This worked for me:
Find your hosts file here: C:\Windows\System32\Drivers\etc\hosts
Copy/paste the hosts file to your desktop.
Rename the file so it becomes “hosts.txt”
Now open the file with notepad. (you need to run as admin if you have that option)
Add this line at the bottom:
174.35.56.164 assetcdn.101.arenanetworks.com
Save the file.
Now rename the file again to delete the .txt so it has no file extension anymore and is just “hosts” again.
Now go replace your old hosts file with this new edited one on your desktop.
If you have the GW2 launcher already open, restart it.
This was someone else’s fix, but it worked for me when the Google DNS didn’t work right away.
I tried this with no luck, I also have FIOS.
This issue is ridiculous, I can’t believe how many people this is affecting without any sign of it getting fixed.