Network Device And Ip

What is an IP address? Every machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this: •

216.27.61.137

To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. Look at the same IP address in binary: •

11011000.00011011.00111101.10001001

The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values! Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts. The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses: • •

• •

•

Default Network - The IP address of 0.0.0.0 is used for the default network. Class A - This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class. The other three octets are used to identify each host. This means that there are 126 Class A networks each with 16,777,214 (224 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. Class A networks account for half of the total available IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0. Net

Host or Node

115.

24.53.107

Loopback - The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing. Class B - Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (2 14) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (2 30) unique IP addresses. Class B networks make up a quarter of the total available IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet. Net

Host or Node

145.24.

53.107

Class C - Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also

include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet.

•

•

•

Net

Host or Node

195.24.53.

107

Class D - Used for multicasts, Class D is slightly different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class D accounts for 1/16th (268,435,456 or 228) of the available IP addresses. Net

Host or Node

224.

24.53.107

Class E - Class E is used for experimental purposes only. Like Class D, it is different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class E accounts for 1/16th (268,435,456 or 228) of the available IP addresses. Net

Host or Node

240.

24.53.107

Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address 255.255.255.255.

Subnet Mask Short for subnetwork mask, a subnet mask is method of dividing a network of IP addresses into groups. A common example of a subnet mask used is 255.255.255.0.

Netbits subnet mask

total addresses

/20

255.255.240.0

4096

/21

255.255.248.0

2048

/22

255.255.252.0

1024

/23

255.255.254.0

512

/24

255.255.255.0

256

/25

255.255.255.128

128

/26

255.255.255.192

64

last octet values

0, 128 0, 64, 128, 192

/27

255.255.255.224

32

0, 32, 64, 96, 128,

160, 192, 224 /28

255.255.255.240

16

0, 16, 32, 48, 64, 80,

96, 112, 128, 144, 160, 176, 192, 208, 224, 240 /29

255.255.255.248

8

0,8,16,24,32,40,48,56,64,

72,80,88,96,104,112,120, 128,136,144,152,160,168, 176,184,192,200,208,216, 224,238,240,248 The "last octet value" column defines the valid starting point for networks that have less than 256 addresses. For instance, if you are in network 128.174.5.x and have a network netbit of /28, then your subnet mask is 255.255.255.240. In this example x could take on the values of 0 or 16 or 32 or 48 or 64, etc. If you have been assigned the block of addresses starting at 128.174.5.48, then your range would extend to 128.174.5.63. This would give you a total of 16 IP addresses for your network. However, under this scenario, address 128.174.5.48 would be your network address, 128.174.5.63 would be your broadcast address, and typically 128.174.5.49 would be the address of your router. So in fact you have the ability to place 13 devices on your network (16-3). In another example, if your network is 128.174.5.0 and your subnet mask is 255.255.255.0 then you would think that you have the ability to place 256 devices on your network. However, the lowest address in your range defines your network, the highest is the broadcast address, and a third address (usually the second lowest) is reserved for the router. This means you have a practical limit of 253 devices (256-3=253) on your network.

Testing Connection using TCP/IP Usually, when connecting Windows systems, NetBEUI is used as network protocol, because the Microsoft "win95-server" (also called "Microsoft File and Print Sharing") can be most easily setup with NetBEUI protocol (you can also used TCP/IP or IPX/SPX, but that is a little more complicated) But when you think, that everything is setup properly, but you CANNOT get any connection, you need to establish first, what and where something is wrong in the complete setup:

whether the hardware (network board and cables) work properly to identify, whether you have a Hardware or Software problem. For that, the TCP/IP protocol supplied with Windows95/98/ME/NT4/2000 offers a small, but powerful tool called : 'ping'. (You can also use the NET DIAG test), allowing to make a connection test on a much simpler setup, but TCP/IP PING can also be used to test a WAN connections) :

"What is ping actually doing ?" Remember the movies on sub-marines, where they are searching each other sending out a search-signal , which sounds like 'ping' and where they get back an echo from another sub-marine ? That is EXACTLY, what the 'ping' utility does:

send out a signal

and get an echo back

That is part of any TCP/IP (regardless of the operating system): on receiving a 'ping', it sends the signal back to its origin.

Open a DOS-box, and on PC#1, typ: ping 192.168.10.2 This will send now an Ethernet package to the system with that IP-address, which is here PC#2. And every system properly configured with TCP/IP will send that packet back: the reply will be (for a test to IP-address 192.168.10.2 ) : Pinging 192.168.10.2 with 32 bytes of data: Reply from 192.168.10.2: bytes=32 time.......

If it comes back ("Reply from...") , then your Ethernet board and cables seem to be fine, you have a network software setup-problem, check the setup of the protocol (if IPX/SPX was used), check permissions and sharing, user- names and workgroup-names.

However, if the answer to your PING displays : Pinging 192.168.10.2 with 32 bytes of data: Request timed out.

'ping' did NOT get an answer back (' Request timed out'), try first if you can make the 'ping' from the other system (sometimes 'ping' works only in ONE direction, it may have been disabled on one system). If 'ping' does not work in both direction, then you have most probably a hardware problem, which could be the network board, the cable , the hub(if using 10baseT) or the t-connectors or the terminators (if using 10base2). (no joke: I know somebody, who went from Los Angelas to Hawaii just for that, he swapped a T-connector and then the network worked, checking later that t-connector showed a microscopic crack, not visible with the naked eye). If you are using a FastEthernet network, it could also be that the network card and the hub did not properly configure themself for the Media Speed and/or the Duplex-Mode. In professional networks, I would suggest now the use of Ethernet cable testers, which put a test-signal on the cable and can tell you, if the cable is o.k. or bad and then also WHERE is is bad.

Answer from PING: "Destination host unreachable"

This error message of PING indicates, that you tried to test the connection to a system NOT on the same subnet (where a direct connection is possible), but via a Gateway/Router on a different subnet (for more info on this issue, please see the section of Gateway/Router of TCP/IP-Bascis). But you did not define a Gateway address: :

When testing a TCP/IP connection via a Gateway/Router, you need to be aware about very single step: 1) The PING signal is send to the Gateway/Router (is the gateway defined ?)

2) The Gateway passes the PING signal on to the destination system (or if required to the next Gateway/Router, until it reaches it destination subnet)

3) The destination signal replies by generating the PING ECHO (is the destination system configured for the Gateway/Router, so that it is able to send back the signal ? )

4) The Gateway/Router receives the PING Echo and sends it back to the source-system:

When setting up Gateways/Routers, don't forget to setup ALL system, which the signal is traveling through from the source to the destination AND BACK. If "Ping" does not get back a reply from a connection via router(s), use the "tracert" command to find out, how far your test-signal got and where it got stuck. And if you have problems, enter the PING command on both systems, it may give you an error message indicating the problem (like a missing Gateway definition).