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.
