How to scan for IP addresses in a local network

Published by on August 13, 2018 in Net Admin

How to scan for IP addresses in a local network

If you’re new to network administration and want to find out what IP addresses are allocated to the devices connected to your network, there is a simple operating system command that will tell you everything you need to know.

By default, each device gets a network IP address by automated processes, so you don’t actually need to set up the connection or type in an address when you connect a computer, a printer, or a VoIP handset to the network. This automation is great, but sometimes you need to know those addresses. When you experience network problems, there are steps that you can take in order to investigate and solve the problem. Therefore, you are probably going to need to know the addresses of your equipment so that you can identify the device that is the cause of the problem.

The quickest, simplest tool will give you a bare list of IP addresses, but then you will need to find other tools in order to investigate further or fix problems. So, you will soon find that it is probably better to get a network administration tool to help you monitor and manage your network. As your system grows, you will have to get a network monitor in order to keep on top of the increasingly complicated network.

In this guide, you will learn about a quick way to find out the IP addresses on your network, and then you will read about some basic tools that will get that information in a more digestible format and give you options to manage addresses.

Quick list of IP addresses

In order to get a list of the IP addresses of all of the devices connected to your network. Follow these steps:

  1. Open a terminal window to get to the command line.
  2. Issue the command ipconfig and press Return. On Linux type ifconfig instead.
  3. Enter the command arp -a to get more information.

Analyze investigation results

The ipconfig command will return a set of results for each of the network adapters that you have set up on your computer. Those adapters that are not active will show the result, Media disconnected, so you can ignore those.

You need to look for adapter results that show IPv4 Address and Default Gateway entries.

ipconfig results

You now have the addresses of two devices on your network. The IPv4 address is the network address of the computer that you are using, and the default gateway result is the IP address of your router.

The ARP results will give you a list of all of the allocated addresses on your network.

arp results

If you see several batches of results, look for the one that has the IP address that was reported as your computer’s IP address in the ipconfig results. The list of IP addresses that you see below that shows all of the other addresses that have been allocated on your network. So the complete list is all of these addresses including the address of your computer.

In the ARP results shown above, you can see four addresses that are labeled dynamic and six addresses that are categorized as static. If you have not made any intervention at all to allocate addresses manually to devices on your network, then all of the physical pieces of equipment will have dynamic addresses. The static addresses are used for administration by your router. The first address in the list is the address of your router. This should match the Default Gateway address that you saw in the ipconfig results.

In the illustrations in this section, you can see that the ipconfig and arp commands have revealed the address of the router, the address of the computer from which the commands were issued, and the network addresses of four more devices that are connected to the network.

Improved IP scan results

An IP address scanner is just going to give you more or less the same information that you got from the arp command. There are a few IP address scanner tools that can add on a little extra information and present them in a more attractive format. A good scanner tool should also allow you to save results to a file so you can compare IP address usage over time or reconcile address usage with your DNS server and DHCP server if you get to the point where these functions are managed away from the router.

Most IP address scanners just add a front end to that arp command you tried yourself. An alternative method uses a utility called Ping and runs the command repeatedly to see which addresses respond. This category of software is called a Ping sweep tool.

To give you an idea of the type of information you can get from an IP address scanner or a Ping sweep tool, take a look at these two tools:

Angry IP Scanner

Angry IP Scanner

This free IP scanner can be installed on Windows, Linux, and Mac OS. The scanner expects a range of IP addresses as a parameter to the search, but if you just enter a very wide range, you don’t need to worry about seeing a list of unused addresses because the tool will only show addresses that are in use.

The output of a scan shows the IP Address of each device on the network, together with the hostname and the contact response time. You also have the option to see each device’s MAC address and a list of its open ports. Output can be saved to text, CSV, or XML formats.

SolarWinds Ping Sweep (FREE TRIAL)

SolarWinds Ping Sweep

To get a look at how a Ping sweep tool operates you could try out the SolarWinds Ping Sweep function. The tool works on Windows and it has a graphical interface. You need to enter an address range before starting the sweep. The results of a sweep show each IP address in use, the host name of that device and the response time for that node. You can save results in text, CSV, or HTML format.

Unfortunately, this tool is not free. It is part of a very large bundle of more than 60 tools, called the Engineer’s Toolset. The toolset is a bit pricey, but it is packed with all of the network administration tools that you are going to need. You can try out the package in a 14-day free trial.

SolarWinds Engineer's ToolsetDownload FREE Trial at SolarWinds.com

FURTHER READING: 10 Best Ping Sweep Tools and Software

IP Address Tracker tools

One level up from scanning is tracking. An IP tracker will spot when an allocated IP address gets dropped or becomes unresponsive. This situation is very rare on a small network, but once you install a separate DHCP server, dropped or changed IP addresses start to become a big issue. If you try allocating your IP addresses yourself without a server, you are going to end up with duplicate addresses and DNS errors, so things can really get out of hand very quickly without a tracker.

Here are two IP address tracker option for you to look into.

SolarWinds IP Tracker (FREE DOWNLOAD)

SolarWinds IP Tracker

SolarWinds gives a much better deal with its IP Tracker than it does with its Ping Sweep tool, because this standalone utility is completely free of charge. The software installs on Windows.

This tool is able to spot IP address misallocation that results in duplications. One shortfall of the service is that it isn’t able to coordinate directly with a DHCP server or a DNS server. However, that functionality is only usually expected from an IP address manager and the SolarWinds IP Address Manager covers all of those duties if that is the type of coverage that interests you.

SolarWinds IP Address ManagerDownload FREE Trial at SolarWinds.com

 

MyLANViewer

MyLanViewer

MyLANViewer is free to use and runs on Windows. The tool scans the network and then lists all of the devices that it discovered in a GUI interface. The list is organized a little like a Windows Explorer directory structure. Each node in the results list can be expanded to show the device’s IP address, MAC address, operating system, work group, and Ping time.

This tool keeps its eye on the system and will notify you if a new device connects to the network. It can also detect hidden devices and rogue DHCP servers. So, this ongoing monitor of IP addresses acts as a security tool.

FURTHER READING: 10 best IP address tracker tools and software

IP address management

Large networks require IP address management systems to reconcile DHCP and DNS records with the reality of the IP addresses that are actually in use on a network. Network IP scanning is the basic element of IP management. If you are just starting up a new, small network, IP address scanning should be all you need. As your network grows, however, you will need to advance to IP address tracking and on to using an IP address manager.

FURTHER READING: The Definitive Guide to DHCP

Image: My IP address by Collin Anderson via Flickr. Licensed under CC BY-SA 2.0

 

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