Wednesday, February 15, 2012

ICSI Netalyzr comparison of SiADSL and Tiscali

I'm in the process of migrating from SiADSL to Tiscali for my home ADSL connection. I have been very happy with SiADSL but I need more bandwidth in upload for video conferences, i.e. Google+ Hangouts with extras. The increase from 7Mb/512kb to 20Mb/1Mb should make a significant difference.

I heard from Michele that Tiscali blocks some ports so I wanted to have a record of the differences between the two provider in case I had problems. Netalyzr to the rescue! It can run as a Java Applet or as a command line client for the more security conscious. It takes several minutes to run and tests everything I ever knew about and then some...

So, what changes between Tiscali and SiADSL?

Tiscali blocks some TCP and UDP ports which I consider a feature, not a problem, if you have Windows machines on the network:

  • Direct TCP access to remote RPC servers (port 135) is blocked. This is probably for security reasons, as this protocol is generally not designed for use outside the local network.
  • Direct UDP access to remote NetBIOS NS servers (port 137) is blocked.
  • Direct UDP access to remote IKE key exchange servers (port 500) is blocked.

I was surprised to notice this potential problem though after I moved to Tiscali:

I passed from PPPoE which uses a max MTU of 1492 to PPPoA which supports 1500 and I had forgotten to update the max MTU on my border router. I tried to leave the max MTU at 1492 but quickly had problems so I increased it to 1500 and it has been working like a charm since. I would have blamed my connectivity problems at Tiscali unless Netalyzr found the problem for me.

I'm also pleased to see that this warning I had on the SiADSL connection is gone with Tiscali:

Exactly the behavior I have seen over the last year(s). Uploads with Picasa killed internet access and video conferencing with many participants is "impossible" even with no other traffic.


  1. Some ports (UDP 500) you tell are blocked sound strange to me since I have set up a L2TP VPN server @home and I can connect perfectly.
    Nevertheless you can find the complete specification (and blocked ports) at the following link:

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