Networking Devices and Network Components

Networking devices are products used to connect networks. As computer networks grow in size and complexity, so do the networking devices used to connect them.

However, all networking devices share one or more common purposes.

1. They allow a greater number of nodes to be connected to the network. A node is an endpoint of a network connection or a junction common to two or more lines in a network. Nodes can be processors, controllers, or workstations. Nodes vary in routing and other functional capabilities; they can be interconnected by links, and they serve as control points in the networks. Node is sometimes used generically to refer to any entity that can access a network and is frequently used interchangeably with device.
2. They increase the distance over which a network can extend.
3. They localize traffic on the network.
4. They can merge existing networks.
5. They isolate network problems so that the problems can be diagnosed more easily.

The following networking devices broadly used in network.

1. Repeaters
2. Hubs
3. Bridges
4. Switches
5. Routers
6. Gateways
7. Modems
8. Network Interface Card (NIC)

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TCP/IP utilities | PING, TRACERT, ARP, Netstat, NBTSTAT/NetBIOS, IPCONFIG, NSLookup, WINIPCFG

Virtually every operating system with networking capabilities includes support for the TCP/IP protocols, and in most cases, the TCP/IP stack includes an assortment of utilities that enable you to gather information about the various protocols and about the network. Traditionally, these utilities run from the command line, although graphical versions are sometimes supplied. In many cases, a program uses the same syntax, even on different operating systems. This lesson examines some of the most common TCP/IP utilities and the purposes for which they are used.

• PING
• TRACERT
• Address Resolution Protocol (ARP)
• Netstat (Network Statistics)
• NBTSTAT/NetBIOS
• IPCONFIG
• NSLookup
• WINIPCFG

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Network Service | WINIPCFG

You can use the WINIPCFG utility to check a workstation's configuration details. For example, you can use the WINIPCFG utility to view the following information:

• Current host hardware address
• IP address
• IP address lease and renewal times (for DHCP-assigned address)
• Default gateway configuration

If your network is experiencing DHCP address problem, you can use the WINIPCFG utility's Renew/Renew All feature to force a workstation to attempt to renew an assigned address. When you this feature, however, the workstation release its IP address and cannot continue any IP-based operation.

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Network Support | NSLookup

The nslookup application can be used to interactively query servers running a domain name service (DNS) application. It will send domain name query packets to any designated DNS server Three data elements are required in order to formulate a DNS query using nslookup:
A DNS server name/address
. The Internet style address that is being queried
. The type of record you are searching for

NSLOOKUP is used to query the Internet name server in order to obtain an address if you have a site name or a site name if you have an address. It can be very useful as a quick check to see if an electronic mail address is, in fact, reachable. To translate a name to an address,
type NSLOOKUP site name

You should get a report like this:

NSLOOKUP spiderhunter.com
Server: LOCALHOST
Address: 129.0.0.1

Name: spiderhunter.com
Address: 38.10.0.4


To translate an address to a name, type NSLOOKUP address and you should see something like this:
NSLOOKUP 128.171.90.10

Server: LOCALHOST
Address: 128.0.0.1
Name: uIc.edu
Address: 128.171.90.10

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Network Support | IPCONFIG

When you run ipconfig at the Windows command line you see a display like this:

ipconfig Command

ipconfig [/? | /all | /release [adapter] | /renew [adapter]]

• /?  -- Display help message.
• /all  -- Display full configuration information.
• /release  -- Release the IP address for the specified adapter.
• /renew  -- Renew the IP address for the specified adapter.

The default is to display only the IP address, subnet mask and default gateway for each adapter bound to TCP/IP.

For Release and Renew, if no adapter name is specified, then the IP address leases for all adapters bound to TCP/IP will be released or renewed.

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Network Support | NBTSTAT / NetBIOS

Nbtstat.exe is a command-line program that displays information about the NetBIOS over TCP/IP connections that Windows uses when communicating with other computers on the TCP/IP LAN.

