February 18, 2003 Week 6: Day 2
Welcome to Lesson 6 - Network Communications and Protocols (Cont.)
TCP/IP is the most commonly
used protocol suite because of its cross-platform compatibility and its use
in today’s Internet.
It is important to realize that the TCP model and the OSI model are similar.
Note the following diagram:
More than any other protocol suite, the TCP/IP suite is made up of small, specialized
protocols. For example, in the NWLink suite (discussed later in the chapter),
many functions are handled by IPX. However, in the TCP/IP suite, the FTP protocol
is responsible for file manipulation, the SMTP protocol is responsible for e-mail
transfer, the RIP protocol is used to distribute routing information, etc.
Note: This section is
the most important in this chapter and, perhaps, in the entire course. Current
network topologies and the Internet rely heavily on TCP/IP and fully understanding
IP addressing is imperative.
IP addresses are logical addresses that are 32 bits (4 bytes) long and are represented by decimal numbers from 0 to 255, separated by periods. Each number represents one byte, or octet. An example is 192.156.118.1.
Although eight bits have 256 possible combinations, the decimal numbers 0 and 255 are reserved for special addresses, broadcasts, and special packets. 0 represents the local network address and 255 is used for broadcasts. Real addresses can only use number 1 through 254.
There are two sections of an IP address, the host ID and the network ID. In
the example in the text, 172.24.206.18, the network ID might be 172.24, while
the host ID could be 206.18. The full network address is represented as 172.24.0.0.
All computers on the same network must have the same network ID.
The class system defines which bits of the address denote the host and which
bits denote the network the host is on. This information is used to determine
whether the destination of a packet is on the local network or a remote network.
Note that although the class system is not universally used today, it represents
an easy way to describe a network’s TCP/IP implementation. Any address
beginning with 127, such as 127.115.1.10, is considered the loopback address.
A packet sent to this address is immediately returned without reaching the network
medium. Along the same lines, the host name localhost is reserved and always
represents the local device’s IP address. This is very useful when troubleshooting
TCP/IP problems. If the user PINGs the loopback address or localhost and receives
no response, TCP/IP is not properly loaded or the NIC has failed.
Private addresses are
available for computer networks not connecting to the Internet. If packets with
these addresses are placed on the Internet, they are immediately dropped. The
Internet Engineering Task Force (IETF) is in the process of implementing a new
version of TCP/IP, IPv6. IPv6 addresses are 8 bytes long and could provide a
total of 16 quadrillion IP addresses. CIDR (pronounced cider is a method for
defining which portion of the address is the host and which is the network is
very detailed. It is important o recognize its notation (192.203.187.32 /22
where 22 is the number of bits representing the network ID) and understand how
to calculate the exact network and host IDs represented.
The subnet mask is used
to determine which part of the address is the host and which part is the network.
Discuss the default subnet masks used in the class system: the Class A mask
is 25.0.0.0, the Class B mask is 255.255.0.0, the Class C mask is 255.255.255.0.
The following examples will further help illustrate how subnet masks function.
Ones in the binary section denote network ID, while zeros denote host ID.
IP address: 202.100.99.230
Subnet Mask: 255.255.255.0 (Class C)
Binary Address: 11001010 01100100 01100011 11100110
Binary Mask: 11111111 11111111 11111111 00000000
Binary Network ID: 11001010 01100100 01100011
Binary Host ID: 11100110
Decimal Network ID: 202.100.99
Decimal Host ID: 230
IP address: 152.98.212.156
Subnet Mask: /26 (CIDR)
Binary Address: 10011000 01100010 11010100 10011100
Binary Mask: 11111111 11111111 11111111 11000000
Binary Network ID: 10011000 01100010 11010100 10
Binary Host ID: 011100
Decimal Network ID: 152.98.212.128
Decimal Host ID: 28
LINK to a GREAT Subnet Calculator
You should download and install the following subnet calculator (its free!):
1. To which IP address class does
an address starting with 163 belong? 244? 6?
Think about it, then click HERE
to see the answer.
2. What is the binary value of 26? What is the decimal value of 1011100?
Think about it, then click HERE
to see the answer.
3.Which member of the TCP/IP protocol suite is responsible for associating IP
addresses with MAC
Think about it, then click HERE
to see the answer.
Your network includes three subnets connected through a router. It is necessary for you to use TCP/IP for connectivity to a UNIX system, but it has not yet been installed on the computers. Your network will not be connecting to the Internet. Describe an IP addressing system which will provide your computers the connectivity they need.
Nathan Panzella is responsible for this question.
Quick Question:
Be the first to answer this on the BB: What is the Class of the network at ASU? How do you know this to be true?
Remember to keep up with your on-line lessons and quizzes!
mdm