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April 4, 2007

5 Things I Hate about the Cisco IOS (and How to Fix Them!)


No matter what operating system or networking platform you use, there will always be things that you just can’t stand about it, right?

I have been using the Cisco IOS for many years and came up with 5 things that I hate. But I am going to do more than show you what I don’t like; I am going to show you how to fix these things! Take a look…

1. Automatic DNS lookup – what a pain!

The Cisco IOS, by default, comes with a “feature” where any unknown command you type at the command prompt, is automatically considered a host on the network that you want to telnet to.

The IOS then attempts to contact a DNS server by broadcasting to the IP address. It attempts this 3 times and has some kind of time-out of about 10 seconds per broadcast.

Thus, for your mistake in typing, you are “penalized” with a 30 second time out, where you cannot type any commands. This can be a real pain! Here is what it looks like:

Fix Cisco IOS

To resolve this, you just need to enter one simple global configuration mode command- no ip domain-lookup, like this:

Fix Cisco IOS

2. Interrupting my commands! Argh!

Say that you are typing a command and you are on the router’s console. Many times, you are in the middle of a command and a console logging message pops up, right in the middle of your command. You don’t know where you were in the command or how much you have typed. You don’t know what to do. Do you press enter? What did you type? Can you delete backwards? How frustrating! Here is what it looks like:

Fix Cisco IOS

As you can see, I was typing “show running-config” and in the middle of the command, I was interrupted with a console logging message. To resolve this, you use the logging synchronous command on each telnet line and your console port. Here is how you configure it:

Fix Cisco IOS

3. Not saving my configuration for me! What was that command again?

Say that you have spent an hour configuring your new router, but all of a sudden your router loses power. When you reboot, all your configurations are gone! Guess what, the IOS doesn’t save any configuration changes automatically. You have to save your own changes so make sure you save, and save frequently! The textbook method to save your configuration is copy running-config startup-config. However, the easiest way is to just type wr. Take a look:

Fix Cisco IOS

With the wr command, your config is saved quickly and easily. Now, you just have to remember to type it every few configuration changes you make.

4. The Router’s log date & time is wrong, why do I have to keep setting the clock?

You do a show logging to see the router’s log file and the date and time are wrong. It’s not like they are a little bit off; the problem is that the router thinks that it is March 1, 1993, about midnight.

Fix Cisco IOS

The date and time of March 1, 1993 at midnight are important. These are the default date and time. This means that the router has just booted and has no time source. Routers don’t have an internal clock, unlike a PC. Router’s don’t save their date or time when they are rebooted or powered off.

The best way to resolve this is to have a NTP (network time protocol) server on your network. This way, when the router boots up, it will automatically find out the proper date and time. To do this, you would use the ntp server x.x.x.x command. Here is how you configure it:

Fix Cisco IOS

NOTE: Prior to this, you should configure your router’s time zone using the clock timezone command.

5. What was that command? There are SO many commands!

The Cisco IOS has thousands of commands and command combinations. How can you remember them all? Chances are you probably cannot. The answer to this is to use the question mark at every point in your command sequence.

Say that you are trying to set the clock on a router. Maybe you cannot remember the command do to this at all. To see a list of commands, you type ?, like this:

Fix Cisco IOS

By doing the ? command, you find out that the command to set the router’s clock is clock, but then what do you type? To find out, type clock ?, like this:

Fix Cisco IOS

Now you know that you should type clock set, but then what? Use the ? again and just keep doing this until you have completed the whole command. Here is an example:

Fix Cisco IOS

Success! Using the ?, guides you through setting the router’s clock. Using the question mark is very helpful to both beginners and experts in configuring your router successfully.

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Cisco BSCI

In Conclusion

The Cisco IOS has its fair share of annoyances, but knowing how to fix them can make the difference between getting the job done, or failing to do the job at all. Knowing how to fix them also means the difference between great frustration and successful configuration. In this article, you learned the 5 things that drive me nuts, and how to fix them.

About the author:

David Davis (CCIE #9369, CWNA, MCSE, CISSP, Linux+, CEH) has been in the IT industry for 15 years. He currently manages a group of systems/network administrators for a privately owned retail company and authors IT-related material in his spare time.

He has written over one hundred articles, eight practice tests and three video courses and has co-authored one book.

About the Author

is a CCIE, vExpert, VCP5, and VCAP-DCA. He has been in the IT industry for 20+ years and is the author of hundreds of articles and videos. He has created over 10 TrainSignal video training courses including the numerous courses that make up the best-selling VMware vSphere video training library.

Author's Website: