VPN tunneling is the core mechanism of VPN, which creates virtual private channels over public networks to transmit data. Tunneling technology involves the processes of data encapsulation, transmission, and decapsulation.
Working principle of VPN tunneling:
-
Data Encapsulation
- Original data packets are added with new header information
- New headers contain tunnel endpoint address information
- The entire original packet becomes the payload of the new packet
-
Tunnel Establishment
- Client and server negotiate tunnel parameters
- Establish secure connection channel
- Configure encryption and authentication parameters
-
Data Transmission
- Encapsulated packets are transmitted over public networks
- Intermediate routers can only see the outer header
- Data content is protected by encryption
-
Data Decapsulation
- Receiver removes the outer header
- Decrypts data content
- Extracts original data packet
Common tunneling technologies:
-
PPTP Tunneling
- Uses GRE protocol to encapsulate PPP frames
- Control port 1723, uses TCP
- Data transmission uses GRE protocol
-
L2TP Tunneling
- Uses UDP to encapsulate PPP frames
- Port 1701
- Usually combined with IPsec to provide encryption
-
IPsec Tunnel Mode
- Encapsulates entire IP packets
- Adds new IP header
- Provides end-to-end security protection
-
OpenVPN Tunneling
- Uses TLS/SSL protocol
- Configurable TCP or UDP
- Flexible port selection
Advantages of tunneling technology:
- Hides internal network structure
- Transmits private network addresses
- Crosses insecure public networks
- Supports multiple network protocols
Challenges of tunneling technology:
- Increases packet size (MTU issues)
- Adds network latency
- Needs to handle NAT traversal
- Relatively complex configuration