Interview Questions.

BGP Interview Questions And Answers - Jul 16, 2022


BGP Interview Questions And Answers

Q1. What is BGP?


Ans: Border Gateway Protocol (BGP):

 is a standardized exterior gateway protocol designed to trade routing and reachability records among self reliant structures (AS) at the Internet. The protocol is assessed as a direction vector protocol. The Border Gateway Protocol makes routing decisions based on paths, community rules, or rule-sets configured by way of a network administrator and is concerned in making center routing decisions.

BGP can be used for routing inside an independent device. In this software it's far called Interior Border Gateway Protocol, Internal BGP, or iBGP. In assessment, the Internet software of the protocol can be known as Exterior Border Gateway Protocol, External BGP, or eBGP.

Q2. What is the reason of bgp ?

Ans: The essential motive of BGP is to alternate routing updates like other routing protocols, however BGP commonly does no longer trade character community routes (but it technically can), it exchanges summaries of community routes. This is because the everyday use of BGP is over very huge networks together with the Internet.

Q3. What is the Port Number of BGP?

Ans: BGP uses TCP port 179.

Q4. Can I run two BGP procedure on unmarried router?

Ans: No, You can not run two BGP process on a Single Router.

Q5.  What is a poison reverse?

Ans: poison opposite. Posted by: Margaret Rouse. In a laptop community that uses the Routing Information Protocol (RIP) or different distance vector routing protocols, a poison reverse is a way in which a gateway node tells its neighbor gateways that one of the gateways is not related.

Q6. What is the distinction among cut up horizon and poison reverse?

Ans: Split-horizon routing with poison reverse is a variant of split-horizon course advertising and marketing in which a router actively advertises routes as unreachable over the interface over which they had been found out by way of putting the route metric to infinite (sixteen for RIP).

Q7. What is rip in networking?

Ans: The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which rent the hop matter as a routing metric. RIP prevents routing loops by means of enforcing a restrict at the variety of hops allowed in a course from source to vacation spot.

Q8. Can I use BGP rather than any IGP?

Ans: No, because bgp works among autonomous structures but igp works internal of autonomous structures.

Q9. What is route reflector and why it's far required?

Ans: A course reflector is BGP router this is allowed to break the iBGP loop avoidance rule. Route reflectors can market it updates received from an iBGP peer to every other iBGP peer below specific conditions.

By breaking the guidelines, course reflectors are used to do away with the full mesh requirement and allow for constructing iBGP networks that scale effortlessly and cleanly.

Q10. What is the BGP route choice criteria?

Ans: BGP attempts to slim its direction choice down to one nice route; it does no longer load stability by means of default. To do so, it examines the course attributes of any loop-free, synchronized (if synchronization is enabled) routes with a available subsequent-hop within the following order:

Choose the course with the very best weight.

If weight isn't set, select the direction with the very best local preference.

Choose routes that this router originated.

Choose the path with the shortest Autonomous System route.

Choose the path with the lowest origin code (i is lowest, e is subsequent, ? Is closing).

Choose the route with the bottom MED, if the same Autonomous System advertises the viable routes.

Choose an EBGP direction over an IBGP course.

Choose the path thru the closest IGP neighbor as determined by means of the bottom IGP metric.

Choose the oldest course

Choose a path via the neighbor with the bottom router ID.

Choose a course via the neighbor with the bottom IP cope with.

Q11. What codecs can I use to configure the BGP community characteristic?

Ans: In Cisco IOS® Software Release 12.Zero and later, you could configure communities in 3 specific codecs referred to as decimal, hexadecimal, and AA:NN. By default, Cisco IOS uses the older decimal layout. In order to configure and display in AA:NN, in which the first part is the AS wide variety and the second part is a 2-byte number, problem the ip bgp-community new-format global configuration command.

Q12. What are the most not unusual distance vector routing protocols?

Ans: Distance Vector Routing Definition: Distance vector routing is a simple routing protocol utilized in packet-switched networks that makes use of distance to decide the satisfactory packet forwarding direction. ... A hop is the ride that a packet takes from one router to another because it traverses a network at the manner to its destination.

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Q13. What is recursive lookup in BGP and the way it works?

Ans: The router appears up the BGP direction and the BGP subsequent hop to reach a destination in the far flung AS. Then the router appears up the direction to reach the BGP subsequent hop the usage of the IGP.

Q14. What is an autonomous gadget (AS) wide variety and the way do I attain one?

Ans: AS numbers are globally precise numbers that are used to pick out ASes, and which allow an AS to alternate exterior routing information among neighboring ASes. An AS is a related institution of IP networks that adhere to a single and absolutely described routing coverage.

There are a limited number of available AS numbers. Therefore, it is critical to determine which sites require unique AS numbers and which do now not. Sites that do not require a unique AS variety should use one or greater of the AS numbers reserved for private use, which can be in the variety from 64512 to 65535. Access the AS Number Registration Services website to gain an AS variety.

