What are the interview questions for BGP?

BGP Interview Questions for Experienced

  • Differentiate between Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP).
  • Differentiate between hard reset and soft reset in the context of BGP.
  • What do the various BGP Path Attributes mean?
  • What do you understand about communities in the context of BGP?

Can you explain BGP in detail?

Border Gateway Protocol (BGP) refers to a gateway protocol that enables the internet to exchange routing information between autonomous systems (AS). As networks interact with each other, they need a way to communicate. This is accomplished through peering. BGP makes peering possible.

How do you stop a loop in BGP?

In BGP there are two loop prevention mechanism:

  1. For EBGP there is AS-Path attribute which states that router will drop BGP advertisement when it sees it own AS number in AS path attribute.
  2. For IBGP there is split horizon rule which states that update sent by one IBGP neighbor should be not send to another IBGP neighbor.

What is split horizon in BGP?

The BGP split-horizon rule states that a BGP router that receives a BGP route via an iBGP peering shall not advertise that route to another router that is an iBGP peer. It is important that you commit this rule to memory. By doing so, you will be able to recognize when this is the reason for missing routes.

How does BGP select path?

BGP Table path selection

  • Prefer the highest local-preference value.
  • Prefer the shortest AS-path length.
  • Prefer the lowest origin value.
  • Prefer the lowest MED value.
  • Prefer routes learned from an EBGP peer over an IBGP peer.
  • Prefer best exit from AS.
  • For EBGP-received routes, prefer the current active route.

Is BGP link state or distance vector?

“Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information between autonomous systems (AS) on the Internet. The protocol is often classified as a path vector protocol but is sometimes also classed as a distance-vector routing protocol.”

What metric does BGP use?

The BGP MED attribute, commonly referred to as the BGP metric, provides a means to convey to a neighboring Autonomous System (AS) a preferred entry point into the local AS. BGP MED is a non-transitive optional attribute and thus the receiving AS cannot propagate it across its AS borders.

Does BGP use TCP or UDP?

TCP port
BGP uses TCP port 179 to communicate with other routers. TCP allows for handling of fragmentation, sequencing, and reliability (acknowledgement and retransmission) of communication packets.

Why does BGP use loopback?

The use of a loopback interface ensures that the neighbor stays up and is not affected by malfunctioning hardware, the main benefit from using loopbacks is that it will not bring down the BGP session when there are multiple paths between the BGP peers, which would otherwise result in tearing down the BGP session if the …

How does BGP calculate best path?

If there are no specific settings that can affect the outcome, BGP Best Path Selection Algorithm determines the best route by selecting the shortest path to the destination. An Autonomous System is a single network or a set of networks and routers, which are under the control of one administrative entity.

What OSI layer is BGP?

Layer 4
BGP in networking is based on TCP/IP. It operates on the OSI Transport Layer (Layer 4) to control the Network Layer (Layer 3).

Does BGP use multicast?

MP-BGP supports unicast and multicast, and constructs different network topologies for each. MP-BGP can maintain unicast and multicast routes based on routing policies. The unicast routing policies and configurations supported by BGP-4 can mostly be applied to multicast.

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