20 Layer 2 VPN Interview Questions and Answers

Layer 2 VPNs are a type of Virtual Private Network (VPN) that uses MPLS labels to route traffic between sites. They are commonly used by businesses to connect their offices together or to connect to their customers and partners. If you are interviewing for a position that involves Layer 2 VPNs, you should be prepared to answer questions about your experience and knowledge. In this article, we will review some common Layer 2 VPN interview questions and provide some tips on how to answer them.

Layer 2 VPN Interview Questions and Answers

Here are 20 commonly asked Layer 2 VPN interview questions and answers to prepare you for your interview:

1. What is a Layer 2 VPN?

A Layer 2 VPN is a type of VPN that uses a layer 2 network to connect remote sites or users together. A layer 2 network is a network that uses switches and bridges to connect devices together. A Layer 2 VPN can be used to connect two or more sites together or to connect two or more users together.

2. Why would you use a layer 2 VPN instead of a traditional multipoint-to-multipoint network model?

Layer 2 VPNs offer a number of advantages over traditional multipoint-to-multipoint network models. One advantage is that layer 2 VPNs can provide a more secure connection since they encrypt all data that is sent across the VPN. Additionally, layer 2 VPNs can be more scalable since they can be easily added to an existing network without the need to reconfigure the entire network.

3. Can you explain how an MPLS L2VPN works?

MPLS L2VPNs work by creating a “tunnel” between two customer edge (CE) devices. This tunnel is created by tagging each packet with a label, which is then used to route the packet through the network. The tunnel ensures that the packets are delivered in the correct order and prevents them from being dropped or reordered.

4. How does a VPLS work?

A VPLS is a layer 2 VPN that uses MPLS to provide a switched Ethernet service. It is similar to a VLAN in that it allows multiple devices to be connected together as if they were on the same LAN, but it uses MPLS to provide a more scalable solution.

5. What are the differences between an EoMPLS and a VPLS solution?

EoMPLS is a Layer 2 VPN solution that uses MPLS to provide a point-to-point connection between two sites. VPLS is a Layer 2 VPN solution that uses MPLS to provide a point-to-multipoint connection between multiple sites.

6. What’s the difference between an EVPN and a VPLS service?

An EVPN is a Layer 2 VPN service that uses Ethernet VPN technology to provide a scalable, secure, and flexible solution for interconnecting multiple sites. A VPLS is a Layer 2 VPN service that uses virtual private LAN service technology to provide a scalable and secure solution for interconnecting multiple sites.

7. What’s the purpose of the inner label in an L2VPN architecture?

The inner label is used to identify the customer site that a particular packet is destined for. This allows the service provider to route the packet to the correct customer site.

8. What is a BGP next hop self mechanism?

The BGP next hop self mechanism is a method of ensuring that traffic destined for a particular VPN will always be routed through the correct gateway. This is accomplished by advertising the VPN’s gateway address as the next hop for all routes within the VPN.

9. What do you understand about route reflectors?

A route reflector is a device that helps to distribute routing information between different devices in a network. It can be used to help improve the efficiency of routing by reducing the amount of traffic that needs to be sent between devices.

10. What do you understand about ARP suppression?

ARP suppression is a technique used in Layer 2 VPNs to help reduce the amount of broadcast traffic that is sent across the VPN. By suppressing ARP broadcasts, the VPN can operate more efficiently and with less traffic.

11. What types of services can be used with an L2VPN gateway?

L2VPN gateway services can be used for a variety of purposes, including but not limited to:

– Providing a secure connection between two or more sites
– Allowing for the creation of a virtual private network (VPN)
– Enabling the use of voice over IP (VoIP)
– Supporting video conferencing
– Allowing for the sharing of files and other data

12. What is meant by a pseudowire in context with L2VPNs?

A pseudowire is a logical connection that is used to connect two devices that would normally not be able to communicate with each other. In the context of L2VPNs, a pseudowire is used to connect two devices that are using different Layer 2 protocols. This allows the devices to communicate with each other as if they were using the same protocol.

13. What is the best way to achieve high availability when using L2VPNs?

The best way to achieve high availability when using L2VPNs is to use a combination of link aggregation and redundancy. Link aggregation will allow you to combine multiple physical links into a single logical link, which will increase your bandwidth and improve your resilience to link failures. Redundancy will provide you with a backup link in case your primary link fails.

14. Can you give me some examples of real-world applications for L2VPNs?

L2VPNs can be used for a variety of purposes, but they are most commonly used in order to connect two or more sites that are geographically separated. This can be useful for companies that have multiple locations, or for service providers that need to offer VPN services to their customers. L2VPNs can also be used to connect devices that are not on the same network, such as when connecting a laptop to a printer.

15. What are the advantages and disadvantages of using an L2VPN over an L3VPN?

The main advantage of using an L2VPN over an L3VPN is that L2VPNs can provide a simpler, more efficient, and more scalable network. L2VPNs also have the advantage of being able to support a variety of different networking protocols, making them more flexible than L3VPNs. However, L2VPNs can be more difficult to configure and manage, and they may not provide the same level of security as L3VPNs.

16. Can you explain what the acast-optimized option in Junos OS does?

The acast-optimized option in Junos OS is used to improve the performance of Layer 2 VPNs by reducing the amount of control traffic that is sent between sites. This option is particularly useful for large-scale VPNs that span multiple sites.

17. Can you explain what the mpls encapsulation command does?

The mpls encapsulation command is used to specify the encapsulation type that will be used for MPLS packets. This command can be used to specify either MPLS-TP or MPLS-UDP encapsulation.

18. What do you understand about the remote PE addresses feature in Junos?

The remote PE addresses feature in Junos allows you to configure a Layer 2 VPN to connect to multiple remote PE devices. This can be useful if you have a multi-site VPN or if you want to connect to multiple PE devices for redundancy.

19. Is it possible to configure multiple logical interfaces on top of a single physical interface? If yes, then how?

Yes, it is possible to configure multiple logical interfaces on top of a single physical interface. This can be done by creating multiple sub-interfaces, each with its own unique configuration.

20. What is a virtual circuit ID?

A virtual circuit ID is a unique identifier that is assigned to a Layer 2 VPN connection. This ID is used to identify the connection between the two VPN endpoints.