BGP Interview Questions & Answers

 

BGP is which type of Routing Protocol?

BGP is a Path Vector Routing Protocol. It falls under the category of EGP (Exterior Gateway Protocol)

 

Which algorithm is used by BGP for best path selection?

BGP uses Composite Metric for best path selection and install the best routes into the routing table

 

What are BGP Path attributes?

BGP uses multiple attributes or metrics for best path selection which are Weight (cisco), LOCAL_PREF, aggregate, as_path, origin, MED, neighbor type (ebgp > ibgp), igp metric (next_hop), route age, router ID (originator ID), Neighbor IP



How many neighbor states are there in BGP ?

BGP has 6 neighbor states:

Idle, Connect, Active, OpenSent, OpenConfirm, Established

 

Which port is used by BGP for its communication?

BGP uses TCP Port 179

 

What is official standard of BGP?

Official standard RFC for BGP is IETF RFC4271 (BGPv4 – 2006)

 

Does BGP support authentication?

Yes, BGP supports MD5 authentication

 

How many packet types are there in BGP?

There are four types of packet in BGP:

Open, Update, Keepalive, Notification




What is the purpose of each type of BGP packet?

1.    Open Message: Set up and establish BGP adjacency

2.    Update Message: Advertise, update & withdraw routes

3.    Keepalive Message: Ensure that BGP neighbors are still alive

4.    Notification Message: Error Condition notification

 

What is BGP Origin Code?

The BGP Origin Code is one of the attribute that is used for path selection. There are three BGP origin codes called as IGP, EGP & Incomplete as in below:



How many types of BGP are there in total?

There are two types of BGP:

1.    eBGP (External Border Gateway Protocol)

2.    iBGP (Internal Border Gateway Protocol)

 

What are the differences between iBGP & eBGP?

There are many differences between iBGP & eBGP as in below table:



Does BGP require full mesh?

iBGP requires a Full Mesh topology,

eBGP does not require a Full Mesh topology.

 

What is the Admin Distance (AD) of eBGP & iBGP?

Admin Distance of eBGP is 20

Admin Distance of iBGP is 200

 

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