Which statement is true about the operation of Layer 2 VPNs?
Click on the arrows to vote for the correct answer
A. B. C. D.D
Layer 2 Virtual Private Networks (L2 VPNs) allow service providers to offer Layer 2 connectivity between geographically dispersed customer sites. These customer sites may be connected through a service provider network or over the internet. L2 VPNs are commonly used for applications that require transparent Layer 2 connectivity between sites such as data centers, storage area networks (SANs), and Metro Ethernet.
Now, let's evaluate each answer option and find out which statement is true about the operation of Layer 2 VPNs.
A. Layer 2 VPNs require that CE devices use the same Layer 2 encapsulation This statement is true. In L2 VPNs, the customer edge (CE) devices must use the same Layer 2 encapsulation protocol. This is because the service provider network does not perform any Layer 3 routing or forwarding, and the customer's Layer 2 frames are transported transparently across the service provider's network. If different encapsulation protocols were used on the CE devices, the frames would not be properly transported across the network.
B. Layer 2 VPNs do not permit CE devices to operate a Layer 3 protocol with each other This statement is false. L2 VPNs only transport Layer 2 frames between customer sites. CE devices can operate Layer 3 protocols between each other as long as they are not transported across the L2 VPN. However, some service providers offer Layer 3 VPNs (L3 VPNs) that allow customers to run Layer 3 protocols over the service provider's network.
C. Service provider routers must evaluate the IP header of packets as they traverse their network This statement is false. L2 VPNs are transparent to Layer 3 protocols, so service provider routers do not need to evaluate the IP header of packets as they traverse the network. The service provider's network only transports Layer 2 frames between customer sites.
D. Layer 2 VPNs allow CEs to use different encapsulations on either side of the VPN This statement is false. As mentioned in option A, CE devices must use the same Layer 2 encapsulation protocol on either side of the L2 VPN. If different encapsulation protocols were used, the frames would not be properly transported across the network.
In conclusion, option A is the correct answer. L2 VPNs require that CE devices use the same Layer 2 encapsulation protocol on either side of the VPN.