Protocols in Network layer

Computer Networks:

Physical Layers

Data link Layer(DLL)

Network Layer

Transport Layer:

Session and Presentation Layer:

Application Layer:

Network Layer Protocol

The diagram show the (Network Layer Protocol ) Protocol present at network layer.

Address resolution protocol (ARP):

The ARP address resolution protocol associate in IP address with the physical address. On a typical physical network, such as LAN, each device on a link is identified by a physical or station address usually printed on the network interface card NIC.

Physical address have local address which can be changed easily. for example if the NIC on a particular machine fails, the physical address changing.

The IP address on the other hand has Universal jurisdiction and cannot be change.ARP is used to find the physical address of the node when it internet address is known.

Every Host on the network received and process the ARP packet but only the intent receipt recognize it internet address and send back it physical address. the address of the target host both to its cache memory and to the datagram header then send that datagram on it way.

Reverse address resolution protocol (RARP):

The reverse address resolution protocol (RARP) allow a host to discovered its internal address when it known only its physical address.

The question is why we need RARP.

A host is supposed to have its internal address Store on its hard disc!.

Answer true but what if the host is DISKLESS computer or what if the computer is being connected to the internet for the first time or what if you get a new computer but decides to keeps the old NIC.

RARP works much like ARP the host wish to retrieve it internal address broadcast an RARP query packet that content its physical address to every host on its physical network. A server on the network recognized the RARP packet and returns the host internal address that is IP address.

Internal Control Message Protocol (ICMP)

The internet control message protocol (ICMP) is a mechanism used by host and routers to send notification of datagram problem back to the SENDER.

As we saw above IP is essentially and unreliable and connectionless protocol. ICMP allow Internet Protocol to inform a sender end. if a datagram is undelivered. A datagram travels from router to router until its reach one that can deliver it to it Final Destination. If a router is unable to write a delivered the datagram because of unusual condition or because of network connection.

ICMP use echo Test/reply to test whether a destination is reachable and responding.

Note

Datagram carries only the address of the original sender and the final destination it does not know the address of the previous router that passed it alone. For this reason ICMP can send message only to the source not to the intermediate router.

Internal Group Message Protocol (IGMP)

The Internet Protocol can be associated with two sorts of communication. Unicasting and multicasting.

The internet group message router identifying the host in a LAN that are member of multi-cast group. It is companion to IP protocol.