Most frequently Asked Border Gateway Protocol (BGP) Interview Questions

1. What is BGP?
2. What are the features of BGP?
3. How do we check the BGP status?
4. What are the BGP timers?
5. What are BGP Message Types?
6. Name some BGP metric's attributes?
7. What is Poison Reverse?
8. What are the types of Communities used in BGP?
9. What is BGP Local Preference?
10. What are the types BGP Routing Table?
11. What is BGP TLL Security?
12. What is Split-Horizon?

What is BGP?

Border Gateway Protocol helps in the dynamic routing protocol used on the Internet. It also helps in connecting different ISPs and in operating with a large amount of data, it operates from the internal dynamic routing protocols(IGP).BGP also is considered as a path vector protocol and its routing methods are based on these paths, the network policies sets are by a network administrator.

What are the features of BGP?

Some features of BGP are as follows:

• BGP helps in sending updates when changes occurs in the Network.
• BGP sends messages for verifying TCP Connections.
• BGP is a routing protocol which is best for strategic routing policies.
• BGP outbounds the traffic from single router locally.
• BGP uses confederations for reducing BGP peering overhead.

How do we check the BGP status?

There are 2 ways used for checking the BGP status:
For checking BGP Configuration, we need to enter show config in the Configuration Router BGP Mode.
For checking BGP Status, we need to use the IP BGP summary command in the Exec Privilege Mode.

What are the BGP timers?

There are 2 type of BGP Timers:
Keepalive Interval helps in specifying time in seconds between sending keepalive messages.Its default timer is 30 seconds.
Hold Time helps in specifying the interval time in seconds.Its default timer is 180 seconds.

What are BGP Message Types?

BGP Message Types are used for establishing neighbour relationship and in exchanging parameters that consists Autonomous System Number and Authentication Values.
There are four types of BGP Message Types:


Open - helps in creating neighbor relationships and exhanging parameters.
Keepalive - helps by maintaining neighbor relationship and is the keepalive message is not received the BGP neighborship is turned down.
Update - helps in exchanging path attributes and associates prefix by using those attributes.
Notification - helps in reporting BGP Erors.

Name some BGP metric's attributes?

BGP metric attributes are as follows:
Weight
Local Preference
Originate
AS path length
Origin code
MED
Oldest Path
Router ID
Neighbor IP address

What is Poison Reverse?

Poison Reverse in BGP helps by sending metrics to the routers and informing the other routers about its secondary paths that can have an infinite hop count and will cease forwarding packets to each other.
Poison Reverse is used by a protocol such as:
Routing Information Protocol(RIP)
Internetwork Packet Exchange Routing Information Protocol(IPX RIP)
Interior Gateway Routing Protocol(IGRP)
EIGRP
AppleTalk Routing Table Maintenance Protocol(RTMP)

What are the types of Communities used in BGP?

Types of Communities in BGP are as follows:

• No-export - used for preventing route from being advertising outside the local autonomous systems.
• No-advertise - used for preventing the route from being advertising to internal peers or external peers.
• Internet - used in advertising the route outside the local autonomous system.
• Local-AS - helps by preventing routing from advertising it to the outside autonomous system from the confederate peers.

What is BGP Local Preference?

Local Preference indicates AS about the path that has the preference to exit the AS for reaching a network. It has a higher path and has a default value for local preference is 100 and also can be changed. It is communicated by a single AS for influencing the choice to exit the AS.

What are the types BGP Routing Table?

BGP Routing Table helps in storing the routes and processing them for the best calculation. It contains 3 types of the table for storing incoming routes from the neighbors, for sending the routes to the neighbors and installing routes where we can find the routes with next-hop address.
Types of BGP Routing Table are:
Adj-RIB-in
Adj-RIB-out
Loc-RIB

What is BGP TLL Security?

BGP TTL Security is used in protecting our eBGP session like DOS attacks.It can also check and be used only with eBGP sessions and not iBGP session.

What is Split-Horizon?

Split Horizon is a rule which helps in routing information that cannot be sent back to the xrouter from which it can be received. The routing information is not sent back in the direction from that side it can be received. It is also used in preventing routing loops in the network.