Basic Questions on BGP

What is the Border Gateway Protocol(BGP)?

Ans: BGP is an exterior gateway routing protocol used to communicate between more than one AS.

Which port is used by BGP?

Ans: BGP uses TCP port number 179.

What is the internal BGP?

Ans: BGP protocol within an autonomous system(AS) is called internal BGP.

What is the external BGP?

Ans: BGP protocol between two autonomous systems (AS) is called external BGP.

Is it possible to run multiple BGP instances at one Router?

Ans: No, One can’t run multiple BGP instances at a single router.

What is the Hello and Dead interval of BGP?

Ans: Hello time: 60 seconds and Dead interval: 180 seconds.

What are Peers in BGP routing protocol?

Ans: Neighbors in BGP are called peers.

What is the metric of a BGP routing protocol?

Ans: BGP uses something called Attributes to determine the best path.

Should neighbor be directly connected in BGP?

Ans: No, it’s not compulsory to be connected directly.

What is the AD value of the BGP routing protocol?

Ans: Internal BGP (iBGP) = 200 and External BGP(eBGP) = 20.

How a BGP is decided as internal BGP and external BGP?

Ans: BGP exchange Open Packet during neighbor formation. In the open packet, BGP router sends information about the autonomous number. If BGP router finds Its own AS number in Open Packet then it is internal BGP otherwise it is external BGP.

How neighbors are configured in BGP?

Ans: Neighbors are configured manually in BGP by using neighbor command.

How loop is prevented in BGP?

If a BGP router finds it’s own AS number in a learned route then the router understands that there is a loop and reject the advertisement/update. Hence loop is prevented in BGP. A BGP router will discard any update/advertisement from any router having its own AS number.

What is the default TTL value in BGP?

Ans: Default TTL in BGP is 1.

What is the synchronization rule in BGP?

Ans: Do not advertise the route through BGP until the same route is learned from IGP.

What are the BGP message types?

Ans: There are four message types in BGP.

  • Open
  • Keepalive
  • Update
  • Notification

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