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One of the most complex tasks
TCP/IP has to perform is to
determine whether or not a given
IP address exists on the same
subnet. The task isn’t really
that complicated once you
understand how TCP/IP uses its
IP address and subnet mask. An
IP address looks something like
this: 192.168.10.52. IP
addresses always contain four
numbers from 0–255, separated by
periods.
A
portion of the IP address is
called the network ID and acts
as a unique identifier for a
particular subnet. The rest of
the IP address is called the
host ID and identifies a
particular computer or network
device on that subnet uniquely.
How can you tell which part of
the IP address is which? By
using the subnet mask. A subnet
mask looks a lot like an IP
address, with four groups of
numbers: 255.255.255.0.
Remember, computers are binary
machines that can understand
only in zeros and ones.
For the subnet mask to make
sense, you have to translate it
and the IP address into binary.
You can switch the Windows
Calculator into Scientific view,
which enables you to convert
numbers from decimal to binary.
Tip Convert all the four groups
(octets) of numbers into binary
code. For example, an IP address
of 192.168.10.41 and a subnet
mask of 255.255.255.0 look like
this in binary:
Address or Mask 1st octet 2nd
octet 3rd octet 4th octet
192.168.10.41 11000000 10101000
00001010 00101001 255.255.255.0
11111111 11111111 11111111
00000000
Everyplace you see a “1” in the
subnet mask corresponds to the
portion of the IP address that
is the network ID. Everyplace
you see a “0” in the subnet mask
corresponds to the portion of
the IP address that is the host
ID.
Here, the network ID is
192.168.10, and the host ID is
41.TCP/IP treats everything with
an IP address that starts with
192.168.10 as if it were on the
same subnet. Any IP address that
starts with something other than
192.168.10 is treated as if it
existed on another subnet.
Basic TCP/IP Services A number
of the protocols in the TCP/IP
suite are considered core
protocols, which means they are
usually present on any network
that uses TCP/IP. The core
protocols provide basic services
that no network can do without.
These services include _ Data
transmission. Is handled by more
than one protocol: the User
Datagram Protocol (UDP) and the
Transport Control Protocol
(TCP). Computers use UDP when
they need to send a small packet
of data and don’t care if the
remote computer actually
receives the data.
Computers use TCP when loads of
data needs to be transmitted
because TCP allows the remote
computer to reply, confirming
its receipt of the data. _ Name
resolution. Provided by the
Domain Name System, or DNS,
protocol. DNS enables people to
use easy-to-remember names like
www.microsoft.com and allows
computers to translate those
names to numeric IP addresses. _
Windows Internet Name System
(WINS). Prior versions of
Windows also use WINS to convert
computer names into IP
addresses. Windows Server 2003
is compatible with WINS.
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