9 BGP Interview Questions (With Sample Answers To Study)

Updated 29 September 2022

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Border Gateway Protocol (BGP) is a gateway protocol that network engineers and information technology (IT) professionals may use in their work. When you apply for a technical position, a hiring manager may ask you questions about BGP to assess your knowledge and qualifications to perform the expected duties. Understanding how to answer interview questions about BGP can help you impress a hiring manager and improve your chances of obtaining an employment offer.

In this article, we provide nine BGP interview questions and sample answers that you can use to create your own responses and show your knowledge.

9 BGP Interview Questions With Sample Answers

Here are nine BGP interview questions with sample answers:

1. What is BGP?

A hiring manager may ask this question to determine your basic familiarity with BGP. Providing a straightforward answer can help you feel more confident and comfortable throughout the interview. In your response, you can offer a brief definition of BGP. Here, it's important to clarify what BGP stands for if the hiring manager does not state the full term in their question.

Example: 'BGP stands for border gateway protocol. It is the protocol responsible for analysing data that someone sends over the Internet. It analyses the data it receives and determines which path is optimal for the data to take. To select the most efficient path for data, the BGP may switch frequently between different autonomous systems.'

2. Why is BGP important?

After providing a BGP definition, a hiring manager may ask you about its importance to evaluate if you understand its benefits and role. By explaining the importance of BGP, you can show that you understand its various applications. In your answer, you can provide a simple explanation of how BGP is applicable to everyday users. Your ability to provide a simple response can show that you have a solid understanding and do not require the use of jargon to convey your idea.

Example: 'BGP is important because it is the protocol that allows users to route data over the Internet. For instance, consider an Internet user who lives in Sweden. When they visit a website, they can communicate quickly with origin servers in Australia because the protocol facilitates the communication and the transmission of data.'

3. Can you run two BGP processes on one router at the same time?

This is a situational interview question that relates to BGP. A hiring manager may ask you this question to determine how you can run BGP processes. In your response, state that this situation is not possible and briefly explain why.

Example: 'It is not possible to run two BGP processes on one router at the same time. If you want to run two BGP processes, you can use a second router. The reasoning for this is because BGP is an exterior gateway protocol rather than an interior gateway protocol.'

4. Can routers on different subnets become BGP neighbours?

A hiring manager may ask this question to assess your understanding of the industry-specific terminology subnets and neighbours, as they relate to BGP. You can begin your response by describing how IT professionals typically set up BGP. Then, you can clarify that this scenario is possible.

Example: 'IT professionals typically set up BGP between two routers. These two routers are a part of unique autonomous systems and share a direct connection. The routers do not require their neighbours to exist on the same subnet. The routers use a transmission control protocol (TCP) connection to receive and send BGP messages. This means that neighbouring routers can either be on the same subnet or different subnets.'

5. What is the hold-down timer?

A hiring manager may ask this question to determine your familiarity with how BGP can check the availability of its neighbours. In your response, provide a definition of the hold-down timer. You may also mention the keep-alive timer to show your knowledge of the various timers that relate to BGP.

Example: 'The hold-down timer refers to the amount of time that a local BGP neighbour can wait until it declares an isolated neighbour as unavailable. By default, this interval is 90 seconds. This interval is three times as long as the interval for the keep-alive timer, which checks neighbour availability every 30 seconds. If a local neighbour does not receive three keep-alive packets from an isolated neighbour for the duration of the hold-down timer, it changes the status of the neighbourship. The local neighbour also removes related routes that the neighbour from the BGP table advertises.'

6. What are some of the common BGP attributes?

A hiring manager may ask this question to determine how well you understand the metrics that dictate BGP path selection. In your response, you can mention several attributes to show that you have a solid understanding of which attributes can influence BGP path selection. A few you can consider mentioning include weight, origin code and AS path length.

Example: 'A few attributes that affect BGP path selection include weight, origin code, AS path length, router ID, neighbour IP address, router ID and the oldest available path. Another factor that may influence BGP path selection is local preference. With this attribute, the default value is always 100, but the highest local value is preferable.'

7. What are some differences between BGP and Open Shortest Path First?

A hiring manager may ask this question to evaluate your understanding of a protocol that relates to BGP, but is different in several ways. In your response, you may mention how one is a fast currency protocol, and the other is a slow currency protocol. You may also provide the differences between their port connections and implementation processes.

Example: 'Open Shortest Path First (OSPF) is a fast currency protocol and connects to port number 89. BGP is a slow currency protocol and connects to port number 179. OSPF employs the internet protocol, while BGP employs the transmission control protocol. Another key difference between OSPF and BGP is their implementation processes. BGP is typically much more challenging to implement than OSPF.'

8. What are the differences between BGP and Routing Information Protocol?

A hiring manager may want to use this question to assess your understanding of different protocol types. In your response, explain the different algorithms that both protocols use. You can also describe what metrics they use and what businesses typically implement these protocols.

Example: 'One of the main differences between BGP and Routing Information Protocol (RIP) is that BGP uses the best-path algorithm while RIP uses the Bellman-Ford algorithm. Large organisations typically use BGP, while smaller organisations use RIP. Another key difference is that BGP offers calculations in terms of hop count, while RIP offers calculations in terms of bandwidth. RIP limits the bandwidth to 15 hops, while BGP does not have any limitations in place.'

9. What different message types might you see in BGP?

Your response to this question can help a hiring manager determine how well you can interpret messages that BGP generates. In your response, you can mention a few types and briefly explain their meanings and what may happen when you receive one.

Example: 'An open message initiates the creation of a neighbour relationship. It also facilitates the exchange of parameters, such as authentication and AS values. Another type of message is the keep-alive message, which helps maintain a neighbour relationship. The update messages help with the trading of path attributes, while notification messages signal BGP errors. Upon the distribution of a notification message, the neighbour relationships reset themselves.'