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Network Troubleshooting I was helping someone troubleshoot a network problem last week. As it turned out, the problem was very physical: a light fixture had fallen down an loosened some connection to a switch. Both the existence and the location of that switch in relation to the rest of the network had vanished from institutional memory so much of the testing we were doing didn't make sense and was hard to interpret. In fact, it was so puzzling that I drove on-site with more sophisticated testing equipment, only to find that someone had noticed the fallen fixture before I arrived. Problem identified and solved, but it did prompt me to look for a general "Network Troubleshooting" page here and I was a bit surprised not to find one.

Title Date Comments
Kerio Connect won't start after updating SSL certificate   2015 04 
- How to quickly fix Kerio Connect if it cannot restart after updating or renewing its SSL certificate -
Missing attachments with Android Active Sync   2015 04 
- Attachments mysteriously disappeared when he sent email from his Android phone. He blamed the server, but was it that? -
Unable to browse the Internet   2015 04 
- Suddenly 15 PC's had trouble connecting to the Internet. Nothing had changed except they had been physically moved to another office. -
Debug SMTP Client or SMTP Server?   2015 03 
- When debugging Kerio Connect email problems, should you turn on SMTP Client or SMTP Server? -
Being confused can sometimes help   2015 03 
- If my customer's email hadn't been confused, I wouldn't have called him to help and he would have waited for something that was never going to happen. -
Increase IPsec debugging   2015 03 
- How to increase the Kerio Connect debug log verbosity for IPsec tunnels when you need to debug the connection. -
Kerio Control Speed Issues   2015 01 
- Test and resolve Kerio Control speed issues - is it the hardware or the scanning functions? -
Kerio Connect Mailbox alias could not be expanded   2015 01 
- What causes 'Mailbox alias could not be expanded' in the mailserver log files? -
Another SCO 5.0.7 crash   2015 01 
- Another SCO 5.0.7 crash tests my memory - it was taxing, but we got through it. A decade ago or more that would have been something I could fix while half awake, but now my memory of SCO Unix has truly faded. -
Ubuntu service start bug   2014 12 
- Ubuntu service start bug prevents restart of squid3 -
Using Antivirus programs with Kerio Connect   2014 12 
- Using Antivirus programs with Kerio Connect - Protecting Connect files from being corrupted by virus scanning. -
Kerio Control Certificate is not valid yet   2014 12 
- Kerio Control Certificate is not valid yet - what could cause that strange message? This really had me scratching my head. -
802.11g/n High Gain USB Wireless G / N Long-Range WiFi Network Adapter   2014 07 
- Boosting the very weak free wireless signal at our vacation home isn't easy -
Kerio Troubleshooting January 2014   2014 01 
- Looking at some Kerio related troubleshooting/support incidents from last month. -
Who's been reading my email?   2013 07  2013/07/02 DaveGillam
- The boss noticed that some emails he did not read were marked as read - who was responsible? -
An unusual DNS issue   2013 07 
- An unusual DNS issue threatens a paycheck - and I still don't know what went wrong -
Getting a list of recursive SPF records   2013 06  2013/06/28 TonyLawrence
- Should Kerio Connect have a function to automatically whitelist a valid SPF check? I think maybe they should. -
How to trouble-shoot file corruption   2013 07 
- If you don't have the space, you have to take running snapshots with fuser or lsof- that may not satisfy a very stubborn vendor who is convinced that *their* programs never screw up. -
Mysterious panics and freezes   2013 07 
- Crashes, panics and freezes: all work halts and you can't help being surprised. What just happened? -
Samepage - Redefining how people create and share information
Deleting a lost file name - delete unremoveable files   2013 07 
- It HAS a file name- it probably has control characters in it that are confusing the display. Try ls -b. If that doesn't work, do "ls -l > /tmp/t" and the "vi /tmp/t" -
View large files without more or less   2013 07 
- I have a rescue disk that doesn't include "more" or "less" - how can I examine large files? -
All about Telnet   2013 07 
- A collection of telnet related information and links. Telnet is seldom used today except for network troubleshooting. -
Pass-Through Printing   2013 07 
- The idea is that if the terminal sees a special key sequence, it will start sending the data out some other port (parallel or serial) until it sees some sequence that tells it to stop. -
