TCP/IP networking strange problem



This is a weird one and I’m posting this mostly for my own reference so I can recall this when I run across it again. About 6-10 months ago a client of mine was having problems accessing web login pages like yahoo and ebay. I tested from various Windows machines on their network and verified and pulled my hair out for a bit before coming across a tip to check into the MTU setting for the firewall. The internet access is through a dsl modem which connects to a machine acting as a firewall and then to the rest of the network.

So, I set the MTU on both interfaces of the firewall to 1492 (the default was 1500) and everything magically started working. The explanation of this was, our service providers network can handle at a maximum 1492 bits in a packet. (mtu stands for Maximum Transmission Unit) Normally anything bigger is broken up into smaller packets to fit under this threshold. What was peculiar is that this came up out of the blue.

So, last week they have an incident that causes me to swap out the dsl modem with an identical model, same firmware. I duplicate the settings. (MTU on these is controlled by ISP we can’t alter the dsl modem/router mtu) Everything seems to work, but since then the same problem has been going on. So, I jog my memory and look. The firewall is still set to 1492. So, I try changing it to 1450, thinking lower would be better. I call and leave a message and look and I’ve actually set it to 1500 by a mistype. I change it to 1450 and receive a call back. Essentially, “things worked for a minute and then quit again.” So, while I was on the phone I had him test again and then switched back to 1500 and one last test. Things were working. My best guess is that the old DSL modem for some reason couldn’t handle breaking up the packets. I don’t know why the new one couldn’t handle smaller packets, that is weird.

If anyone has any suggestions as to why, I’ll leave this open for comments.

Related Posts

Blog Traffic Exchange Related Posts
  • ClamAV 0.94.1 to phone home The release candidate for version 0.94.1 of clam antivirus and they are eager for people to get out and test it. There is a new feature in this release called "malware statistics gathering" that will pass along observed malware information back to clamav.net - they hope to be posting statistics......
  • Strange Problem Made Simple | Verizon DSL Modem confusion I had a machine that I picked up to test internet connectivity. They were able to do email, but not visit web pages. My first thought was that internet explorer may have been a bit sideways, but when I got it to the workbench I figured I had solved the......
  • More details on php exploit from last week Ok. I have a bit of time that I can sit down and get a little more detailed on what specifically happened late last week that shut the site down for a couple days. At one point, I had updated the ezcontents script for the main site (averyjparker.com), but I......
Blog Traffic Exchange Related Websites
  • Choosing Which State's 529 Plan to Use   There are tons of articles discussing which State's 529 Plan to use, however, most seem to focus on expense ratios and fund choices.  While those variables are obviously important I believe there is another issue that is often ignored.  By living in a certain State and participating in that certain State's......
  • Picked Up Harvest Energy Trust I bought some Harvest Energy Trust (HTE) today. Not a lot only 50 shares worth. The market is pretty volatile and historically the month of August is bearish for stocks 72% of the time (or something like that), but the recent 226 point drop in the market created a really......
  • My Journey’s July 16th 2009 Update One of the main reasons I started this site was to keep myself accountable to anyone that was reading. Ironic part, is that when I started I probably had no one reading so it was an exercise in futility! Fiscal Update My last update was on May 29, 2009 and......
www.pdf24.org    Send article as PDF   

Similar Posts


See what happened this day in history from either BBC Wikipedia
Search:
Keywords:
Amazon Logo

Leave a Reply

You must be logged in to post a comment.


Switch to our mobile site