Network security

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. Without it, networks would not be able to send and receive information with each other.
When you have a network router that connects to other networks, it does not know which network is the best one to send its data to. BGP takes into consideration all the different peering options a router has and chooses the one closest to where the router is. Each potential peer communicates the routing information it has and that gets stored within a routing information base (RIB). BGP can access this information and use it to choose the best peering option.

Data Link Layer is second layer of OSI Layered Model. This layer is one of the most complicated layers and has complex functionalities and liabilities. Data link layer hides the details of underlying hardware and represents itself to upper layer as the medium to communicate.
Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware. At the receiving end, Data link layer picks up data from hardware which are in the form of electrical signals, assembles them in a recognizable frame format, and hands over to upper layer.

Data link layer has two sub-layers:
1. Logical Link Control: It deals with protocols, flow-control, and error control
2. Media Access Control: It deals with actual control of media

The OSI model was developed by the International Organization for Standardization. There are 7 layers:
Physical (e.g. cable, RJ45)
Data Link (e.g. MAC, switches)
Network (e.g. IP, routers)
Transport (e.g. TCP, UDP, port numbers)
Session (e.g. Syn/Ack)
Presentation (e.g. encryption, ASCII, PNG, MIDI)
Application (e.g. SNMP, HTTP, FTP)

Open shortest path first (OSPF) is a link-state routing protocol that is used to find the best path between the source and the destination router using its own shortest path first (SPF) algorithm. A link-state routing protocol is a protocol that uses the concept of triggered updates, i.e., if there is a change observed in the learned routing table then the updates are triggered only, not like the distance-vector routing protocol where the routing table is exchanged at a period of time.

Criteria – 
To form neighbourship in OSPF, there is a criterion for both the routers: 
It should be present in the same area.
The router I’d be unique.
The subnet mask should be the same. 
Hello, and the dead timer should be the same. 
The stub flag must match. 
Authentication must match.

A router is a device that connects two or more packet-switched networks or subnetworks. It serves two primary functions: managing traffic between these networks by forwarding data packets to their intended IP addresses, and allowing multiple devices to use the same Internet connection.

Switches facilitate the sharing of resources by connecting together all the devices, including computers, printers, and servers, in a small business network. Thanks to the switch, these connected devices can share information and talk to each other, regardless of where they are in a building or on a campus.