A bit on internet addresses.

IPv4

• 32 bit addresses divided into 8 bit blocks.
• Has private address range and multicast address range.

Classful networking

• 0xxxxxxx.x.x.x is one network. Called class A.
  • Has 128 possible networks. Size of network is 224
  • Has subnet mask equal to 8.
• Similarly 10xxxxxx.x.x.x is another network. Class B.
  • Has 214 networks. Network size decreases inversely.
  • Has subnet mask equal to 16.
    • Similarly class C has subnet of 24.
• Only allowed for 254 networks.

Fun fact: ARPAnet was 10.x.x.x

private address range

Block Size	Range	Bit mask	Classful description
24-bit	10.0.0.0 - 10.255.255.255	8	One class A network
20 bit	172.16.0.0 - 172.31.255.255	12	16 contiguous class B networks
12 bit	192.168.0.0 - 192.168.255.255	16	256 contiguous class C networks

Loopback interface

• Special case of private addresses.
• Packets never leave the host.
• 127.0.0.0/8 is the address space reserved for ipv4.

IP Broadcast

• In IPv4 it has a special address. This was used by interfaces to send messages to all networks connected to a particular subnet.
• In dhcp, if the broadcast address of the subnet is not defined, then a DHCPDISCOVER message is sent to the address 255.255.255.255.
• This again does the same job of keeping the broadcast message within the same subnet.
• The broadcast address is otherwise calculated as follows: - Take the first subnet bits of the network. Let them be as they are. - Change the remaining trailing bits to 1.