Q15. Define various BGP direction attributes.

Ans: BGP chooses a course to a community based totally at the attributes of its route. Four classes of attributes exist as follows:

Well-acknowledged mandatory: Must be diagnosed through all BGP routers, present in all BGP updates, and surpassed directly to other BGP routers. For example, AS route, starting place, and next hop.

Well-known discretionary: Must be diagnosed through all BGP routers and surpassed directly to different BGP routers however want not be found in an update, as an example, neighborhood preference.

Optional transitive: Might or might not be identified with the aid of a BGP router but is surpassed on to different BGP routers. If not identified, it is marked as partial, for example, aggregator, network.

Optional nontransitive: Might or won't be recognized by using a BGP router and isn't passed on to different routers, for example, Multi-Exit Discriminator (MED), originator ID.

Q16. What does a next hop of 0.0.Zero.0 imply in the show ip bgp command output?

Ans: A community in the BGP table with a next hop deal with of 0.Zero.0.Zero way that the network is regionally originated through redistribution of Interior Gateway Protocol (IGP) into BGP, or through a network or combination command inside the BGP configuration.

Q17. What is synchronization, and the way does it have an effect on BGP routes mounted in the IP routing desk?

Ans: If your AS passes visitors from some other AS to a 3rd AS, BGP ought to not put it up for sale a path earlier than all routers to your AS find out about the route through IGP. BGP waits till IGP propagates the course inside the AS after which advertises it to external peers. A BGP router with synchronization enabled does not install iBGP learned routes into its routing desk if it isn't always capable of validate those routes in its IGP. Issue the no synchronization command beneath router bgp a good way to disable synchronization. This prevents BGP from validating iBGP routes in IGP.

Q18. How do I configure BGP with the use of a loopback address?

Ans: The use of a loopback interface guarantees that the neighbor remains up and is not suffering from malfunctioning hardware.

BGP makes use of the IP cope with configured at the physical interface immediately related to the BGP peer because the supply cope with whilst it establishes the BGP peering session, by way of default. Issue the neighbor <ip address> replace-supply <interface> command so as to exchange this conduct and configure the BGP that speaks to the router to set up peering with the use of a loopback deal with as the source address.

Q19. Define numerous kinds of communities and why they're used?

Ans: Additionally, there are four properly-knowncommunities that may be referenced by call:

No-export– prevents the path from being advertised outsidethe local AS to eBGP peers.

No-advertise– prevents the path from being advertised to both inner or external peers.

Internet – allows the course to be advertised out of doors the local AS.

Local-AS – prevents the course from being advertised outdoor the nearby AS to either eBGP orconfederate peers.

Q20. What is the default BGP ConnectRetry timer, and is it feasible to track the BGP ConnectRetry timer?

Ans: The default BGP ConnectRetry timer is 120 seconds. Only after this time passes does the BGP procedure take a look at to see if the passive TCP consultation is hooked up. If the passive TCP consultation isn't established, then the BGP system starts a brand new active TCP attempt to connect with the remote BGP speaker. During this idle 120 seconds of the ConnectRetry timer, the far off BGP peer can establish a BGP consultation to it. Presently, the Cisco IOS ConnectRetry timer can not be modified from its default of 120 seconds.

Q21. What additional command do you have to use to set up intraconfederation EBGP periods between loopback interfaces?

Ans: To set up intraconfederation EBGP sessions between loopback interfaces, you need to specify ebgp-multihop on the intraconfederation EBGP neighbor.

Q22. What is the motive of path dampening ?

Ans: Route dampening minimizes the effect of direction flaps in downstream self reliant structures upon neighborhood and upstream autonomous systems.

Q23. In standard which routes will have an effect on by means of direction dampening?

Ans: Route dampening affects simplest EBGP routes.

Q24. How a good deal reminiscence should I have in my router to get hold of the complete BGP routing table from my ISP?

Ans: The quantity of reminiscence required to shop BGP routes relies upon on many factors, consisting of the router, the wide variety of change paths available, route dampening, network, the quantity of maximum paths configured, BGP attributes, and VPN configurations. Without information of those parameters it's far tough to calculate the amount of memory required to shop a positive wide variety of BGP routes. Cisco generally recommends a minimum of 512 MB of RAM in the router to shop a entire worldwide BGP routing desk from one BGP peer. However, it's miles important to understand approaches to lessen memory intake and achieve best routing without the need to get hold of the entire Internet routing desk

Q25. Do internal BGP (iBGP) sessions regulate the subsequent hop?

Ans: iBGP sessions hold the following hop characteristic discovered from eBGP peers. This is why it's miles critical to have an internal course to the next hop. The BGP path is in any other case unreachable. In order to ensure you can attain the eBGP subsequent hop, consist of the community that the following hop belongs to in the IGP or issue the next-hop-self neighbor command to force the router to advertise itself, rather than the external peer, as the next hop.