by Tony Mattke on June 9, 2010
Learning the particulars of Cisco IOS is one of the most valuable things a network engineer can do. These skills will be the basis of everything you do on the lab and on your network. The following is a collection of things that most everyone uses these days.
Prevent timeout on the serial console. You can also apply this to the VTY lines if you ssh / telnet into the router.
Router(config)#line con 0
Router(config-line)#exec-timeout 0 0 ! 0-minutes 0-seconds
The following configuration will allow you to work uninterrupted from system messages.
Router(config)#line con 0
Router(config-line)#logging synchronous
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by Tony Mattke on November 23, 2009
This is one of those tricks you wish you learned about 10 years ago, but never did. You know how easy it is to mess up a nice looking access list. You get one setup on the router, and then you end up tinkering with it over the next month and the next thing you know you have the ACL that fell out of the ugly tree and hit every branch on the way down. I have the same issue, actually the other day I was working on some ACLs for a clients VPN configuration when I realized I had forgot to include some entries. So after adding what I needed, I ended up with something like this… ( IP address have been obviously changed to protect the innocent. Ok, honestly, the whole example is just hog wash. I’m way too lazy to actually go lookup the ACL I was working on. )
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by Tony Mattke on July 19, 2009
How many times a day do you issue a show command from configuration mode ? If you’re anything like me, its enough to get annoying. Luckily Cisco has given us the ability to user define aliases, here is a simple solution to this issue.
router(config)#<b>alias configure show do show</b>
While this fixes part o fthe issue, you’ll need to configure additional aliases for each configuration mode that you wish to use this in. I would certainly at least setup interface and router. Are there any handy alises you use every day? Comment below to share them with us!
by Tony Mattke on June 8, 2009
Ever accidentally set your config register to a random value that isn’t in the Cisco documentation? No? Neither have I, but one day I encountered someone on #cisco that had. So I did my best to help him, and was able to decode his settings and get him back into the CLI.
First things first. Lets hope you remember the value you entered, or else you’re going to be trying every bit rate.. If you do, convert it to decimal then binary, or straight to binary if you’re a badass. For example lets use 0×2121. Cisco has no reference of this in their documentation. Now that you can’t get into your router at the typical 9600 8,N,1…
- Convert 0×2121 to decimal………….. 8481
- Convert 8481 to binary…………………. 10000100100001
- Insert this number into the table below… Top->Bottom; Right->Left
I’ve filled in the values on the far left column.
- You’ll notice our values for the console line speed rows exactly match that of the 19200 column.
Thats it ! Fire up your console at 19,200 baud and you’ll be set…
I hope this helps someone out, if you do have any questions, please feel free to ask.
by Tony Mattke on May 27, 2009
So, I’m sure these have been posted almost on every networking blog under the sun, but who knows, right? Here are a few tips and tricks to help you move around the IOS a bit faster, find information faster, and locate problems… faster.
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