What are the benefits and drawbacks of layer 2 and layer 3 VPN bridging?

1 Layer 2 VPN bridging

Layer 2 VPN bridging operates at the data link layer of the OSI model, which is responsible for transferring data between adjacent nodes on a network. Layer 2 VPN bridging creates a virtual Ethernet switch that connects devices on different networks as if they were on the same LAN. This allows devices to use their native protocols and addresses, and to broadcast and multicast traffic. Layer 2 VPN bridging is useful for applications that require low latency, high performance, or seamless integration, such as voice over IP, video conferencing, or network virtualization.

However, layer 2 VPN bridging also has some disadvantages, such as scalability, security, and complexity. Layer 2 VPN bridging can consume more bandwidth and resources than layer 3 VPN bridging, because it has to carry all the traffic from the source network, including unnecessary or unwanted packets. Layer 2 VPN bridging also exposes more information about the source network, such as MAC addresses, VLAN tags, or ARP requests, which can pose a security risk or cause conflicts. Layer 2 VPN bridging also requires more configuration and management, because it has to handle issues such as loop prevention, spanning tree protocol, or MAC address learning.

2 Layer 3 VPN bridging

Layer 3 VPN bridging operates at the network layer of the OSI model, which is responsible for routing data between different networks. Layer 3 VPN bridging creates a virtual router that connects devices on different networks as if they were on the same WAN. This allows devices to use different protocols and addresses, and to filter and optimize traffic. Layer 3 VPN bridging is useful for applications that require scalability, security, or flexibility, such as internet access, site-to-site connectivity, or network segmentation.

However, layer 3 VPN bridging also has some drawbacks, such as compatibility, performance, and overhead. Layer 3 VPN bridging can limit the functionality of some applications that rely on layer 2 features, such as broadcast and multicast traffic, VLAN tags, or MAC addresses. Layer 3 VPN bridging can also introduce some latency and degradation in the quality of service, because it has to encapsulate and decapsulate packets, perform encryption and decryption, and apply routing and filtering rules. Layer 3 VPN bridging also adds some overhead to the packets, because it has to include additional headers and trailers for the VPN tunnel.

3 How to choose the best option

When deciding which type of VPN bridging is better for a given scenario, there is no single answer; however, some guidelines can be used to inform the decision. Factors such as the size and topology of networks to bridge, the type and volume of traffic to transmit, desired security and privacy levels, performance and quality of service expectations, budget and resources available, and ease and flexibility of configuration and management should all be taken into account. Generally speaking, layer 2 VPN bridging is best for extending a LAN across different locations or for applications that need layer 2 features. On the other hand, layer 3 VPN bridging is preferable for connecting networks with different protocols or addresses or for applications that need layer 3 features.