ExitOnForwardFailure=yes

Firefox SOCKS5 setup:

1. Navigate to about:preferences#general
2. Network Settings → Manual proxy configuration
3. Set SOCKS Host to localhost, Port 8000
4. Select SOCKS v5 and enable Proxy DNS when using SOCKS v5

Multi-hop tunneling:

ssh -L 9000:localhost:8000 jumpuser@bastion ssh -D localhost:8000 user@target

SSH config file simplification:

Host proxy-tunnel
  HostName myserver
  User user
  DynamicForward 8000
  ServerAliveInterval 60