![]() ![]() If the test fails then grep did not find either of the strings, meaning the ARP request failed. If it is, it uses echo to print a message of success to the terminal window. The if statement tests $?-a variable that holds the exit code of the last process that ended-to see if it is zero. When you know which of the phrases your version of arping uses, you can simplify the grep syntax by removing the other phrase. If grep finds either of these phrases, its exit value will be zero. grep is looking for one of two strings, either "1 response" or "1 packets received." This is because the test computers had different versions of arping on them and they use different terminology. The grep syntax can be simplified in your script. The output from the arping command is piped through grep. The script uses the same arping -c format we've already seen, but this time we're only asking for a single ARP request to be sent to each device in the range. At each spin of the for loop, $device is set to the next IP address in the range. The parameters are accessed inside the script as $1 and $2. 20 and would terminate after using IP address 192.168.1. So, if you pass 20 and 30 to the script, the loop would begin at 192.168.1. These are used as the last octet of the IP addresses of the range you want to use arping on. The script accepts two command line parameters. You'll need to edit the script and replace all occurrences of 192.168.1 with the IP address of your network. Copy the text from this script and save it to a file called "scan-range.sh." The radio waves used in Wi-Fi would also fall into this category.īy wrapping arping in a loop in a script, we can get it to work over a range of IP addresses. This is concerned with the physical infrastructure including cabling, routers, and network switches. It is used to send packets between directly-addressable devices using broadcasts to every device or unicasts to specific MAC addresses. It's the layer that the Internet Protocol-the IP in TCP/IP-operates at. This is where routing and packet forwarding takes place. The Transmission Control Protocol-the TCP in TCP/IP-operates at this layer. This layer is concerned with such things as transfer rates and data volumes. This is the layer that moves data around the network in a coordinated way. This layer involves itself with such matters as the initiation of a connection, handshaking, timeouts, and the breaking of connections that are no longer required. A session is a network connection between two or more devices. Encryption and decryption take place at this layer. This makes sure the data is in the right format or state as it moves to and from the network format. It provides information to the computer user and receives information back from them. Layer 7 is the top-most layer, the application layer.Higher layers cannot operate without the lower layers. The Open Systems Interconnection model groups the technologies that make up a working network as a series of layers. But because the IP address on its own isn't enough information to route packets to the device, the Catch-22 is it can't use the IP address to query the hardware to get the MAC address. ![]() The router needs to obtain the MAC address which is the missing piece of the jigsaw. When a new device is connected to your network it is assigned an IP address, but that isn't enough to actually route traffic to it. If the router needs to route data to a device it doesn't know about, it makes an ARP request to obtain the MAC address for the new device. ![]() The device responsible for marshaling and directing network packets in your network-usually, the router-builds and maintains an ARP table that ties IP addresses to MAC addresses. The Address Resolution Protocol is the middleman that maps IP addresses to MAC addresses. The MAC address is a unique identity established at the point of manufacture of a device. To be able to correctly route network traffic to the appropriate device, a scheme has to be employed that maps IP addresses to Media Access Control (MAC) addresses. That is, their IP address might well change the next time they're booted up. But most devices on local area networks have dynamic IP addresses. It's used as an address so the appropriate network traffic arrives at the correct device. An IP address is a numerical label for a networked device. ![]()
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