Today, I’ve found some strange behaviour on my TDSL Business connection. Some DNS queries are being dropped at the routers of Deutsche Telekom and I wonder if this is a malfunction with their Internet filters. When I query random name servers using “dig www.google.com any”, those packets never reach their destination. I’ve asked for confirmation on IRC and it looks like others perceive the same odd behaviour.
I’ve investigated this a little bit and found that it is only port 53/udp that is being affected; doing dns queries over port 53/tcp is working fine. Thus, it looks like they are using some deep packet inspection at their routers as only special dns queries are being dropped. Can someone else confirm this odd behaviour?
