Switching to TCP in BIND.

sthaug at nethelp.no sthaug at nethelp.no
Wed May 5 09:10:16 UTC 2010

> > > I know of no such feature. What do you mean by "spoofed" anyway? How
> > > would you expect named to detect "spoofing", and is that its job?
> > 
> > It seems (not tested by me) that Nominum CNS does that: when many
> > responses arrive which do not match (src IP address, query ID, etc)
> > any pending answer, it switches to TCP, assuming someone tries to
> > poison it.
> >  
> > This is supposed to be a protection against the Kaminsky attack.
> Interesting.  "Switches" by what means?  Returns TC responses to all UDP 
> queries?  Just for particular clients or particular domains?  Is this 
> documented at all (yes, I'm too lazy to Google :-) ).

According to the Nominum CNS manual,

"When a single query ID mismatch is detected in the expected DNS
response, CNS switches the recursive query to the more reliable TCP
protocol ..."

So it is definitely documented - though I'm sure there are details of
the implementation which are *not* documented in the regular user

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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