Network
Layer
Network layer is responsible for
providing logical address know as IP address. Router works on this layer. Main
functions of this layer are following:-
o Define IP address
o Find routes based on IP address
to reach its destination
o Connect different data link type
together like as Token Ring, Serial, FDDI, Ethernet etc.
IP packet
Network layer receive segment
from transport layer and wrap it with IP header that is known as packet.
Datagram
Datagram is just another name of
packet. Network layer use datagram to transfer information between machines.
Two types of packets are used at
the Network layer: data and route updates.
Data packets
Data packets are used to
transport the user data across the network. Protocols used by data packets are
known as routed protocol. For example IP and IPv6
Route update packets
These packets are used to update
routers information within internetwork. Protocols that send route update
packets are called routing protocols; for example RIP, RIPv2, EIGRP, and OSPF.
IP addresses are broken into two components:
o Network component: - Defines network
segment of device.
o Host component :- Defines the
specific device on a particular network segment
IP Classes
Class A addresses range from
1-126.
Class B addresses range from
128-191.
Class C addresses range from
192-223.
Class D addresses range from 224-239.
Class E addresses range from
240-254.
o 0 [Zero] is reserved and
represents all IP addresses;
o 127 is a reserved address and is
used for testing, like a loop back on an interface:
o 255 is a reserved address and is
used for broadcasting purposes.
Class A, B, C address are known
as public address that can be used to access devices in other public networks,
such as the Internet.
Private IP and ISP
Private IP address can be used to
configure private network. You can use private IP to build your network without
paying a single penny. But one biggest problem with private IP is that with
private IP you cannot access the internet. This is the point where ISP comes
from. ISP purchase a bulk of public IP address and provide them on rent.
Whatever you pay to ISP for accessing internet is actually the charge of using
public IP address.
Private IP address: - Not
routable in public network
Class A: 10.0.0.0 -
10.255.255.255
Class B: 172.16.0.0 -
172.31.255.255
Class C: 192.168.0.0 -
192.168.255.255
Network layer protocols that you
should know for exam
Protocol Description
IP IP of TCP/IP, featuring routable 32-bit addressing.
IPX The equivalent of IP in Novell Netware.
ICMP Internet Connection Management Protocol. Incorporates Ping and
Traceroute, which are layer 3 link-testing utilities.
OSPF, IGRP, EIGRP, RIP, ISIS. Dynamic
routing protocols that learn about remote networks and update them other
neighbour routers running the same protocol.
ARP, RARP Address Resolution Protocol (and Reverse ARP). ARP learns what MAC
address is associated with a given IP address. Reverse ARP learns an IP address
given a MAC address.
