The document discusses IP addressing and subnetting. It explains that IP addresses are divided into a netid and hostid portion, with the lengths depending on the address class. Subnetting further divides the network portion from the host portion using CIDR notation such as 192.60.128.0/22. This separates the network prefix from the host identifier using a bitwise AND with the subnet mask. The document also mentions network address translation (NAT).

1. UNIT IV

12. In classful addressing, an IP address of class A,B and C is divided into
two parts : netid and hostid.
The netid and hostid are of varying lengths, depending on the class of the
address.
Netid: The part of an IP address that identifies the network.
Hostid: The part of an IP address that identifies a host in a network.
The mask can help us to find the netid and hostid.
The last column shows the mask in the form /n where n can be 8, 16 or 24 in
classful addressing . This notation is also called slash notation or Classless
Inter Domain Routing (CIDR).

14. What is Subnetting?
Process of dividing an IP network in to sub divisions is called subnetting.
Subnetting divides an IP address in to two parts as the network (or routing
prefix) and the rest field (which is used to identify a specific host).
CIDR notation is used to write a routing prefix.
This notation uses a slash (/) to separate the network starting address and the
length of the network prefix (in bits).
For example, in IPv4, 192.60.128.0/22 indicates that 22 bits are allocated for
the network prefix and the remaining 10 bits are reserved for the host address.
In addition, routing prefix can also be represented using the subnet mask.
255.255.252.0 (11111111.11111111.11111100.00000000) is the subnet mask
for 192.60.128.0/22. Separating the network portion and the subnet portion of
an IP address is done by performing a bitwise AND operation between the IP
address and the subnet mask. This would result in identifying the network prefix
and the host identifier.

39. NAT: Network Address Translation