Blogspot-Airtel Problem: Our Analysis

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There have been lot of news about Airtel blocking blogspot today.

Well, did they really blocked it?

It’s very hard to give a direct answer to that. Firstly, I believe that Airtel must have not intentionally blocked whole domain name (well they are a big ISP, and I don’t think they will go that kidish!).

What could be problem?
To understand that - let’s break Internet connection into parts as per TCP/IP model

1. Physical layer + Data Link layer on bottom most

2. Network layer - DNS, Internet routing, BGP stuff

3. Transport + Application layer - web browsers, scripting, web servers, data rendering etc

Well - Physical and data link layer were not really issues - since people who were having issues must be on a system “connected” to Internet, and same with Google’s Indian mirrors (which are usually on datacenter with redundant physical links)

Next, we see #2 Network layer - yes there can be issues here. And since people were not able to open website at all, rather then getting error 404, 500 or say a broken site - there was not really issue with Transport + Application layer.

So what can be possible issues at Network layer?

Broadly speaking - it consists of two parts - DNS and Internet routing.

DNS, as I explain is last post simple resolves into IP address. I have seen a few traceroutes on Internet - and they are all timing out after a certain IP address. From that it clearly seems issue was not on Airtel’s DNS servers. If it was issue at DNS servers - then would be getting - “Name not found” error in web browser, rather then “request timed out”.

This was surely issue which we can say under “Internet routing”. That is - when you get IP address of - next, you try to connect to that machine to create a “socket connection”.

In order to find the “Physical network location” of server, ISP’s core routers use protocol called BGP - Border Gateway Protocol. This helps in creating a “path” between your system and data packets flows above it.

Right now it seems like issue is resolved. Well here’s one traceroute from popular website - IBN Live

So, we see that things started timing out at 7th hop. Last hop which responded was node with IP address - Well, this IP address belongs to Autonomous System 9498 which is of Airtel. This means till hop 6th we were still on Airtel’s network.

Next, here’s one of traceroute taken at evening when was working fine.

If you observe, hop 5th here is same as hop 6th in last traceroute which was last node which responded -

In this working scenario - we see two hops are: &

First IP belongs again to Airtel, and next one is of ASN 15169 - belonging to Google. So clearly on 7th hop we are on Google’s network.With that all we can say is - there was certainly problem between either of two networks - Airtel or Google. The point from where they “peer” that is “interconnect” seems to be not available during daytime.

From traceroutes we can’t directly predict if it was just Airtel’s network or Google’s network or could be a router inside Google’s datacenter which links with Airtel’s domestic backbone. It can be glitch on BGP routers of Airtel or Google (in case of Google - the one which is specifically used in link with Airtel) as people on BSNL didn’t reported any such case.

If you are still having trouble in accessing - please do send us traceroutes and we would be more then happy to investigate further.

To do a traceroute on windows machine, just click on Start > run > (enter) cmd.exe
Next, in command prompt type - tracert and then send us the screenshot.

About the author:

Anurag is a Student and a part time network admin at dito.

He is all around network related technologies like DNS, Internet routing, servers, connectivity etc. He is also one of Power Posters at Official Google Apps forum and is involved in deployment of Google Apps.

Anurag is doing bachelors in Information & Technology from a State college in Haryana.

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