Comment 267 for bug 417757

Ok, you have a bug. But are you sure it is a bug in Ubuntu?
Do you have any other OS working correctly with the same router?

Please have a look at your network traffic. (Wireshark is nice for this.)

*This* bug goes like this:
Ubuntu: Hey router, what is IPv6 address of
Router: (ignores that question and does not answer at all)
Ubuntu: (waits for an answer for some seconds and finally...)
Ubuntu: Ok, I assume you don't have one. Then do you have any IPv4 address of
Router: (answering immediately) Sure, here you are.

With disabled IPv6 Ubuntu does only ask for a IPv4 address and the problem is no longer visible.
If your bug does not go away after disabling IPv6 it is *not* this bug.

Please investigate where your delay comes from. Is it really the router not answering at all? Does it really involve IPv6?
Is there really something Ubuntu can do to fix this? (i.e. are there other OS which do?)