BGP Interview Questions

BGP Interview questions and answers are shared here. In this post, we will look at some of the important BGP questions that are asked in the Interviews and some of the certification exams. You can consider this as a BGP Quiz and test your BGP knowledge.

Which of the below option is the reason to run IBGP? (Choose Two)

A. It is used for the reachability between PE devices in the MPLS network B. It is used to carry EBGP prefixes inside an Autonomous System C. It is used with Route Reflectors for the scalability reason in large scale networks D. It is used to prevent failures outside your network from impacting your internal network operation

Answer: One of the correct answers to this question is to carry EBGP prefixes inside an Autonomous system. IGP is used for the reachability between PE devices in an MPLS network. Option C is valid but not the correct answer, because; the question is asking about the reasons, not the best practices. Option D is one of the correct answers as well because, with IBGP, the internal network is protected from outside failures by separating the local failure domains. That’s why; the answers to this question are B and D.

Which of the below options are true for the BGP Route Reflectors? (Choose Three)

A. Route Reflectors provide scalability in large scale network design B. Route Reflectors hide the available paths C. Route Reflectors selects and advertise only the best path to Route Reflector clients D. Route Reflectors can be placed anywhere in the IP backbone as an IPv4 RR

Answer: Route reflectors are used to improve the scalability of the BGP design in large-scale deployments. BGP Route reflectors hide the available path information by selecting and advertising only the best path to the clients. Thus the correct answer to this question is A, B, and C. Option D is wrong because Route Reflectors should follow the physical topology in an IP backbone, they cannot be placed everywhere, and careful planning is required. An otherwise forwarding loop occurs.

Which below attributes are commonly used for BGP path manipulation? (Choose Three)

A. Local Preference B. Origin C. As-Path D. Community E. Weight Answer: Origin is not used commonly for the BGP path manipulation. Weight is Cisco preparatory and it is only local to the routers. It shouldn’t be used for path manipulation.

The answer to this question is A, C, and D.

Which of the below options is used in the Public Internet Exchange Points to reduce configuration overhead on the BGP devices?

A. BGP Route Reflectors B. BGP Prefix Lists C. BGP Route Servers D. BGP Map Servers

Answer: There is nothing called BGP Map-Servers. In the Public Internet Exchange points, BGP Route Servers are used to reduce configuration overhead. They improve scalability. Very similar to Route Reflectors but Route Reflectors are used in IBGP, not in the Public Exchange Points. That’s why the answer to this question is C.

Which below options are true for the BGP Confederation? (Choose Three)

A. It is done by creating a Sub-autonomous system B. It is easier to migrate from full-mesh IBGP, compare to BGP Route Reflectors C. Between Sub Autonomous Systems mostly EBGP rules apply D. Compared to BGP Route Reflector design, it is less commonly deployed in the networks

Answer: From the migration point of view, Full mesh IBGP to BGP Confederation is harder, compared to BGP Route Reflectors. Thus Option B is invalid. All the other options are correct thus the answer to this question is A, C, and D

Which below option is used for inbound BGP path manipulation? (Choose Three)

A. Local Preference B. MED C. As-Path prepending D. Community E. Hot Potato Routing

Answer: Hot Potato Routing and Local Preference are used for Outbound BGP Path manipulation. BGP MED attribute should be used if there is only one upstream ISP but still it is used for inbound path manipulation. AS-Path prepending and the communities are used for the multihoming connections as well.

That’s why; the answer to this question is B, C, and D.

What does MP-BGP (Multi-Protocol BGP) mean?

A. BGP implementation which can converge in less than a second B. BGP implementation which is used in Service Provider networks C. BGP implementation which can carry multiple BGP Address Families D. BGP implementation which is used in Enterprise Networks

Answer: MP-BGP (Multi-Protocol BGP) is the BGP implementation, which can carry multiple Address Families. BGP in 2016, can carry more than 20 different Address Families such as IPv4 Unicast, IPv6 Unicast, IPv4 Multicast, L2 VPN, L3VPN, Flowspecand so on. That’s; why; the answer to this question is C.

What does Hot Potato Routing mean?

A. Sending the traffic to the most optimum exit for the neighboring AS B. Sending the traffic to the closest exit to the neighboring AS C. By coordinating with the neighboring AS, sending traffic to the closest exit point D. It is the other name of BGP Multipath Answer: Hot Potato Routing means, sending the traffic to the closest exit point from the Local Autonomous system to the neighboring Autonomous System by taking the IGP metric into consideration. There is no coordination between the Autonomous System in Hot Potato Routing definition. But Coordination with the Hot Potato Routing case study was provided in the BGP Zero to Hero Course. That’s why; the answer to this question is B

Fictitious Service Provider is considering providing an availability SLA for their MPLS VPN customers. They want to provide sub-second convergence in case of link or node failure scenarios. What would you suggest to this company to achieve its goal? (Choose Two)

