Secondary and TLD not updating

[Kevin Darcy]

Dan at spore.ath.cx wrote:
> Just because individual records are public doesn't mean you should allow just anyone to configure their nameserver as a slave to your domain.  
>
> There's no benefit to allowing transfers to just anybody except for the allowance it makes for the laziness of admins.
>   
Incorrect. I've often AXFR'ed people's zones to help troubleshoot 
problems they've reported.
> Weigh that against the  risks of DoS attacks, and the sucking up of previous upload bandwidth by domain transfers out.  Each such transfer could well use many many queries worth of bandwidth.
Individual queries of every record in the zone consumes as much or even 
more bandwidth.

Moreover, if a would-be hacker were to start *guessing* at names in the 
zone, then the total query traffic might actually be *substantially* 
larger than the zone transfer would be.

(If Intrusion Detection/Prevention is in place, the hacker could "fly 
under the radar horizon" by spreading the queries over a moderately-long 
period of time, from different clients in a botnet, but the aggregate 
traffic might still be higher than an AXFR).

Perhaps you don't understand that AXFRs are TCP. So reflection attacks 
aren't really an issue, and the usual concerns about 
DoS-amplification-via-reflector are misplaced.

Admittedly, if one has exceptionally large RRsets in a given zone (e.g. 
using TXT RRs as a kind of _ad_hoc_ database), then allowing AXFRs might 
enable the hackers to find those RRsets and use them for amplification 
in subsequent DoS attacks. But the moral of that story is that one 
shouldn't use DNS as a generic distributed database, not that open AXFRs 
are inherently a security vulnerability.

We never experienced any problems with having zone transfers completely 
open, for years. I realize that's just anecdotal evidence, but, on the 
other hand, are there any documented cases where open AXFRs were 
actually used in any kind of attack? If not, then I call FUD.
>  
>
> Its one more potential vulnerability with no particular benefit.  Sounds like a poor trade to me.   
>   
That's one opinion. I cited a "particular benefit" above. Another 
benefit is that maintaining lists of "authorized" slaves, potentially on 
a zone-by-zone basis, complicates named.conf and, as we all know, 
complicated configs lead to a higher risk of error, which can itself 
lead itself to security breaches.

- Kevin

> ------Original Message------
> From: Res
> Sender: bind-users-bounces at lists.isc.org
> To: Jefferson Ogata
> Cc: bind-users at lists.isc.org
> Subject: Re: Secondary and TLD not updating
> Sent: Nov 17, 2008 4:20 PM
>
> On Mon, 17 Nov 2008, Jefferson Ogata wrote:
>
>   
>> On 2008-11-17 14:25, Holger Honert wrote:
>>     
>>> Chris Thompson schrieb:
>>>       
>>>> On Nov 17 2008, Res wrote:
>>>>         
>>>>> Ack! allow-transfer should never be any
>>>>>           
>>>> What, never? Why not?
>>>>
>>>>         
>>> Security issue! You really want everyone to download your zone(s)?
>>>       
>> I couldn't care less. If the security of my systems were the least bit
>> dependent on keeping DNS records secret, I would kinda suck as an admin,
>> wouldn't I?
>>     
>
>
> does your employer know this is your attitude? he/she might take a 
> different stand :) I know you'd no longer be working for me, if that was 
> your take on how things should be.
>
>
>