Category Archives: Technical Tidbits

Your ISP’s DHCP does not function properly

As part of my migration to the cloud, I terminated the Comcast Business internet service and switched to Xfinity internet.

When I initially signed up for the Xfinity service, I got their cable modem / router / wifi appliance. My plan was to get my own cable modem eventually because Xfinity charges $13 / month to lease the appliance.

I was at Best Buy and saw that cable modems weren’t expensive, so I decided to purchase a mid-level model (Netgear CM600) so I could save the lease fee. The CM600 would pay for itself in about 8 months.

It took a while to get setup … and there were a few false starts, but eventually I got it working connected directly to my MacBook.

I ran into a problem when I switched the CM600 over to my ASUS RT-5300 wifi router.

I kept getting the message “Your ISP’s DHCP does not function properly” on the ASUS network map page.

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Filtering mailing lists in Gmail

With my recent migration of servers from my basement to Amazon cloud servers, I had to rework how my email filtering was setup.

One of the challenges was how to handle the numerous mailing lists I participate in. Especially since I’m the list administrator for many of them.

After a bit of research, and experimentation, I found a pretty good formula for handling the filtering.

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whois

Here’s a tip for internet domain owners:

Make sure the contact information for your domain has more than one email address.  And make sure at least one of those email addresses is not in the domain itself.

If your email starts malfunctioning, you want people to be able to tell you about the problem … and if the only email addresses you list are in the actual domain, they won’t be able to contact you.

For example … if the mail server for example.com is having problem … and all the domain registration in the whois database shows ‘joe@example.com’, Joe won’t be able to be notified there is a problem.

The contact information is publicly accessible via the ‘whois’ databases.

Domain registrars that offer whois privacy capabilities should let you list more than one email address when they redirect the email address that they list in the whois look-ups.

For privacy sake, I like using a PO Box for the mailing address on all my domains.

AT&T Microcell and Routers

Our area has never gotten good cell phone coverage.  Doesn’t really mater what carrier we used … AT&T or Verizon.

When AT&T announced that it was going to be making “MicroCells” available, I decided to get one … as it would help our cell phone coverage.

The MicroCell has been working fine for more than a year … but, all of a sudden (or so it seemed), it stopped working correctly.

I contacted AT&T and they tried a few things and asked me to try cycling power (unplugging it and plugging it back in).  Nothing worked.  I asked them to check to see if it was still under warranty … it wasn’t.

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Creating Bootable Ghost Recovery USB Flash Drive

Those of you who follow my blog (or know me in person) are well aware that I’m a big fan of Norton Ghost backup software.

One of the major problems I’ve had with Norton Ghost is the fact that it only provides the ability to create a recovery CD … it doesn’t provide any ability to install the recovery software on a USB flash drive.   USB flash drives are much faster that CD’s and are read/write, so they can be updated at a later date.

After a bit of digging, I’ve figured out how to create one without too much trouble.

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Wake On LAN

There is apparently going to be a bit more getting used to this new laptop.

The other day, before I went to bed, I put my new Dell Latitude E6400 into standby mode … I’m 99% sure I did this.

The next morning, however, when I went down stairs I found my laptop powered on.

That evening, before I went to bed I hibernated the laptop.

Once again, the next morning, I found the laptop powered on.

Obviously this is pretty odd.

So last night I tried an experiment … I put the laptop into standby mode and, within seconds, it resumed from standby.   I then put the laptop into hibernate mode … and 30 minutes later, it powered itself back up.

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iPhone Buzzing

Ever since I got the iPhone, I’ve noticed that it causes nearby speakers (radios, desk phones, etc) to emit a buzzing noise.

The odd thing is, my boss Brian’s Blackberry does the same thing.

I finally found the reason why:

The cause of this buzzing has to do with GSM’s “time division nature. The ever-knowledgeable Keith Nowak, spokesperson for Nokia, explains it as follows: “[[With GSM]] the RF transmitter is turned on/off at a fast rate, and that ‘pulsing’ is often picked up by nearby devices that don’t have good RF shielding. In the case of GSM the pulse rate is 217 Hz, which can be easily heard.

That Crazy GSM Buzz

When I put my iPhone in the clock radio / iPhone dock that Ginny got me for the holidays, it does the same thing. Luckily the dock isn’t recognized as being 100% iPhone compatible, so the iPhone offers to shut off the radio (go into Airplane mode) whenever I dock it. This eliminates the buzzing (mostly) because the phone isn’t transmitting.

Clean up /tmp

Recently I noticed that there’s a lot of temporary files in the /tmp directory on my mail server … all the files have spamassassin in the file name. I figured that in some cases, SpamAssassin (or programs it calls) isn’t cleaning up properly.

I whipped up this script that will clean up any spamassassin files & directories that are older than a set number of minutes (60 in my case)…

#!/bin/sh

AGE=60

if [ "$1" == "--test" ]
then
        CMD="-exec echo"
        echo "$0: test mode"
else
        CMD="-exec"
fi

/usr/bin/find /tmp \
        -mmin +$AGE \
        -name spamassassin.ocr* \
        $CMD /bin/rm -f '{}' \;

/usr/bin/find /tmp \
        -maxdepth 1 \
        -mmin +$AGE \
        -type d \
        -name .spamassassin\* \
        $CMD /bin/rm -rf '{}' \;

If you run the script with a parameter of ‘–test’, it will just show the commands it would have executed.

I put the script in /etc/cron.hourly directory so it gets executed every hour.

Thunderbird message list out of sync

Sometimes I find that the message list in Thunderbird gets out of sync with the message bodies. When this happens, if I click on a message in the list, the message body that is brought up doesn’t match the subject.

I found a easy solution … just shut down Thunderbird, delete the corresponding .msf file from the accounts data directory, and start Thunderbird back up. Thunderbird will rebuild the .msf file and everything should be fine again.

To find accounts data directory, click on the “Server Settings” category of the effected account and look at the “Local directory” field.

[tags]thunderbird, mozilla, email[/tags]