Extremely slow connection after 17.04 update

I had the exact same issue (just like @Mark Roberts).

Here is the fix:

Note: the current /etc/resolv.conf file is actually a symlink to ../run/resolvconf/resolv.conf which appears to be the core issue since it is not maintained by systemd-resolved.

Thus if you do an ls -la you'll see:

~# ls -la /etc/resolv.conf
lrwxrwxrwx 1 root 29 Apr 14 11:36 /etc/resolv.conf -> ../run/resolvconf/resolv.conf

so... to get around this do the following:

sudo rm -f /etc/resolv.conf
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

After that I kicked systemd-resolved just to make sure:

sudo systemctl restart systemd-resolved

This appears to work great because:

systemd-resolved maintains the /run/systemd/resolve/resolv.conf file for compatibility with traditional Linux programs. This file may be symlinked from /etc/resolv.conf and is always kept up-to-date, containing information about all known DNS servers.

Which I quoted DIRECTLY from the bug report:(bug # 1624320) and I believe it is the culprit.

I found this discussion which blames systemd-resolv (something to do with DNS) and suggests the workaround of setting DNSSEC=off in resolved.conf

The exact same workaround has just been released to the Zesty repositories: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1682499

So long story short: Run Software Updater right now. Maybe that will solve the issue...