"Cannot initiate the connection to in.archive.ubuntu.com:80" when trying to run "sudo apt-get update" behind proxy

I am very new to Ubuntu. I am behind a secure proxy too. when I try to run sudo apt-get update I get the following error.

blah@blah-hp-15-notebook-pc:~$ sudo apt-get update
Err http://security.ubuntu.com vivid-security InRelease
Err http://in.archive.ubuntu.com vivid InRelease
Err http://security.ubuntu.com vivid-security Release.gpg
Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
Err http://in.archive.ubuntu.com vivid-updates InRelease         
Err http://in.archive.ubuntu.com vivid-backports InRelease
Err http://in.archive.ubuntu.com vivid Release.gpg                  
Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
Err http://in.archive.ubuntu.com vivid-updates Release.gpg
Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80] 
Err http://in.archive.ubuntu.com vivid-backports Release.gpg
Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80] 
Reading package lists... Done
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid/InRelease
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid-updates/InRelease   
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid-backports/InRelease
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/vivid-security/InRelease
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/vivid-security/Release.gpg  Cannot initiate the connection to security.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid/Release.gpg  Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid-updates/Release.gpg  Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/vivid-backports/Release.gpg  Cannot initiate the connection to in.archive.ubuntu.com:80 (2001:67c:1360:8c01::18). - connect (101: Network is unreachable) [IP: 2001:67c:1360:8c01::18 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.

Does anyone know how to start fixing it?

Solution 1:

I also face the same problem. To overcome it, you need to change the server to the main server.

Just go to Software & Updates and change the server to the main server next to Download from.