Why is RFC1918 space in public DNS evil?

Fred Baker fred at cisco.com
Mon Sep 18 13:04:55 UTC 2006

> I know the common wisdom is that putting 192.168 addresses in a  
> public zonefile is right up there with kicking babies who have just  
> had their candy stolen, but I'm really struggling to come up with  
> anything more authoritative than "just because, now eat your  
> brussel sprouts".

I think the best answer to that is to turn it on its head.

As Joe points out, exposing interior information unnecessarily is a  
security risk - leaving a treasure map with "X marks the spot"  
invites pirates of all sorts. In this case, it is not only exposing  
interior information (the.host.you.want.to.attack.example.com)  
unnecessarily, but also in a way that doesn't actually help anyone  
else. The address of my telephone is But do a  
traceroute to that address (ar the address of my family computer,  
which is, and I about guarantee that you will come to a  
different computer, for the simple reason that you aren't in any of  
my private domains.

So putting those addresses in the public DNS actually *only* helps me  
if I am someone who is bombarding your prophylactic defenses with  
messages intended to reach your chewy innards. Anyone else has no  
actual use for the internal addresses.

I think the right question for your client is: "why exactly did you  
want to do that?"

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