Command Line Utilities for Troubleshooting DNS | ISGMLUG

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Command Line Utilities for Troubleshooting DNS

There are of course, many tools for configuring, installing and troubleshooting DNS issues, many can make life an awful lot easier.   Anyway here’s some of the perhaps most popular ones which exist in various platforms.

nslookup

This utility is probably the oldest and most widely used DNS tool available.  IT’s primary functions are to run individual and specific queries on all manner of resource records.  It is even possible to perform zone transfers using this tool, which is why it’s so important.

ipconfig

This tool is often used daily to release and renew DHCP addresses.  However it can also be used to perform some DNS functions, it’s certainly a useful client tool to get to grips with. There are a couple of very useful switches which supply DNS related functionality.  The /displaydns switch will return the contents of the client resolver cache.   It will show you the Record Name, TYpe TTL, Data Length and RR Data.  It will use cache data to return these records at least until the TTL expires when it will query a name server.  The /flushdns switch is used for erasing the contents of the resolver cache.  In troubleshooting terms this means that cached data will not be used and a fresh request will be sent to a name server.   Finally /registerdns which will refresh it’s DHCP lease and network records.

netdiag

One of the most useful general diagnostic tools you will find in a Windows environment.  It performs a long list of network connectivity tests, including a specific DNS test.   Using the switch /test:DNS the program will check each active network card and see whether it has a A record registered in the domain.  The additional switch /DEBUG can be used in conjunction with this to produce a verbose output to the screen which is extremely helpful in troubleshooting DNS issues.  It can be found in the Windows support tools directory which is on the installation disks and shares.   It’s surprisingly useful when checking a DNS service or programs.

dnsdiag

This useful utility is especially useful in checking through email issues that are DNS related. A DNS misconfiguration can cause all sorts of email issues as many have experienced.   It functions by simulating all the DNS related activities which would be done by an SMTP agent when delivering email  There is a caveat in it’s use for this sort of diagnostic work, you’ll need to run it on a computer which has either and Exchange or SMTP agent installed locally.

Most of these tools can be used to solve a huge range of DNS related issues, so they’re worth getting to grips with.  A great test is to use them with a new installation, or DNS design, perhaps run through the tools to check out that DNS is working properly.

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