Teleport - Secure Port Forwarding

Teleport is a secure port forwarding tool that allows you to forward ports between different instances with end-to-end encryption.

Features

• Secure Encryption: All traffic is encrypted using AES-GCM encryption with PBKDF2 key derivation
• Port Forwarding: Forward multiple ports with different protocols (TCP and UDP)
• Configuration-based: Easy configuration via YAML files
• Bidirectional: Full bidirectional port forwarding
• Keep-alive: Connection keep-alive support
• Protocol Support: Both TCP and UDP protocols supported
• Multi-Client Support: Multiple clients can connect to one server using packet tagging
• UDP Packet Tagging: UDP packets are tagged with client IDs for proper routing
• Built-in DNS Server: Custom DNS server with configurable records and backup fallback
• Rate Limiting: Configurable rate limiting with token bucket algorithm
• Connection Pooling: Efficient connection management with pooling
• Replay Protection: UDP packet replay attack protection with timestamp validation
• Advanced Logging: Sanitized logging with configurable levels, formats, and file output
• Security Features: Entropy validation, packet timestamp validation, and secure key generation

Installation

# Build the application
go build -o teleport cmd/teleport/main.go

# Or use the pre-built binaries from releases
# Windows: teleport.exe (no console) or teleport-console.exe (with console)
# Linux: teleport

Configuration

Teleport uses YAML configuration files. You need separate configurations for server and client instances.

Generate Example Configuration

Generate example configuration files:

# Generate server configuration (filename contains "server")
./teleport --generate-config --config server.yaml

# Generate client configuration  
./teleport --generate-config --config client.yaml

# Generate default configuration (client)
./teleport --generate-config

Server Configuration (server.yaml)

instance_id: teleport-server-01
listen_address: :8080
remote_address: ""
ports:
  - "tcp://localhost:80"
encryption_key: your-secure-encryption-key-change-this-to-something-random
keep_alive: true
read_timeout: 30s
write_timeout: 30s
max_connections: 1000
rate_limit:
  enabled: true
  requests_per_second: 100
  burst_size: 200
  window_size: 1s
dns_server:
  enabled: false
  listen_port: 5353
  backup_server: 8.8.8.8:53
  custom_records: []

Client Configuration (client.yaml)

instance_id: teleport-client-01
listen_address: ""
remote_address: localhost:8080
ports:
  - "tcp://80:8080"
encryption_key: your-secure-encryption-key-change-this-to-something-random
keep_alive: true
read_timeout: 30s
write_timeout: 30s
max_connections: 100
rate_limit:
  enabled: true
  requests_per_second: 50
  burst_size: 100
  window_size: 1s
dns_server:
  enabled: false
  listen_port: 5353
  backup_server: 8.8.8.8:53
  custom_records:
    - name: app.local
      type: A
      value: 127.0.0.1
      ttl: 300

Configuration Fields

• instance_id: Unique identifier for this teleport instance
• listen_address: Address to listen on (server mode) - format: host:port
• remote_address: Address of remote teleport server (client mode) - format: host:port
• ports: Array of port forwarding rules in URL-style format
  • Server format: protocol://target:targetport - forwards to remote target
  • Client format: protocol://targetport:localport - forwards to teleport server's targetport, listens on localport
  • Examples:
    • "tcp://localhost:80" (server) - listen on port 80, forward to localhost:80
    • "tcp://server-a:22" (server) - listen on port 22, forward to server-a:22
    • "tcp://80:8080" (client) - listen on port 8080, forward to teleport server's port 80
    • "udp://53:5353" (client) - listen on port 5353, forward to teleport server's port 53
• encryption_key: Shared secret key for encryption (must be the same on both sides)
• keep_alive: Enable TCP keep-alive
• read_timeout: Read timeout duration
• write_timeout: Write timeout duration
• max_connections: Maximum concurrent connections (default: 1000 for server, 100 for client)
• rate_limit: Rate limiting configuration
  • enabled: Enable rate limiting
  • requests_per_second: Maximum requests per second
  • burst_size: Maximum burst size
  • window_size: Time window for rate limiting
• dns_server: DNS server configuration
  • enabled: Enable built-in DNS server
  • listen_port: Port for DNS server to listen on
  • backup_server: Backup DNS server for fallback (e.g., "8.8.8.8:53")
  • custom_records: Array of custom DNS records
    • name: Domain name (e.g., "example.com")
    • type: Record type ("A", "AAAA", "CNAME", "MX", "TXT", "SRV", "NS")
    • value: Record value (IP address, domain name, or text)
    • ttl: Time to live in seconds
    • priority: Priority for MX and SRV records (optional)
    • weight: Weight for SRV records (optional)
    • port: Port for SRV records (optional)

