Author Profile - Tony Fortunato is a Senior Network Specialist with experience in design, implementation, and troubleshooting of LAN/WAN/Wireless networks, desktops and servers since 1989. His background in financial networks includes design and implementation of trading floor networks. Tony has taught at local high schools, Colleges/Universities, Networld/Interop and many onsite private classroom settings to thousands of analysts. Tony is an authorized and certified Fluke Networks and Wireshark Instructor. His Pine Mountain Group CNA Level I and II certification demonstrates his vendor neutral approach to network design, support and implementations. Tony has architected, installed and supported various types of Residential Wireless High Speed as well as hundreds of WIFI hotspots. Tony uses a variety of technologies from Powerline, Wireless and wired technologies to find the most cost-efficient and reliable solution for his customers. Tony combines custom programs, open source and commercial software to ensure a simple support infrastructure.
The other day in my office, my Office Manager, Sue exclaims, "The internet is down!!".
I love saying this to my customers, "I'm off to fix the Internet". (Picture me in a red cape and yellow tights, then send you therapy bill to Lovemytool ;b ).. Sorry, I digress.
Like all technical people, I start my testing from my laptop and quickly conclude I'm fine and have no issues browsing, checking my email, printing, or accessing the server. So obviously the problem is with Sue's computer - simple, closed case, correct? WRONG!!!!
Now I do the unthinkable. Something I rarely see any PC or Network Technician do. Something so daring it is bordering on just plain 'crazy'. I walk over to the person having the issue to see what they are complaining about to see the problem for myself. Yes I know, real earth shattering 'meaning of life' material here folks.
I walk over and on Sue's Internet Explorer screen is the dreaded, "Internet Explorer cannot display the webpage" error message. I checked, and she was trying to go to Yahoo.ca. Strange, I was just on that same site with no issues. From her computer, I do the customary ping the server, router and printer with no issue. I ask if she has been able to get to any websites today and she says, "yup, and proceeds to show me several sites she was on, and can continue to access successfully.
Now I pull the standard technical response, "lets wait a bit and see if it clears" - Why do we say that??
After a standard reboot, no real change. How come that rarely works?
Actually there is a big change, now she can't access anything on the internet. And worse, I'm having issue accessing some websites. Now its personal! Time to dive in!!!!
I go back to Sue's computer and verify she can access all things local; server, printer, etc.. Then I try pinging our email server name and it fails. Well that's different.
I go back to my laptop and I can ping our email server by name. WHAT??!??? I try pinging another random site by name and it fails. A HA, now I can test from the comfort of my PC without hanging out with the icky client. YIPPEE!
Back to troubleshooting; so whats different? I realize that any sites I try to access for the first time, fails, anything I was currently on, is fine. I check my DNS cache via the 'ipconfig /displaydns' and can clearly see the sites that worked were cached. So I clear my cache with the 'ipconfig /flushdns' command and retest. BIngo, I can't surf or ping anything by DNS name anymore.
I start up Wireshark and try pinging my email server and got an interesting response, "server error" from both DNS servers. I also notice that I was using the new Google DNS server addresses, not the IP addresses provided by my ISP.
So from here, I simply used my ISP DNS server entries, and everything worked fine. Since I can't call Google technical help desk, I stay with my ISP's DNS entries.
In review, the DNS issue must have cropped up during the day, so anything we had cached in our PC's were fine since they did not require a DNS lookup, but anything to be looked up failed.
Total time spent 15 minutes.
Moral of the story;
- get off your butt and see the problem for yourself (when possible)
- use a consistent methodology when testing
- test and change ONE thing at a time
- measure the impact of your change or test
Bye for now.
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