Top 25+ Most Asked BGP Interview Questions and Answers
Following is a list of BGP interview questions and answers.
1) What is BGP? What is the full form of BGP?
BGP stands for Border Gateway Protocol. It is a standardized exterior gateway protocol designed to exchange routing and provide information among autonomous systems (AS) on the Internet. BGP is mainly used for routing within an autonomous system. In this application, it is called Interior Border Gateway Protocol, Internal BGP, or iBGP. As the other use, the internet application of this protocol is called Exterior Border Gateway Protocol, External BGP, or eBGP.
We can classify the Border Gateway Protocol as a path vector protocol. It makes routing decisions according to paths, network policies, or rule sets configured by a network administrator. It is also involved in making core routing decisions. For example, when two ISPs connect, they typically use BGP to exchange routing information.
2) Can Routers on different subnets become BGP neighbours?
BGP is usually configured between two directly connected routers that belong to different autonomous systems. BGP routers do not need neighbours to be attached to the same subnet. Instead, they use a TCP connection between the routers to pass BGP messages and allowing neighbouring routers to be on the same or different subnet.
3) What is the main purpose of BGP?
The main purpose of BGP is to exchange routing updates like other routing protocols, but generally, it does not exchange individual network routes. It exchanges summaries of network routes. That's why it is typically used over very large networks, including the Internet.
4) What are some basic characteristics of BGP?
BGP is a path-vector protocol or an exterior gateway protocol (EGP) used in routing on the Internet. Following are the most common characteristics of BGP:
5) What TCP port number does BGP use for connection?
BGP uses TCP port 179 for the connection.
6) What is the main difference between eBGP and iBGP neighbours?
The eBGP is used for external neighbours between different autonomous systems. On the other hand, iBGP is used for internal neighbours within the same autonomous system.
7) Is it possible to run two BGP processes on a single router?
No, it is not possible to run two BGP processes on a single router.
8) Can we use BGP instead of any IGP?
No, we cannot use BGP instead of any IGP because BGP works between different autonomous systems, but IGP works inside an autonomous system.
9) How can we check the BGP status?
There are two ways to check BGP status:
10) What do you understand by peers in BGP?
In BGP, any two routers that formed a TCP connection to exchange BGP routing information are called peers. Peers are also called BGP neighbours.
11) What do you understand by poison reverse in BGP?
In a computer network that uses the Routing Information Protocol (RIP) or other distance vector routing protocols, poison reverse is how a gateway node tells its neighbour gateways that one gateway is unreachable over the interface or no longer connected.
12) What are some BGP timers?
There are mainly two BGP timers:
13) What do you understand by loop prevention mechanism in BGP?
There are two types of loop prevention mechanisms in BGP:
Note: A BGP router does not add its ASN when advertising to an iBGP peer.
14) What is the difference between Hard Reset and Soft Reset in BGP?
In BGP terminology, the administrators are required to reset BGP peers. There are two ways to reset a peer:
Let's see the differences between Hard Reset and Soft Reset in a tabular form:
15) What are BGP Message types? What are the different BGP Message types?
BGP Message types are used to establish a neighbour relationship and exchange parameters, including autonomous system number and authentication values. Following is a list of some BGP Message types:
16) What are some well known BGP metric's attributes?
BGP path selection depends on the values of the attributes. Following is a list of some well known BGP metric's attributes:
17) What do you understand by RIP in networking?
RIP stands for Routing Information Protocol. It is one of the oldest distance-vector routing protocols used to employ the hop count as a routing metric. RIP also prevents the routing loops by limiting the number of hops allowed in a path from source to destination.
18) What is the purpose of BGP MED?
The main purpose of BGPMED is to influence how other autonomous systems enter into your autonomous system to reach a certain prefix. BGP MED is an attribute that is not propagated throughout the whole network but just to adjacent AS. The lower the MED, the more the path will be preferred.
19) What are the different BGP Path Attributes?
BGP supports several Path Attributes varieties and uses these path Attributes to check the competing BGP paths (routes) in the BGP table to find out the best possible path (route).
Following is a list of some BGP Path Attributes:
20) What is the order of preference in BGP?
In BGP, the order of preference varies on whether the attributes are applied for inbound updates or outbound updates.
For inbound updates, the order of preference is:
For outbound updates, the order of preference is:
21) What are the various types of communities used in BGP? Why are they used?
There are four well-known communities used in BGP. The following list specifies their usage:
22) Does BGP support authentication?
Yes. BGP supports MD5 authentication.
23) Does BGP require full mesh?
There are two types of BGP:
24) What do you understand by a route reflector? Why is it required?
A route reflector is a BGP router that can break the iBGP loop avoidance rule. A route reflector can advertise updates received from an iBGP peer to another iBGP peer under specific conditions. Route reflectors are used to eliminate the full mesh requirement by breaking the rule and building iBGP networks that scale easily and cleanly.
25) What is the Admin Distance (AD) of eBGP & iBGP?
Admin Distance of eBGP is 20, and Admin Distance of iBGP is 200.