Quick Start

1. Generate a secure encryption key:

   ./teleport --generate-key
   

2. Generate configuration files:

   ./teleport --generate-config --config server.yaml
   ./teleport --generate-config --config client.yaml
   

3. Edit the configs and replace the encryption key with the one you generated

4. Start the server:

   ./teleport --config server.yaml
   

5. Start the client:

   ./teleport --config client.yaml
   

Usage

Start Server

./teleport --config server.yaml

Start Client

./teleport --config client.yaml

Show Version

./teleport --version
# or
./teleport -v

Generate Random Encryption Key

./teleport --generate-key
# or
./teleport -k

This generates a cryptographically secure 256-bit encryption key that you can use in your configuration files.

Logging Options

# Set log level (debug, info, warn, error)
./teleport --config config.yaml --log-level debug

# Set log format (text, json)
./teleport --config config.yaml --log-format json

# Set log file
./teleport --config config.yaml --log-file /var/log/teleport.log

Port Format

Teleport uses URL-style port mapping format for cleaner configuration:

ports:
  - "tcp://80:8080"    # Listen on port 8080, forward to teleport server's port 80
  - "udp://53:5353"    # Listen on port 5353, forward to teleport server's port 53
  - "tcp://22:2222"    # Listen on port 2222, forward to teleport server's port 22

Format:

• Server: "protocol://target:targetport" - listen on targetport, forward to target:targetport
• Client: "protocol://targetport:localport" - listen on localport, forward to teleport server's targetport

Examples:

# Server configurations
ports:
  - "tcp://localhost:80"        # Listen on port 80, forward to localhost:80
  - "tcp://server-a:22"         # Listen on port 22, forward to server-a:22
  - "udp://dns-server:53"       # Listen on port 53, forward to dns-server:53

# Client configurations  
ports:
  - "tcp://80:8080"             # Listen on port 8080, forward to teleport server's port 80
  - "tcp://22:2222"             # Listen on port 2222, forward to teleport server's port 22
  - "udp://53:5353"             # Listen on port 5353, forward to teleport server's port 53

Example: Remote SSH Access To access SSH on Server A through teleport server on Server B:

Server B configuration:

instance_id: teleport-server-b
listen_address: :8080
remote_address: ""
ports:
  - "tcp://server-a:22"  # Listen on port 22, forward to server-a:22
encryption_key: your-shared-key

Client C configuration:

instance_id: teleport-client-c
listen_address: ""
remote_address: server-b:8080
ports:
  - "tcp://22:2222"  # Listen on local port 2222, forward to teleport server's port 22
encryption_key: your-shared-key

Then connect from Client C: ssh user@localhost -p 2222

Configuration-Based Mode Detection

The mode (server or client) is automatically determined from the configuration:

• Server Mode: When listen_address is set and remote_address is empty
• Client Mode: When remote_address is set and listen_address is empty

Important: The configuration must be clearly either a server or client - you cannot have both listen_address and remote_address set, and you must have at least one of them set.

Configuration Validation

The program validates your configuration and will show clear error messages if:

• Both addresses set: You have both listen_address and remote_address configured
• Neither address set: You have neither listen_address nor remote_address configured

Valid Server Configuration:

listen_address: :8080
remote_address: ""
ports:
  - "tcp://localhost:22"

Valid Client Configuration:

listen_address: ""
remote_address: server:8080
ports:
  - "tcp://22:2222"

Security

• All traffic is encrypted using AES-GCM encryption with PBKDF2 key derivation
• The encryption key is derived from the provided key using PBKDF2 with 100,000 iterations
• Each connection uses a unique nonce for encryption
• Connection authentication is implicit through successful decryption
• UDP packets include replay protection with timestamp validation
• Encryption keys are validated for entropy and strength
• Logging includes automatic sanitization of sensitive data
• Rate limiting prevents abuse and DoS attacks

