Error 101: Network is unreachable when trying to update

Have you tried changing the repository to the 'Main server'?

You can change it by opening 'Software & Updates' and selecting a different mirror.

From time to time the local repository mirrors go down so its always a good idea to check other ones ;)

I have also noticed that it is trying to connect via IPv6 which your router or ISP may not support. Have you tried this?