I was getting `Update information is outdated` alert. I tried `sudo apt-get update` and got these errors:

```
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/Release.gpg  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://repository.spotify.com/dists/stable/Release.gpg  Something wicked happened resolving 'repository.spotify.com:http' (-11 - System error)
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/main/i18n/Translation-en_IN  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/main/i18n/Translation-en  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/multiverse/i18n/Translation-en_IN  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/multiverse/i18n/Translation-en  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/restricted/i18n/Translation-en_IN  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/restricted/i18n/Translation-en  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/universe/i18n/Translation-en_IN  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/universe/i18n/Translation-en  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/universe/source/Sources  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/main/source/Sources  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/multiverse/source/Sources  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/restricted/source/Sources  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/main/binary-i386/Packages  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/restricted/binary-i386/Packages  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/universe/binary-i386/Packages  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/raring-security/multiverse/binary-i386/Packages  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1562::13). - connect (101: Network is unreachable) [IP: 2001:67c:1562::13 80]

E: Some index files failed to download. They have been ignored, or old ones used instead.

```

I followed [this](https://askubuntu.com/questions/111597/how-can-i-work-around-something-wicked-happened-resolving-mirror-errors) thread's top answer and it fixed the problem.

But someone please explain what was the problem and how did it got fixed?