The syntax for Nbtstat.exe is as follows:

NBTSTAT [-a name] [-A ipaddress] [-c] [-n] [-r] [-RI [-s] [-S] [-RR]

• -a: name Displays the NetBIOS names registered on the computer identified by the name variable.
• -A ipaddress: Displays the NetB1OS names registered on the computer identified by the ipaddress variable.
• -c: Displays the contents of the local computer’s NetBIOS name cache.
• -n: Displays the NetBIOS names registered on the local computer.
• -r: Displays the number of NetBIOS names registered and resolved by the local computer, using both broadcasts and WINS.
• -R: Purges the local computer’s NetBIOS name cache of all entries and reloads the LMHOSTS file.
• -s: Displays a list of the computer’s currently active NetBIOS settings (identifying remote computers by name), their current status, and the amount of data transmitted to and received from each system.
• -R R: Sends Name Release requests to WINS, then starts Refresh.

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Network Support | Netstat (Network Statistics)

Netstat is a command-line program that displays information about a computer’s current network connections and about the traffic generated by the various TCP/IP protocols.
On UNIX computers, the program is simply called netstat, and on Windows computers, it is called Netstat.exe. The command-line parameters differ for the various implementations of Netstat, but the information they display is roughly the same.

The syntax for the Windows version of Netstat.exe is as follows:

NETSTAT [interval] [-a] [-p protocol] [-n] [-e] [-r] [-s]

interval: Refreshes the display every interval seconds until the user aborts the command.

• -a: Displays the current network connections and the ports that are currently listening for incoming network connections.
• -p: protocol Displays the currently active connections for the protocol specified by the protocol variable.
• -n: When combined with other parameters, causes the program to identify computers using IP addresses instead of names.
• -e: Displays incoming and outgoing traffic statistics for the network interface, broken down into bytes, unicast packets, non-unicast packets, discards, errors, and unknown protocols.
• -r: Displays the routing table, plus the current active connections.
• -s: Displays detailed network traffic statistics for the IP, ICMP, TCP and UDP protocols.

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Network Support | Address Resolution Protocol (ARP)

The Address Resolution Protocol (ARP) enables a computer to convert IP addresses to the hardware addresses that the data-link layer protocol need to transmit frames. IP uses ARP to discover the hardware addresses to which each  of its datagrams will be transmitted. To minimize the amount of network traffic ARP generates, the computer stores the resolved hardware addresses in a cache in system memory. The information remains in the cache for a short period (usually 2 to 10 minutes), in case the computer has additional packets to send to the same address.

Windows systems include a command-line utility called Arp.exe that you can use to manipulate the contents of the ARP cache. 

For example, you can use Arp.exe to add to the cache the hardware addresses of computers you contact frequently, thus saving a little time and network traffic during the connection process. Addresses that you add to the cache manually are static, meaning that they are not deleted after the usual expiration period. The cache is stored in memory only, however, so it is erased when you reboot the computer. If you want to pre-load the cache whenever you boot your system, you can create a batch file containing Arp.exe commands and execute it from the Windows Startup group.

Arp.exe uses the following syntax:

ARP [-a {ipaddress}] [-n ipaddress] [-s ipaddress hwaddress {interface} [-d ipaddress {interface}]

• -a {ipaddress} This parameter displays the contents of the ARP cache. The optional ipaddress variable specifies the address of a particular cache entry to displayed.
• -n ipaddress This parameter displays the contents of the ARP cache, where ipaddress identifies the network interface whose cache you want to display.
• -s ipaddress hwaddress {interface} This parameter adds a new entry to the ARP cache, where the ipaddress variable contains the IP address of the computer, the hwaddress variable contains the hardware address of the same computer, and the interface variable contains the IP address of the network interface in the local system whose cache you want yo modify.
• -d ipaddress {interface} This parameter deletes the entry in the ARP cache that is associated with the computer represented by the ipaddress variable. The optional interface variable specifies the cache from which the entry should be deleted.

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Network Support | TRACERT

You can use the TRACERT utility to determine the route that a packet may take to get from one device to another (if a route exists). You can also use this utility to determine the time that it takes the packet to reach routers and to identify Sluggish spots on the route.

The TRACERT utility uses interesting technology. If you analyze packets sent by the TRACERT utility, you will find that it uses the TTL counter to locate the route to another device.