Example Use Cases

1. SSH Tunneling: Forward SSH connections through a secure tunnel
2. Database Access: Securely access remote databases
3. Web Services: Forward HTTP/HTTPS traffic
4. DNS Services: Forward DNS queries (UDP port 53)
5. NTP Services: Forward time synchronization (UDP port 123)
6. SNMP Monitoring: Forward SNMP queries (UDP port 161)
7. Custom Services: Forward any TCP or UDP-based service
8. Local DNS Resolution: Serve custom DNS records for local development
9. DNS Override: Override specific domains with custom IP addresses
10. Service Discovery: Use SRV records for service discovery and load balancing

Example Setup

1. Server Side (where services are running):

   • Generate: ./teleport -generate-config -config teleport-server.yaml
   • Edit the configuration file with the services you want to expose
   • Run: ./teleport -config teleport-server.yaml

2. Client Side (where you want to access services):

   • Generate: ./teleport -generate-config -config teleport-client.yaml
   • Edit the configuration file with local ports and remote server address
   • Run: ./teleport -config teleport-client.yaml
   • Connect to localhost:local_port to access the remote service

Multi-Client Support

Multiple clients can connect to the same server using packet tagging:

1. Start Server: ./teleport -config teleport-server.yaml
2. Start Client 1: ./teleport -config teleport-client.yaml
3. Start Client 2: ./teleport -config teleport-client2.yaml

Both clients can use the same local ports (e.g., 5353 for DNS) because:

• Each client has a unique instance_id in their config
• UDP packets are tagged with the client ID
• Server routes responses back to the correct client
• No port conflicts between multiple clients

DNS Server Features

The built-in DNS server provides:

Custom DNS Records

• A Records: Map domain names to IPv4 addresses
• AAAA Records: Map domain names to IPv6 addresses
• CNAME Records: Create domain aliases
• MX Records: Mail server configuration
• TXT Records: Text-based records
• SRV Records: Service discovery records
• NS Records: Name server records

Example DNS Configuration

dns_server:
  enabled: true
  listen_port: 5353
  backup_server: 8.8.8.8:53
  custom_records:
    - name: api.local
      type: A
      value: 192.168.1.100
      ttl: 300
    - name: www.local
      type: CNAME
      value: api.local
      ttl: 300
    - name: _http._tcp.api.local
      type: SRV
      value: api.local
      ttl: 300
      priority: 10
      weight: 5
      port: 8080
    - name: _mysql._tcp.db.local
      type: SRV
      value: db.local
      ttl: 300
      priority: 10
      weight: 1
      port: 3306

DNS Usage

# Test custom DNS records
nslookup api.local localhost -port=5353
nslookup www.local localhost -port=5353

# Test SRV records for service discovery
nslookup -type=SRV _http._tcp.api.local localhost -port=5353
nslookup -type=SRV _mysql._tcp.db.local localhost -port=5353

# Fallback to backup server for unknown domains
nslookup google.com localhost -port=5353

Binary Names

The application provides different binaries for different use cases:

• teleport: Main binary (Windows: no console window, Linux: standard)
• teleport-console: Console version (Windows: shows console window)

Advanced Features

Rate Limiting

Teleport includes configurable rate limiting to prevent abuse:

rate_limit:
  enabled: true
  requests_per_second: 100  # Maximum requests per second
  burst_size: 200          # Maximum burst size
  window_size: 1s          # Time window for rate limiting

Advanced Logging

Teleport includes sophisticated logging with:

• Configurable log levels (debug, info, warn, error)
• Multiple output formats (text, JSON)
• File and console output support
• Automatic sanitization of sensitive data (keys, passwords, tokens)
• Secure file permissions (owner read/write only)

Connection Management

• Connection Pooling: Efficient connection reuse for better performance
• Connection Limits: Configurable maximum concurrent connections
• Health Checks: Automatic detection and cleanup of dead connections
• Graceful Shutdown: Proper cleanup of resources on exit

Notes

• The encryption key must be identical on both server and client
• Use ./teleport --generate-key to create a secure random encryption key
• The server listens on the specified listen_address for incoming connections
• The client connects to the remote server and forwards local connections
• All port forwarding is bidirectional
• Port format uses URL-style conventions: "protocol://target:port"
• Configuration files use YAML format for better readability
• The application automatically detects server vs client mode based on configuration
• UDP packets include replay protection and timestamp validation
• All sensitive data in logs is automatically sanitized
• Rate limiting helps prevent abuse and DoS attacks
• Connection pooling improves performance for high-traffic scenarios