After changing my Internet service provider I found a strange “bug”. While connected using Tele2 ADSL I was unable to download files bigger than 1 MB.
No, I’m not talking about peer-to-peer filters. I’m talking about downloading stuff from a website, or simply updating my antivirus.
After some checks, trying many websites, changing protocol (FTP, SCP), dumping a log of the packets using Ethereal, i found tons of wrong packets. I searched in Google and I found a blog about that problem (I’m sorry but I lost the link).
The same solution was also exposed in a Microsoft Knowledge base article (English, Italian) titled “How to Troubleshoot Black Hole Router Issues“: somewhere in the Tele2 network, a router is connected via a “smaller” connection, leading to a packet fragmentation not noticed using ICMP messages.
The “solution” is to set the MTU of my ADSL router to the biggest value not leading to fragmentation. Finding that value is a little tricky: using the ping tool to send packets of a specific size and enabling the do not fragment flag you can find the value thanks to the messages in the console. Then set that value (plus 28 ) in the router and everything works.
Why is the title Customer satisfaction? When I noticed this problem, I first contacted Tele2 customer service: 10 minutes about “Are you talking about p2p?“, “We can’t do this type of limitation” and, last but not least, “Your software is bugged“. After my answer “I can do everything using 56k connection, then what is bugged?” they put me “on hold”, and after 5 more minutes the line was lost. The customer service closed 10 minutes later, but i was unable to speak with them in that time.
I wasted hours searching for a solution using all my knowledge and tools. How can a “non computer scientist” solve that? ADSL in Italy is expensive and advertisements are targeted to families and people with little knowledge about software and networks.
Post scriptum: customer service is not included in the monthly bill, you pay it everytime you call it.
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