IP addressing

IP addressing

1. Structure of IP Address

   • Consists of Binary 32 bits
     • 4 Octets of 8 bits per octet = 32 bits!
     • All hosts (interfaces) have an ip address from a local network connection
       • These Logical adresses consist of network ID and unique host ID
         • Network ID/Host ID breakdown
           • Class A: NNN.HHH.HHH.HHH
           • Class B: NNN.NNN.HHH.HHH
           • Class C: NNN.NNN.NNN.HHH
       • Subnet mask determines the division between the network bits and Host bits
         • Class A Subnet Mask : 255.0.0.0
         • Class B Subnet Mask: 255.255.0.0
         • Class C Subnet Mask: 255.255.255.0
         • Class D and Class E do not have a Subnet Mask!
   • Assigned by Internet Service Provide
   • the Address resolution protocol (ARP) assigns IP's to Mac addresses

2. IP Classes

   • Class A 1-126
     • Net.Hst.Hst.Hst
     • Octet contains 1-126
     • Octet starts with 0xx.xxx.xxx.xxx
       • Cannot be 000.xxx.xxx.xxx (Invalid host)
       • Cannot be 127- that is reserved to Network Interface Controller (NIC)
       • Cannot be 010.xxx.xxx.xxx As that is reserved
     • has 125 address avaliable. 2^24 - 2 (2 for network and host bits)
       • the 24 is derived from how many Host are available. In this case there are 3 octets available since the first one is used
   • Class B 128-192
     • Consists of the following Network/Host: NNN.NNN.HHH.HHH
     • Has 2^16-2 hosts
     • Can't include:
       • Private classes include 172.16.xxx.xxx to 172.31.xxx.xxx
       • APIPA address generated when DHCP is not available is 169.254.xxx.xxx
   • Class C 192-223
     • Has Host subnet of NNN.NNN.NNN.HHH
     • has 2^8-2 hosts
     • Cant include :
       • 192.168.xxx.xxx
   • Class D: Non Routeable
     • Multicast class
   • Class E: Non Routable
     • Experimental class

3. 127.0.0.1 is the loop back address

4. Network bits must be similar for two hosts to connect

5. IP address is assigned two ways:

   • Dynamic:
     • Dynamic Host Configuration protocol (DHCP) server assigns IP address
       • Assigns IP addresses to MAC addresses.
       • Process of offering a IP address
         • Discover
         • Offer
         • Request
         • Acknowledge
     • Automatic and no human error
     • IP addresses can be reused as they can be released back to the server when finished or lease time expires
   • Static:
     • Assigned by network administrator
     • IP addresses never change

6. IP addresses are maped to MAC address with ARP (Address resolution Protocol) || RARP resolves MAC address to IP address

   • MAC address is the Hardware address. This is needed of the host who is sending a packet to the receieving host
     • Block ID: first 6 digits specific to manufacturer
     • Device ID: Last 6 digits. Consists of Model specific address + date the part was made
   • ARP can figure out the MAC address of a host that is on the same local network
     • If IP destination is on a remote/another network then the MAC address (default gateway) is used
   • cannot route ARP!
   • arp -a is the arp command that brings up cached entries
   • ARP table stores the physical port of a host