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
  • Network Security guide for the home or small business network - Part 9 - Know your network Once more into the breech... Ok you've taken account of the software and services on your pc. The next thing we need to talk about is knowing your network. Do you have any wireless access points? Not sure? Print servers? How many pcs? Are any of them portables? Public access?......
  • 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......
  • Nero for Linux The news is that Nero has announced NeroLinux a version of their cd burning software that will run under the linux operating system. The software is available in either rpm or deb binary (for either debian based or red-hat based package managed systems.) I've noticed that Nero install under wine......
Blog Traffic Exchange Related Websites
  • Content Network Vs. Google AdWords Search Network There are two choices in benefitting from the use of Google AdWords. You are able to choose to post your ads on Google’s search results pages or the search network, or you are able to opt to have your ads posted on sites associated to your company or the content......
  • Sony Ericsson Open 2011 This week in tennis featured one major tournament for all players, the Sony Ericsson open. This is a premier event that lasts for more than one week, once again pitting the best players in the world up against each other. The men’s tournament featured big name players like Rafael Nadal,......
  • 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