Network Layer
Network layer is responsible for sending and receiving information through network. It uses IP to send and receive data. Like ethernet frame in Data-link layer, Network layer uses IP datagram to send and receive data. It has several fields like Header, flag, Identification, source and destination address and such fields. If a client has to send a data which is larger then the size of the IP datagram. then the data is fragmented and sent to other user. To identify the order of the data, Identification field is used. Flag indicates whether the data has been fragmented or not.
These fragmented IP datagrams are received on the other used side and encapsulated to represent the original data.
IP Address
IP address is used to specify a network. IP address is automatically assigned by protocol named DHCP (Dynamic Host Configuration Protocol). IP address has two types Static IP and Dynamic IP. Static IP is used by the network organizations while the Dynamic IP is used all users which is assigned by the DHCP.
IP address is a 32 bit number which is separated by a decimal value at each octet. It has two parts Network Id and a Host Id.
IP Address Class
If first octet is used as network id and remaining as host, then its Class A. If first two octet is used as network id and remaining as host id, then its Class B. If first three octet is used as network id and remaining as host id, then its Class C.
ARP (Address Resolution Protocol)
ARP is used to identify the hardware address of a node with the help of IP address. ARP maintains a ARP table where it contains MAC address for the corresponding IP address. If Mac address not found, the ARP will send a broadcast message to every nodes. The node which is intended to receive the message will send a ARP response with a Mac address to the node with sent a broadcast.
Subnetting
Subnetting is process of splitting the network into smaller one. Subnet mask is helps to identify the network id and host id. Subnet mask is a 32 bit number, where the network bits are assigned to 1 and the host bits are assigned to 0. With AND or OR operation in IP and Subnet mast, the network id or host id can be easily extracted for the IP.
CIDR (Classless inter Domain Routing)
Each octet ranges between 0-255 (2^8). 0 cannot be used and 255 is reserved as for the broadcast. if a organization needs a IP with just more than 300, then they have to choose Class B instead of Class C. This will result is wastage of 60000+ space. To overcome this, CIDR was introduced where the is host id is assigned based on requirement. It is assigned as 9.100.100.100 / 23. The 23 denotes that the first 23 bits of 32 will be used as the network id and the other 9 bits will be used as the host id.
Router
Router is network device which is used to send and receive data packets through networks. It has four main steps 1) Receives the data packet. 2) Examines the IP datagram 3) Looks for the destination network. 4) Send packet to the destination network or to the router which is nearer to destination network.
Router maintains a routing table which has fields like next hop, total hop, destination network. Hop is a rough measure of distance between the two routers.
Routing Protocols
Routing protocols are divided into two Interior gateway protocols and Exterior gateway protocols.
Interior gateway protocol are used within a Autonomous System and are further divided into 2 Link State Routing Protocol and Distance Vector Protocol. In Distance vector protocol router will be connected to the nearest one and thus it takes some time when network changes. In Link State Protocol, every router will be connected to every other router so transmission will take soon.
Exterior gateway protocol are used to connect with the various Autonomous systems. Most commonly used exterior protocol is BGP (Border gateway protocol)
Non-Routable Address Space
In this method, the gateway protocol will not transfer the traffic to the Non-Routable Address but the nodes can communicate within the autonomous system.
Demarcation Point is a point where one network end and other network starts.
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