Fixing an old SCO Unix 5.0.4 machine   2013 07 
- I found myself staring at an ancient Gateway and a screen hung at Enter run level (0-6, s or S) -
Wireshark 101   2013 05  2013/05/26 TonyLawrence
- Silly me. I really should have started using Wireshark long before this! -
Connect delete bug   2012 12 
- This is an unusual bug in the Kerio Connect 8 Web Client that few users are likely to see. -
Simple debugging with Kerio Control   2012 11 
- An easy way to use Control as a network sniffer by creating useless rules and adding Accounting logging. -
Understanding X-Loop forwarding headers   2012 11 
- How the X-Loop header works and how Cpanel apparently breaks it. -
Filtering and separating Kerio Control Debug logs   2012 10 
- Kerio debug logs can contain a lot of extraneous noise. Use a script like this to separate the wheat from the chaff -
Troubleshooting anti-spoofing messages   2012 10  2012/11/18 TonyLawrence
- Is this network congestion or some other problem? Can you see what is confusing me? Join me in a network troubleshooting problem. -
Troubleshooting Kerio Control installation   2012 10 
- Setting up Kerio control is usually very easy. If you do experience problems, this guide can help. -
Notes on Kerberos troubleshooting (Kerio)   2012 09  2012/09/18 TonyLawrence
- These are some notes on troubleshooting Kerberos, specifically in the context of Kerio directory service authentication. -
Kerio Connect crash dumps and the kassist Tool   2012 09 
- Kerio Connect crashes are rare, but if it does happen, this article will help you understand what to do. -
Moving an old SCO Unix Filepro box   2012 08  2012/09/18 TonyLawrence
- She thought she wanted to put a public IP address on this old SCO box. Fortunately, no one was able to help her with that. -
Setting up a multihomed Kerio Mailserver in a DMZ   2012 08 
- Missing a simple checkbox in the GUI network configuration prevented the mailserver from working in the DMZ -
Recovering from a bad Kerio Mailserver crash   2012 07  2012/09/17 TonyLawrence
- A RAID drive failure slowed the Kerio mailserver to a crawl and eventually brought it down entirely. More than 900 users without mail - what now? -
Query Kerio Custom rules   2012 07  2012/07/23 TonyLawrence
- A script to query Kerio mailserver custom rules or list by type. Partially useful on Windows with Perl or Cygwin. -
Fixing excessive user whitelisting   2012 07 
- A beta script for correcting unwanted entries in users Spam whitelist. A problem can arise when users whitelist people within their own organization. That's usually unnecessary because spam tests are normally not applied to "trustworthy relay agents" -
Failure of encrypted connection Kerio Mailserver   2012 07  2012/07/20 TonyLawrence
- An unexpected cause to a failure to receive email from a customer momentarily baffles me. -
Kerio Troubleshooting   2012 05  2014/07/03 TonyLawrence
- There are only a very few things that will completely prevent Kerio Mailserver from starting. Usually this would come from a confused or mangled configuration file, but there are other conditions that can cause Kerio to refuse to start. -
Android phone crashes email account   2012 05  2012/05/18 Kanti
- A misbehaving Android phone caused a user to send duplicate messages - hundreds of them. We stopped that quickly by deleting her account on the phone (it's easy to recreate), but two weeks later her email stopped working -
Kerio Control Rip and Replace   2012 05  2014/07/10 TonyLawrence
- I tore out a perfectly good Astaro Firewall and replaced it with a Kerio Control box. The Astaro was only two years old and was working fine, but tearing it out made both me and my customer very happy. Read on to learn why. -
Support is not an annoyance   2012 05  2012/06/01 TonyLawrence
- Kerio's recent support changes have caused some customer backlash. I am sypathetic to some of these complaints, but I also see the necessity of the change and think it actually can be good for everyone. -
Troubleshooting Outlook KOC problems on new Windows 7 machines   2012 05  2015/02/07 anonymous
- Troubleshooting can lead us down strange paths. Join me as we watch new Windows 7 machines act up after joining a domain. -
A Kerio Firewall transplant causes mail problems   2012 04  2012/04/06 TonyLawrence
- Moving a Kerio Control firewall to new hardware shouldn't be any trouble at all. In fact, it was not, but some red herrings led me to think that something had gone mysteriously wrong. -
Troubleshooting a scanner with an email gateway   2012 03  2012/03/28 NickBarron
- After an email conversion, the only problem was a scanner that could not send email. That should have been a simple fix, but we were led far astray. -