When you run the TRACERT utility, it instructs the workstation to send a packet with a TTL count of 1 to the destination device. when this packet reach the local router, it discards the packet because the router cannot decrement the  TTL count to 0 and forward the packet. The router then sends an ICMP destination unreachable packet to the workstation.

This reply packet gives the workstation the IP address of the first router in the route. The workstation then send the same packet with a TTL of 2. The local router decrements the TTL count to 1 and forwards the packet.

The next router cannot decrement TTL count to 0 and forward the packet; so this router then sends an ICMP destination unreachable packet back to the workstation. This reply packet provides the IP address of the second router in the route.

The workstation continues incrementing the TTL count on each successive transmission until the workstation receives a reply back from the destination device.

you use the following syntax to launch  TRACERT utility:

TRACERT [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name

The parameter explain below:

• -d: Use this parameter if you do not want to resolve addresses to host names.
• -h: maximum_hops Use this parameter to determine the maximum number of hops to search for.
• -j: host-list Use this parameter to test loose source route along host list. This test specifies certain devices a packet must cross to reach a destination. this test does not specify the exact route, which can include other devices.
• -w: timeout Use this parameter to determine timeout milliseconds. Timeout determines how long the device waits for each reply. 

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Network Support | PING Command

You can use the PING utility to query another IP device on the network to determine if the IP device is “alive” and how long it takes a packet to reach the device. This utility is one of the first tools you should use if the problem appears to be caused by a lack of connectivity between IP devices. The PING utility uses Internet Control Message Protocol (ICMP) echo packets to perform tests on the network.

You use the following syntax to launch the PING utility:

PING [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] | [-k host-list]] [-w timeout] destination-list

The parameters are explained below:

• -t: Use this parameter to ping the host continuously. To stop this test, press <Ctrl>C.
• -a: Use this parameter to resolve addresses to host names.
• -n: count Use this parameter to determine the number of echo requests to send.
• -l: size Use this parameter to determine the ping packet size.
• -f: Use this parameter to set the Don’t Fragment flag on the packet. This flag ensures that the packet is sent to the destination device in its entirety. If you set this flag, routers will be unable to fragment the packet to cross media that support smaller packet sizes. If a route includes such media, a router discards the packet and sends an ICMP destination unreachable packet to the sender.
• -i: TTL Use this parameter to set the Time To Live (TTL) flag, which indicates the number of routers (hops) that a packet may cross. To limit the distance an ICMP echo packet can travel, you should define a small TTL value.
• -v: TOS Use this parameter to set the Type Of Service (TOS) flag. If the network has been configured to support, you can force the PING utility to use a specific type of service for the connectivity test.
• -r: count Use this parameter to record the number of hops to the destination IP device.
• -s: count Use this parameter to timestamp the hops.
• -j: host-list Use this parameter to test loose source route along host list. This test specifies certain devices a packet must cross to reach a destination. This test does not specify the exact route, which can include other devices.
• -k: host-list Use this parameter to test strict source route along host-list. This test specifies all the devices a packet must cross to reach a destination. The packet cannot cross other devices.
• -w: timeout Use this parameter to set the timeout in milliseconds. The timeout determines how long the IP device waits for a reply.

If a device is having problems communicating on the network, enter the following command at the DOS prompt: PING 127.0.0.1

The address 127.0.0.1 is the loopback address. If you enter this command, the device pings its own TCP/IP stack. if the device can’t see its own TCP/IP stack, the device can’t communicate on the network.

The Windows TCP/IP stack places an identifying pattern in each device’s ping packets. This identifying pattern, which is typically the alphabet, is located inside the ping packet padding area. You can use this identifying pattern to determine if a device is using the Windows TCP/IP stack.

You should not use the -t parameter unless you want to track and manually terminate the ping test. This parameter causes a continuous transmission of ping packets and may generate significant traffic on the network.

If you want to test the maximum packet size supported between two devices, use the -1 parameter (to define the maximum packet size) with the -f flag (to prevent the fragmentation of the packet). For example, if you wanted to know if you could send a 4 KB packet from a workstation to a NetWare 5 server in another building, you would enter the following command.

PING -f -l 4096 [destination]

You could then send the 4 KB packet to the server and find out if and where the packet would need to be fragmented.

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