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Topic 6: Network Layer - Chapter 5 : The Internet: Addressing & Services Business Data Communications, 4e Internet Addressing 32-bit global internet address Includes network and host identifiers Dotted decimal notation 11000000 11100100 00010001 00111001 (binary) 18.104.22.168 (decimal)
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Business Data Communications, 4e
Address Example Software Example Address
Application Layer Web browser ike.ba.ttu.edu
Network Layer TCP/IP 22.214.171.124
Data Link Layer Ethernet 00-A0-C9-96-1D-90
The network layer determines the best route through the network to the final destination.
Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent.
In general, the data link layer address is permanently encoded in each network card, and as part of the hardware that cannot be changed.
Network layer addresses are generally assigned by software. Every network layer software package usually has a configuration file that specifies the network layer address for that computer.
Application layer addresses (or server addresses) are also assigned by a software configuration file. Virtually all servers have an application layer address, but most client computers do not.
Network layer addresses and application layer addresses go hand in hand. (ruby.bus.utexas.edu - means 126.96.36.199 at the network layer.)
InterNIC is responsible for network layer addresses (IP addresses) and application layer addresses or domain names (www.ttu.edu).
There are five classes of Internet addresses.
Classes A, B, and C are available to organizations
Class D and E are reserved for special purposes and are not assigned to organizations.
Ranges of the first byte for different classes:
Class D Class E
Class A: 0xxxxxxx
Class B: 10xxxxxx.xxxxxxxx
Class C: 110xxxxx.xxxxxxxx.xxxxxxxx
Class D: 1110xxxx.xxxxxxxx.xxxxxxxx
Class E: 1111xxxx.xxxxxxxx.xxxxxxxx
The IP addresses with the first
byte as 0 and 127 are reserved
# of Addresses
Class Available Addr-Structure Example Available#
Class A 16 million First byte fixed 50.x.x.x 126
last three bytes
Class B 65k First two bytes fixed 128.192.x.x 16k
last two bytes
Class C 254 First three bytes fixed 192.1.56.x 2 millions
The Internet is quickly running out of addresses. Although there are more than 1 billion possible addresses, the fact that they are assigned in sets (or groups) significantly restricts the number of usable addresses.
The IP address shortage was one of the reasons behind the IPv6, providing in theory, 3.2 x 1038 possible addresses.
How to apply for IP address?
Assign IP addresses to specific computers so that all computers on the same local area network have a similar address.
Each LAN that is logically grouped together by IP number is called a TCP/IP subnet.
Subnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing.
IP address: 188.8.131.52
Subnet mask: 255.255.255.0
IP address: 129.118.49.x is for the computers in the same subnet
Subnet with partial bytes addresses.
E.g. 184.108.40.206 to 220.127.116.11
Subnet mask: 255.255.255.128
Subnet address: 18.104.22.168
Subnet broadcast address: 22.214.171.124
126.96.36.199 1000 0001.0111 0110.0011 0001.0110 1111
255.255.192.0 1111 1111.1111 1111.1100 0000.0000 0000
The IP prefix 1000 0001.0111 0110.00
188.8.131.52 1000 0001.0111 0110.0011 0011.0110 1111
184.108.40.206 1000 0000.0101 0011.0111 1111.0000 0001
Subnet Mask Template
128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
1 0 0 1 0 1 1 0
0 0 0 0 0 0 0 1
Network ID–Class B
Possible Subnet Address
An address assignment problem:
Each time the computer is moved, or its network is assigned a new address, the software on each individual computer must be updated.
Solution: dynamic addressing
With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network.
Two standards for dynamic addressing are commonly used in TCP/IP networks:
The Bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses.
Dynamic addressing greatly simplifies network management in non-dial-up networks too.
The sender translates the application layer address (or server name) of the destination into a network layer address; and in turn translates that into a data link layer address.
Two approaches used in TCP/IP:
Domain Name Service (DNS)
Used for translating application layer addresses into network layer addresses.
Keeps the name and IP addresses of the name server that will provide DNS information for your address classes.
Server address resolution process:
This is why it sometimes takes a long time to access certain sites.
IP addresses are then temporarily stored in a server address table.
In order to actually send a message, the network layer software must know the data link layer of the destination computer.
In the case of a distant computer, the network layer would route the message by selecting a path through the network that would ultimately lead to the destination.
There are many possible routes or paths a message can take to get from one computer to another.
The process of determining the route or path through the network that a message will travel from the sender to the receiver.
The routing information on each router, which specifies how message will travel through the network.
There are three commonly used dynamic routing protocols
Two ways a group of packets can be routed:
TCP vs. UPD
The usual transmission between two computers.
Sending messages to all computers on a LAN or subnet.
Sending the same message to a group of computers temporarily in a class D IP address. IGMP is used for multicast.
An IPv6 transmission method allowing messages to be sent to any one of the host in a sub-network.
Quality of Service (QoS):
RT + B
R: Token replenishment rate
B: Bucket size
At least four pieces of information needed for a client computer TCP/IP configuration
What is a port address?
Why need port addresses?
IP version 6 (IPv6) will be unrolled in three waves extending from mid-2001 through 2003:
ISPs and manufacturers of equipment such as routers and switches expect to benefit by accelerating their own IPv6 development initiatives. The first wave is expected to hit at the same time Microsoft introduces Windows XP in October of this year, thus changing over its PC line to IPv6. The first manifestations of the second wave will be home gateways and IPv6-enabled game consoles, followed by AV gear such as DVD players and camera-equipped VCRs. NTT DoCoMo and the J-Phone Group are among the cellular carriers readying IPv6-capable products in preparation for the third wave in early 2003.