It has been 3 days, and the ISP I am subscribed to is having a partial internet outage. It can load a few websites; StackExchange (which I am using now), Google, YouTube, and Reddit works. However, almost 90% of the internet is down for me.
Can anyone explain me how can that happen? Does that mean my ISP is blacklisted, or should I ask them about any thing? Whenever I inquire about it, they say it would be back to normal by night. It's been 3 days, but it hasn't been completely up.
I'm thinking of switching the connection to another provider, but I thought I might get some info about this problem and what can be the cause of it first.
FYI: My ISP is Syscon Infoway in Mumbai and it's still currently partially down.
63 Answers
It's not uncommon for an ISP to have multiple upstream connections, and partition traffic over the different connections based on any number of factors, such as the destination, time of day etc.
So it's possible that one of their links went down and they didn't fail the rest of the traffic over to another link (or can't).
The ISP should have a status page on their site identifying any current network issues, or you should contact their technical support.
The first thing that you'll want to do is to get some information on what is actually happening. The information you have given does not suggest a thorough investigation, nor does it suggest how you could confirm tht the problem actually is your ISP.
The first thing that you'll want to do is a traceroute test to some of the sites that you cannot visit. You're looking to see if you can resolve the hostname to an IP address, and then, whether your connection times out after any hop on the traceroute. If the traceroute stops at a certain point, then you would have an idea where the problem lies, wither inside of your home network, your ISP, at the ISP and their backbone providers, or perhaps somewhere between the ISP and the hosts' servers.
There are times when an ISP cannot connect to certain peers or their connection is poor, when many sites can appear to be unavailable. But these are typically very rare since that is what they primarily want to prevent. On the other hand, there are many problems that could exist with your computer or local network, like viruses, improper DNS settings, etc.
Unfortunately, fully troubleshooting this sort of issue is well beyond the scope of one article. In general, you should either contact a local network administrator you trust, or contact the ISP. If there is a problem, they should be able to find it, and if not, they may be willing to help you figure out your problem.
It could be a number of things. Many ISP's will have multiple connections, with different traffic going through different paths - in some cases, only traffic to certain destinations is handed off over some links - typically in peering arrangements.
Most often the handling of these connections is managed using the dynamic routing protocol called BGP. As the number of connections grows (this can be beyond the control of the ISP), it is possible that the router simply can't handle the amount of paths and starts behaving erratically - which can explain some outages (They may need a bigger router, there upstream may need a bigger router, there may be routing issues between multiple places)
Similarly, one of there links could be under a DoS attack making it unuseable, and they can't simply route everything down a different path as the path of the DoS will follow the new route.
Its also possible that some sites have blacklisted them because of traffic originating from their network, while not others.
No one other then them can definitively tell you whats going on - and they probably won't - but from what you have described it would seem that for whatever reason their main upstream provider is not working, and they are relying on peering connections for partial connectivity. (Google~=Youtube and is probably connecting via a peer, not sure about the others)