Where is the boing? (Mac scheduled startup)   2012 03  2014/04/06 TonyLawrence
- I first noticed the missing Mac startup chime a few weeks ago. It seemed very odd that if I rebooted, the chime did work - it was only the first boot of the day when it did not "boing". Starting up took too long also - something was wrong, but what? -
iPad recovery mode problem caused by bad backup   2012 03  2012/03/12 TonyLawrence
- When my iPad started crashing Thursday night, it looked like bad hardware. I was even more sure of that when I tried to recover from a backup and it crashed doing that. I took it to the Genius Bar and they agreed, but we all were wrong. -
Mysterious Duplicate IP problem solved   2011 11  2011/11/14 NickBarron
- I only needed to be run over by four or five cluetrains before realizing what was causing this 'IP address conflict' message on a Windows 2003 server. Follow along and see when you solve it. -
Local printing in Synchronics   2011 11  2012/03/06 anonymous
- I know exactly what he has - an old SCO Unix system with a Digiboard multiport serial board, green screen Wyse terminals and Okidata printers with serial cards. I can handle all of that. -
Kerio Connect Mailserver
Do you hate your computer?   2011 09  2011/09/15 BigDumbDInosaur
- I knew someone who became so frustrated with a computer printer that he threw it down on the floor and jumped up and down on it until it was smashed to pieces. That's a bit extreme (and damaging to your bank account), but technology can make us feel like that, can't it? -
Basic Home Networking, Part 3, File and Printer Sharing   2011 08 
- The point of a computer network is sharing. You might not be sharing much, perhaps even only the Internet connection. If that's the end of it, you don't need much more than part one of this series, which deals with the setup of a basic small network. -
Putting the wrong name on a Win 7 user profile   2011 08  2011/08/25 NickBarron
- However, both of these new computer owners panicked at my suggestion. I explained that they just needed to cable up their new system; they claimed complete inability to do even that. Sigh. Yes, I know that this is mostly in their minds. It's a form of leaned helplessness. If they would just make a small effort, they probably could do this themselves, but they just stop and refuse to even try. It's too complicated, they are afraid that they might damage something or feel foolish. -
A few minor iPad set up problems baffle my neighbor   2011 08  2011/08/28 anonymous
- A neighbor took advantage of MA's recent tax free weekend and bought an iPad. He'd seen mine and his daughter had shown off hers the last time she had visited, so he had a pretty good idea of why he wanted it. Unfortunately, his initial experience was frustrating. -
Basic Home Networking - Part 2, wireless setup   2011 08 
- Often all that needs to be done is to tell your computer that you want to connect to a wireless network. It's not always that easy, but it certainly can be. However, even if it is that easy for you, you might still want to read the rest of this in case you have problems later. You also might want to read it because being "too easy" to get connected could mean that you are running some security risk and need to address that issue. -
Basic Home Networking - routers and switches   2011 08  2011/08/16 BigDumbDinosaur
- Setting up a small office or home network used to be a fairly complicated task. Aside from the technical knowledge needed, there was expensive equipment to buy and specialized tools for wiring. That's all changed - the necessary equipment is cheap and readily available and it's all very easy to configu re. -
A non-technical guide to understanding and fixing TCP/IP problems on a network   2011 08  2011/08/14 BigDumbDinosaur
- The title is a bit incorrect in the .non-technical. claim, because we are dealing with a geekish subject here and I can't avoid being a little "techie". -
Brother MFC-J615W printer   2011 08 
- I have never been a fan of inkjet printers. In fact. my general advice has been not to buy them because hey are far more expensive to operate than laser printer. These multifunction things have even more to dislike: if you lose part of the functionality, you are going to lose it all while it is out for repair. -
Perl Profiling with Devel::NYTProf   2011 07 
- I don't think I have ever used a profiler on my own code. The reasons are simple: I don't write much that is very complicated, so any bottlenecks are usually rather easy to spot. Most of what I do is ad hoc and limited use anyway, so speed is seldom a consideration. -

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