A. Implementing BFD B. Implementing BGP PIC Core and Edge C. Implementing BGP Route Reflectors D. Implementing IGP FRR

Answer: They should implement BGP PIC features to protect BGP from link or node failure. Especially Edge node failures, even if MPLS Traffic Engineering or IP FRR deployed, couldn’t be recovered in a sub-second. Since BGP PIC convergence mostly depends on IGP convergence as well, deploying IGP FRR (Fast Reroute) provides the necessary infrastructure for the BGP PIC. They should be deployed together. BFD is just a failure detection mechanism. IGP Convergence depends on many other parameters tuningThat’s why; the answer to this question is B and D

With which below options, the internal BGP speaker can receive more than one best path even if BGP Route Reflectors are deployed? (Choose Three)

A. BGP Shadow RR B. BGP Shadow Sessions C. BGP Add-path D. BGP Confederation E. BGP Multipath

Answer: BGP Shadow Sessions, BGP Shadow RR, and BGP Add-path design provide more than the best path to the internal BGP speaker even if BGP Route Reflectors are deployed. BGP Multipath requires more than one best path and all the path attributes to be the same. Thus it requires one of the above mechanisms. BGP Confederation doesn’t provide this functionality. That’s why; the answer to this question is A, B, and C.

Which below option is recommended to send more than one best path to the VPN PEs in the MPLS VPN deployment if VPN Route Reflectors are deployed?

A. BGP Add-path B. BGP Shadow RR C. BGP Full Mesh D. Unique RD per VRF per PE

Answer: BGP Add-path, BGP Shadow RR, and Sessions deployments are suitable for the IP backbones. If there is an MPLS backbone, configuring unique RD per VRF per PE is the best and recommended design option since there is no software or hardware upgrade, no additional BGP sessions, and so on. That’s why the answer to this question is D

What are the reasons to send more than one BGP best path in IP and MPLS deployment? (Choose Four)

A. BGP Multipath B. BGP Fast Reroute C. BGP Multihop D. Preventing Routing Oscillation E. Optimal BGP routing

Answer: There are many reasons to send more than one BGP best path in both IP and MPLS deployments. These are; avoiding routing oscillations, BGP Multipathing, Fast convergence/Fast Reroute, and Optimal Routing. Sometimes for optimal routing, just sending more than one BGP best path is not enough but may require all available paths though. That’s why, the answer to this question is A, B, D, and E

What is the drawback of sending more than one BGP best path in BGP?

A. More resource usage B. Sub Optimal Routing C. Slower Convergence D. Security Risk Answer: Sending more than one BGP best path requires more memory, CPU, and network bandwidth, thus more resource usage in the network. As a rule of thumb, whenever more information is sent, it consumes more resources and may provide optimal routing, better high availability, and better convergence. All other options are wrong, except Option A

What below options are the advantages of the Full Mesh IBGP design compare to BGP Route Reflector design? (Choose Four)

A. It can provide more optimal routing compared to Route Reflector design B. It can provide faster routing convergence compared to Route Reflector design C. It provides better resource usage compared to the Route Reflector design D. It can provide better protection against route churn E. Multipath information is difficult to propagate in a route reflector topologies

Answer: Although there are advantages of using BGP Route Reflectors, there are many drawbacks as well. Probably it is more harmful than deploying Full Mesh IBGP if the requirement is optimal routing, faster convergence, and avoiding route churns. Sending multiple paths is difficult since it requires Shadow Sessions, RR, or Add-path deployments in Route Reflector topologies. Full Mesh IBGP design consumes more device and network resources and requires more configurations on the devices compared to Route Reflector design. That’s why the answer to this question is A, B, D, and E

Which below options are true for the BGP PIC deployment? (Choose Two)

A. BGP PIC can provide sub-second convergence even if there are millions of prefixes in the routing table B. BGP edge devices don’t have to receive more than one best path for BGP PIC Edge to work C. BGP PIC Edge can protect both from Edge link and Node failure D. BGP PIC has to work with BGP Add-Path

Answer: BGP edge nodes have to receive more than one best path for BGP PIC Edge operation. This was explained in the BGP chapter in detail. BGP Add-Path is one of the mechanisms, which is used to send multiple paths even if RR is deployed in the network. But BGP Add-Path is not mandatory for BGP PIC. BGP PIC Edge can protect from both Edge link and node failures and can provide sub-second convergence even if there are millions of prefixes. That’s why the correct answer to this question is A and C These are some of the BGP Interview Questions we encounter in real life, if you would like to see more BGP interview questions, please let us know. You can share this post if you would like to see more BGP Interview Questions or BGP certification exam questions and the answers.

In the below topology there are two data centers of the Service Provider. If the requirement were to provide the closest exit for the Route Reflector clients, in which data center would you deploy the Route Reflectors?

A. In West DC B. In East DC C. Doesn’t matter the placement D. Both in East and West DC

Answer: Route Reflectors should be placed in both East and West DC. Otherwise, Route Reflector would choose the best path from their point of view and would send the best path to the Route Reflector Clients from their best path. If RR would be placed in West DC, all BGP RR Clients in East DC would choose the West DC IGW (Internet Gateways) as the exit point and vice versa. Thus the correct answer to this question is D

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