No internet after upgrade to 17.10

I upgraded my laptop to new Ubuntu distribution 17.10 this afternoon/evening and since then I cannot connect to the internet.

I have tried both wired and wireless connections, but the icon in the status bar shows a question mark over the connection icon whichever method I've tried. I originally thought it was a wireless problem (it's a Realtek RTL8833EE card) so tried to connect via Ethernet to download the latest driver but find I can't connect with wire either.

I had a similar problem last week with 17.04 which I resolved somehow but I can't find exactly what I did.

Please can I have some suggestions as to what I should try to troubleshoot.

EDIT: I have tried the question (and the answer) here:

DNS not working after upgrade 17.04 to 17.10

both by adding a line

[main]
dns=dnsmasq

under /etc/NetworkManager/NetworkManager.conf, and by checking the resolvconf.service via

$ systemctl status resolvconf

which is NOT showing an error like

resolvconf[623]: /etc/resolvconf/update.d/libc: Warning: /etc/resolv.conf is not a symbolic link to /run/resolvconf/resolv.conf

I have confirmed that /etc/resolv.conf is a symbolic link to /run/resolvconf/resolv.conf

Found the answer I used in 17.04:

How to disable systemd-resolved in Ubuntu?

It was systemd-resolved causing the DNS resolution problem. Following the instructions there to disable the service (and direct NetworkManager to use a different resolution service) has brought everything back up again.