Hi, Today lets check, The cisco command line basics

1.The “?”

You can use the command in many ways. First, use it when you don’t know what command to type. For example, type at the command line for a list of all possible commands. You can also use it when you don’t know what a command’s next parameter should be.

2. show running-configuration

The show running-config command shows the router, switch, or firewall’s current configuration. The running-configuration is the config that is in the router’s memory. You change this config when you make changes to the router. Keep in mind that config is not saved until you do a copy running-configuration startup-configuration. This command can be abbreviated?sh?run.

3.?show interface

The?show interface?command displays the status of the router’s interfaces. Among other things, this output provides the following:

• Interface status (up/down)
• Protocol status on the interface
• Utilization
• Errors
• MTU

4.?no shutdown

The?no shutdown? command enables an interface (brings it up). This command must be used in interface configuration mode. It is useful for new interfaces and for troubleshooting. When you’re having trouble with an interface, you may want to try a?shut?and?no shut.

5. show ip route

The?show ip route?command is used to show the router’s routing table. This is the list of all networks that the router can reach, their metric (the router’s preference for them), and how to get there.

6. show version

The?show version?command gives you the router’s configuration register (essentially, the router’s firmware settings for booting up), the last time the router was booted, the version of the IOS, the name of the IOS file, the model of the router, and the router’s amount of RAM and Flash. This command can be abbreviated?sh?ver.

7. debug

The?debug?command has many options and does not work by itself. It provides detailed debugging output on a certain application, protocol, or service. For example,?debug ip route?will tell you every time a router is added to or removed from the router.

SOME BASIC THINGS BEFORE STARTING CCNA !

Lets Exercise

ping :– packet internet gopher it uses icmp ( internet control message protocol)? protocol For verification the other device is reachable to me or not?? ipconfig :– to check the ip address of a computer ipconfig /all :– to check the ip address + mac address getmac :-? to check the mac address of a computer ?netstat :– to check the session’s nslookup :– to check the all servers of a website arp -a? :– to check arp table arp ?d :– to delete arp table ( run as administrator) ? TO check public ip ? Visit :– www.whatismyipaddress.com? to check your public ip ??????????? ? To assign address to your PC ? 1.windows button +? R??? 2. type? ?ncpa.cpl? to go to your network connections 3 choose your lan adapter and go to properties and click on IPV4 HUB

• ALWAYS do Broadcast
• Layer 1 device
• Shared bandwidth
• Less no of ports
• Doesn?t learn mac address?

SWITCH

• which connects two or more computers together
• Many no of ports
• Learn mac address
• Two types of switch :-
• Manageble switch and unmanageable switch
• Layer 2 devices, datalink layer ( mac address )

ROUTER:

• It is an internetworking device used to connect two or more different networks
• It works on layer 3 i.e. network layer
• It Performs Routing

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Related articles across the web

• Network Basics: The Definition of a Static IP Address
• Why are ARP queries sent in a broadcast frame? Why is the response sent with a specific destination MAC address?
• Understanding Public IP Addresses
• Layer 2 ARP spoofing attack
• Troubleshooting

Loopback?(loop-back) refers to the routing of electronic signals, digital data streams, or flows of items back to their originating devices or facilities without intentional processing or modification. This is primarily a means of testing the transmission or transportation infrastructure.

Example applications:

• A communication channel with only one?endpoint. Any message transmitted by such a?channel?is immediately and only received by that same channel.
• Performing?transmission?tests of?access?lines from the serving?switching center, which usually does not require the assistance of personnel at the served terminal.
• Testing between stations (not necessarily adjacent) where in two lines are used, with the test being done at one station and the two lines interconnected at the distant station. Commonly called?loop around?when the interconnecting circuit is accessed by dialing.
• A?patch cable, applied manually or automatically, remotely or locally, that facilitates a loop-back test.

Checksum and CRC

Another secure-computing need is to ensure that the data has not been corrupted during transmission or encryption. There are a couple of popular ways to do this:

Checksum– Probably one of the oldest methods of ensuring that data is correct, checksums also provide a form of authentication because an invalid checksum suggests that the data has been compromised in some fashion. A checksum is determined in one of two ways. Let’s say the checksum of a packet is 1 byte long. A byte is made up of 8 bits, and each bit can be in one of two states, leading to a total of 256 (28?) possible combinations. Since the first combination equals zero, a byte can have a maximum value of 255.

• If the sum of the other bytes in the packet is 255 or less, then the checksum contains that exact value.
• If the sum of the other bytes is more than 255, then the checksum is the remainder of the total value after it has been divided by 256.

Let’s look at a checksum example:

• Bytes total 1,151
• 1,151 / 256 = 4.496 (round to 4)
• 4 x 256 = 1,024
• 1,151 – 1,024 = 127 checksum

Cyclic Redundancy Check (CRC) – CRCs are similar in concept to checksums, but they use polynomial division to determine the value of the CRC, which is usually 16 or 32 bits in length. The good thing about CRC is that it is very accurate. If a single bit is incorrect, the CRC value will not match up. Both checksum and CRC are good for preventing random errors in transmission but provide little protection from an intentional attack on your data. Symmetric- and public-key encryption techniques are much more secure.

All of these various processes combine to provide you with the tools you need to ensure that the information you send or receive over the Internet is secure. In fact, sending information over a computer network is often much more secure than sending it any other way. Phones, especially cordless phones, are susceptible to eavesdropping, particularly by unscrupulous people with radio scanners. Traditional mail and other physical mediums often pass through numerous hands on the way to their destination, increasing the possibility of corruption. Understanding encryption, and simply making sure that any sensitive information you send over the Internet is secure (remember the “HTTPS” and padlock symbol), can provide you with greater peace of mind.