Abstract of CCNA study guide-9 - tcp/ip 4

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IP Addressing

IP Terminology

Bit A bit is one digit, either a 1 or a 0.

Byte A byte is 8 bits.

Octet  is 8 bits, byte and octet are the same.

Network address This is the designation used in routing to send packets to a remote network

Examples 10.0.0.0, 172.16.0.0, and 192.168.10.0.

Broadcast address The address used by applications and hosts to send information to all nodes on a network . Examples  255.255.255.255,which is all networks, all nodes; 172.16.255.255, which is all subnets and hosts on network 172.16.0.0; and 10.255.255.255, which broadcasts to all subnets and hosts on network 10.0.0.0.

The Hierarchical IP Addressing Scheme

An IP address consists of 32 bits of information. These bits are divided into four sections, referred to as octets or bytes, each containing 1 byte (8 bits).

You can depict an IP address using one of three methods:

-Dotted-decimal, as in 172.16.30.56

-Binary, as in 10101100.00010000.00011110.00111000

-Hexadecimal, as in AC.10.1E.38

Network Addressing

The network address (which can also be called the network number) uniquely identifies each network. Every machine on the same network shares that network address as part of its IP address. In the IP address 172.16.30.56, for example, 172.16 is the network address.

The node address is assigned to, and uniquely identifies, each machine on a network. This part of the address must be unique because it identifies a particular machine. This number can also be referred to as a host address. In the sample IP address 172.16.30.56, the 30.56 is the node address.

The designers of the Internet decided to create classes of networks based on network size.

For the small number of networks and a very large number of nodes, they created the rank Class A network.

For the numerous networks with a small number of nodes there is  the Class C network

The class distinction for networks between very large and very small is predictably called the Class B network.

Network Address Range: Class A

the first bit of the first byte in a Class A network address must always be off, or 0. This means a Class A address must be between 0 and 127

Network Address Range: Class B

In a Class B network the first bit of the first byte must always be turned on but the second bit must always be turned off. If you turn the other 6 bits all off and then all on, you will find the range for a Class B network between 128 and 191

Network Address Range: Class C

For Class C networks the first 2 bits of the first octet as always turned on, but the third bit can never be on.

the range for a Class C network between 192 and 223

Network Address Ranges: Classes D and E

The addresses between 224 to 255 are reserved for Class D and E networks. Class D (224–239) is used for multicast addresses and Class E (240–255) for scientific purposes.

Network Addresses: Special Purpose

Some IP addresses are reserved for special purposes, so network administrators can’t ever assign these addresses to nodes. Table 2.4 lists the members of this exclusive little club and the reasons why they’re included in it.

Class A Addresses

Class A Valid Host IDs

Here’s an example of how to figure out the valid host IDs in a Class A network address:

- All host bits off is the network address: 10.0.0.0.

- All host bits on is the broadcast address: 10.255.255.255.

The valid hosts are the numbers in between the network address and the broadcast address: 10.0.0.1 through 10.255.255.254

Class B Addresses

Class B Valid Host IDs

Here’s an example of how to find the valid hosts in a Class B network:

_ All host bits turned off is the network address: 172.16.0.0.

_ All host bits turned on is the broadcast address: 172.16.255.255.

The valid hosts would be the numbers in between the network address and the broadcast address: 172.16.0.1 through 172.16.255.254.

Class C Addresses

Class C Valid Host IDs

Here’s an example of how to find a valid host ID in a Class C network:

_ All host bits turned off is the network ID: 192.168.100.0.

_ All host bits turned on is the broadcast address: 192.168.100.255.

 The valid hosts would be the numbers in between the network address and the broadcast address: 192.168.100.1 through 192.168.100.254.

Private IP Addresses

private IP addresses can be used on a private network, but they’re not routable through the Internet.

This is designed for the purpose of security, but it also saves IP address space.

If every host on every network had to have real routable IP addresses, we would have run out of IP addresses. But by using private IP addresses, ISPs, corporations, and home users only need a relatively tiny group of bona fide IP addresses to connect their networks to the Internet.

To accomplish this task, we need using  something called Network Address Translation (NAT)(discussed later)

The reserved private addresses are listed in Table 2.5.that you must know

Broadcast Addresses

Layer 2 broadcasts These are sent to all nodes on a LAN.

Broadcasts (layer 3) These are sent to all nodes on the network.

Unicast These are sent to a single destination host.

Multicast These are packets sent from a single source and transmitted to many devices on different networks.

First, understand that layer 2 broadcasts are also known as hardware broadcasts The broadcast  would be all 1s in binary, which would be all Fs in hexadecimal, as in FF.FF.FF.FF.FF.FF.

Then there’s the plain old broadcast addresses at layer 3. Broadcast messages are meant to reach all hosts on a broadcast domain. These are the network broadcasts that have all host bits on. Here’s an example that you’re already familiar with: The network address of 172.16.0.0 255.255.0.0 would have a broadcast address of 172.16.255.255—all host bits on.

Broadcasts can also be “all networks and all hosts,” as indicated by 255.255.255.255. A good example

of a broadcast message is an Address Resolution Protocol (ARP) request.

A unicast is different because t’s directed to a specific host. A DHCP client request is a good example of how a unicast works. Here’s an example: Your host on a LAN sends out an FF.FF.FF.FF.FF.FF layer 2 broadcast and 255.255.255.255 layer 3 destination broadcast looking for a DHCP server on the LAN. The router will see that this is a broadcast meant for the DHCP server because it has a destination port number of 67 (BootP server) and

will forward the request to the IP address of the DHCP server on another LAN. So, basically, if your DHCP server IP address is 172.16.10.1, your host just sends out a 255.255.255.255 DHCP client broadcast request, and the router changes that broadcast to the specific destination address of 172.16.10.1. (In order for the router to provide this service, you need to configure the interfaces with the ip helper-address command—this is not a default service.)

Multicast is a different , it appears to be a hybrid of unicast and broadcast.

Multicast does allow point-to-multipoint communication, which is similar to broadcasts, but it happens in a different manner. it enables multiple recipients to receive messages without flooding the messages to all hosts on a broadcast domain.

Multicast works by sending messages or data to IP multicast group addresses. Routers then forward copies (unlike broadcasts, which are not forwarded) of the packet out every interface that has hosts subscribed to that group address.

There are several different groups that users or applications can subscribe to. The range of multicast addresses starts with 224.0.0.0 and goes through 239.255.255.255. As you can see, this range of addresses falls within IP Class D address space based on classful IP assignment.