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Network Layer

  • use
    • manages device addressing
    • tracks the location of devices on the network.
    • determines the best path to move data from source to the destination
    • routers used in this layer
    • ip address
    • source and destination address headers are added
    • routing is done
  • protocols
    • IP
    • IPv6
    • SCP
    • ARP
    • RARP
    • ICMP
    • IGMP
  • pdu
    • packets

IP Addressing

  • IP Address - consists of two parts
    • network id - identify the network
    • host id - get the host

  • Where is port number then?

    • if you visit a web page in the browser then
    • you are using http which has a predefined port no - 80

  • the service that is used to convert the domain name to is called Domain name Service.

  • port number is used to identify a particular process in the host For well known services the port number is already predefined and fixed
    • http - 80
    • https
    • smtp - 25
    • ftp - 21
  • even though your intention is to reach google.com you are visiting DNS firsts and then getting IP address of google.com and then visiting the google home page.

  • This is actually overhead which is also called DNS overhead.

  • \(2^32\) ip address possible if we use 32-bit number

IP address types

  • class A - starts with 0
  • class B - starts with 10
  • class C - starts with 110
  • class D - starts with 1110

  • class E - starts with 1111

  • class A - \(2^7\) networks and \(2^{24}\) hosts

  • class B - \(2^{14}\) networks and \(2^{16}\) hosts
  • class C - \(2^{21}\) networks and \(2^8\) hosts
  • class D - used for multicasting
  • class E - used for military application
class ip subnet use
A 1-127.x.x.x 255.0.0.0 huge corporations
B 128-191.x.x.x 255.255.0.0 big companies
C 192-223.x.x.x 255.255.255.0 small companies
D 224-239.x.x.x multicast
E 240-255.x.x.x research/development

but some are reserved for private use in each class

  • class A - 10.0.0.0 - 10.255.255.255
  • class B - 172.16.0.0 - 172.16.0.0
  • class C - 192.168.0.0 - 192.168.255.255

Note

  • 127 - 0111 1111 - + 64 + 32 + 16 + 15
  • 191 - 1011 1111 - 128 + + 32 + 16 + 15
  • 223 - 1101 1111 - 128 + 64 + + 16 + 15
  • 239 - 1110 1111 - 128 + 64 + 32 + + 15
  • 255 - 1111 1111 - 128 + 64 + 32 + 16 + 15

how to remember

  • 127 + 64 - 191
  • 191 + 32 - 223
  • 223 + 16 - 255

so we can recognize the class of ip using first four bit

Starting Bit Class
0 A
10 B
110 C
1110 D
1111 E

subnetting

  • dividing network in smaller networks