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My ISP had some network issues today, and these manifested as a very strange problem. For some reason, the only websites accessible were those belonging to the ISP and to Google. However, all sites that I tried were resolving using DNS (I tried using both my ISP's and Google's DNS servers in conjunction with nslookup), they just would not load or respond to pings.

Every Google-owned website that I tried to access worked flawlessly, including Youtube and Google+. I could even access Google sites hosted outside my geographic area (India), such as google.de and google.co.za. It wasn't due to Google being cached by my ISP as Google+ continued to update in real-time, and I very much doubt that my ISP is caching all of Youtube.

I couldn't access any other sites hosted within India, or even within my city, so it doesn't look like a severed cable was to blame. Traceroute showed requests leaving my ISP's network as well.

Does anyone know of a network issue that could cause such a problem? My normal suspect in cases like these would be the nameservers, but I eliminated those as a problem.

Chinmay Kanchi
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Sometimes (bigger) ISPs have direct connections with google datancenters, and have separate routing for it. So it is possible that google services are working, but "the rest" of the internet is not. Try running "traceroute" to see where you connections fail. If the connections to google go via different ISPs routers then other connections, his is a possibility.

Google international sites can be hosted there too (check the ip of google.de and google.co.za, and check the whois for it if you can, to see where it's hosted).

mulaz
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  • Requests to Google websites seem to make an extra hop inside my ISP's network, as opposed to others, so your explanation might be the answer. I'm going to wait a while for other answers before I accept yours, though. – Chinmay Kanchi Jun 27 '12 at 22:53
  • I agree. Your ISP likely has a peering connection to Google, which was up, and a transit connection for everything they don't peer with, which was down. – David Schwartz Jun 27 '12 at 23:00
  • Looks like you are right. A closer look at `traceroute` suggests that packets jump straight from my ISP's network in India to an IP address in Mountain View, CA that is owned by Google with no hops in between. Also, a look at pings shows that it takes essentially the same time for a ping to get to my ISP's servers and back as it does to Google's. It surprises me that there appears to be a private fibre optic line between India and CA, but there you go. – Chinmay Kanchi Jun 28 '12 at 03:57
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    That may be an illusion. The server is likely physically located in India, just on IP addresses assigned to a California company. – David Schwartz Jun 28 '12 at 04:46
  • Ah, that would indeed be more likely. I wasn't aware that IPs could be moved about willy-nilly, though I suppose, with the ISP and Google having sole control of their ends of the connection, the network topology is what they tell say it is. – Chinmay Kanchi Jun 28 '12 at 04:55