Comment 79 for bug 574886

@up
Yeah, that's basically the solution which has been suggested here for, like, 2 years? The problem with the fact this solution works it is that it only proves that the issue is external, that it's your router's built-in DNS server's fault - it's flooded with so many requests coming all at once. Apt might possibly implement a fallback mechanism of some sort, like detecting such a situation and polling the servers in sequence, but, well, I guess it's of low priority.