Duplicate Address Detection bug

[Patrik Lahti <plahti%qnx.com@localhost>]

Hi,

I have observed the following behavior in NetBSD5. When I first bring up 
an interface it will auto-configure a link-local address and perform 
Duplicate Address Detection (DAD) correctly for it. But after 
subsequently bringing it down and then up again, it does not perform DAD 
again for that address. Disconnecting the cable and re-connecting it 
again, has the same problem.

As I understand RFC 4862 a node should do DAD each time the interface is 
enabled (connected), not just the first time it is enabled. Otherwise, 
while being disabled (or disconnected), another node may come along and 
successfully do DAD for the same address and start using it, and when 
the original node's interface is re-enabled (or re-connected) there will 
be duplicate addresses in use. Exactly the situation DAD is created to 
avoid!

I would appreciate any insight into this.

I can file a bug report if that's appropriate. Please note that while 
I've used NetBSD and have hacked networking code based upon it, I am a 
little new to coding in NetBSD proper. I have been looking into how to 
fix it and have some idea, but would appreciate other ideas.

Cheers!
/P