Recently (now that I am forced to work from home) I tried to access (from PM) a couple of NASA sites (fits.gsfc.nasa.gov and heasarc.gsfc.nasa.gov) and got a "site unreachable" message. When I asked my colleagues whether they knew of some problems, I was told that: (a) everything works normally from the institute (which is on the academic GARR network); (b) it works normally from home using some providers; (c) it does not work for those using as provider TIM (the main Italian Telecom company).
In fact a search finds rumours like this https://community.tim.it/t5/MODEM-ROUTE ... m-p/173088 (in Italian) that TIM has been inserted in some blacklists and this is causing the problem. At DNS level.
In fact if I am on ssh at the institute a ping, tracepath, host or nslookup resolves the affected sites addresses perfectly. If I try the same from home I get "time out - no servers can be reached". It is clearly a DNS problem as using another DNS on the fly e.g. host -d fits.gsfc.nasa.gov 184.108.40.206 it works.
Now before embarking in changing the default DNS (TIM ones) either on the router, or on the laptop (which unfortunately is an Ubuntu one ... I say unfortunately because Ubuntu handles DNS in an odd unfamiliar way ... it is not enough to ediy /etc/resolv.conf as I was used on OpenSuse), I tried a simpler approach i.e. I inserted the IP addresses and host names of the two interesting sites in /etc/hosts statically.
Now this works at the base level (ping and tracepath resolve the address) but NOT within the browser (still times out) and even with the "host" command it appears that there is a double lookup. I mean ...
- if I do host xxxx on a normal site I get a reply from 127.0.0.53#53 (which is the Ubuntu way to forward to the provider real DNS
- if I do host xxxx on an arbitrary NASA site I get time out no servers can be reached
- if I do host xxxx on the sites added in /etc/host I get a first reply from 127.0.0.53#53 returning the value from /etc/host and then a time out no servers can be reached (is it checking twice ? doing also a reverse ?)