Most network administrators has to deal with many networking issues of slow network, DNS resolution etc. Also some time they have to find out newly connected devices IP address it has been allocated and how many IP address are consumed and which are free for communication. That’s why it is always a good idea to use network diagnostic tool for troubleshooting problems or finding the answers to complex questions.
Not surprisingly, plenty of options exist in the open source, but don't waste time on the trying these software one by one to find out one who will fulfill your requirement. Here are the list of best free network analysis and diagnostic tools for network admin-
Nmap is an open source tool for network exploration and security auditing. It includes many port scanning mechanisms (both TCP & UDP), OS detection, version detection, ping sweeps, and more. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics.
Nmap is commonly used for network inventory, managing service upgrade schedules, and monitoring host or service uptime. You can also check if there are any devices connected on your network without your knowledge.
The output from Nmap is a list of scanned targets, shows the list of port number and protocol, service name and stat in “port table” The port table may also include software version details when version detection has been requested. When an IP protocol scan is requested, Nmap provides information on supported IP protocols rather than listening ports.
In addition to the interesting ports table, Nmap can provide further information on targets, including reverse DNS names, operating system guesses, device types, and MAC addresses.
Wireshark is the famous, an open source network monitoring and analysis tool that lets you see what's happening on your network at a microscopic level. It is capable to analyze network traffic on any size network and it is available for UNIX and Windows. Wireshark can capture traffic from many different network media types - and despite its name - including wireless LAN as well.
Captured network data can be browsed via a GUI, and it has powerful display filters to see just what you want.
You can use Wireshark to it to troubleshoot network problem, to examine security problems, to debug protocol implementations, to learn network protocol internals.
3) Zenoss Core:
Zenoss Core is the powerful open-source monitoring tool that offers visibility over the entire IT stack, from network devices to applications.
It has web based customizable console and dashboards, and it’s interface is efficient and intuitive. It include fault and event monitoring and management. Here you can monitor and manage the performance and availability of all devices in your IT infrastructure (network, server, storage, applications, converged infrastructure, virtualization/cloud), configuration, performance, and events. It shows reports for devices, events, performance, and performance graphs and these report can be export and scheduling.