bad referral

[Camus Moire]

Hello, 

analyzing my logs brought forth some lines like this:
ns named[196]: bad referral (. !< 37.com) from [xxx.xxx.xxx.xxx].53
where xxx.xxx.xxx.xxx are a nameservers in the void.
This line came frequently with different strange nameservers.

Well, my setup is only for privat things and therefore i'm not
deep introduced in 'Zen - the art of nameserving') . 
Is there a resource that explain such behavior. 

thanks in advance

Camus Moire




PS: bind 8.2.3-REL