So your DNS server functions! That is strange because of the error you get with YaST.
You could try
nslookup download.opensuse.org
but I admit that I do not realy understand what is going on here (like most problems that seem to switch themselves on and off at random 
).
BTW, when you post computer output as above, please do so between CODE tags. You get them by clicking on the # button in the toolbar above the post editor. We prefer the prompt, the command, the output and the next prompt in one sweep of the mouse copied/pasted between those CODE tags.