fwd: Re: [registrars] Re: panix.com hijacked

Joe Maimon jmaimon at ttec.com
Mon Jan 17 19:34:19 UTC 2005



Steven M. Bellovin wrote:

>In message <Pine.LNX.4.44.0501161225210.11207-100000 at sokol.elan.net>, "william(
>at)elan.net" writes:
>  
>
>>On Sun, 16 Jan 2005, Joe Maimon wrote:
>>
>>    
>>
>>>Thus justifying those who load their NS and corresponding NS's A records 
>>>with nice long TTL
>>>      
>>>
>>Although this wasn't a problem in this case (hijacker did not appear to 
>>have been interested in controlling dns since it points to default domain
>>registration and under construction page), but long TTL trick could be 
>>used by hijackers - i.e. he gets some very popular domain, changes dns to 
>>the one he controls and purposely sets long TTL. Now even if registrars 
>>are able to act quickly and change registration back, those who cached new
>>dns data would keep it for quite long in their cache.
>>
>>    
>>
>
>Many versions of bind have a parameter that caps TTLs to some rational 
>maximum value -- by default in bind9, 3 hours.  Unfortunately, the 
>documentation suggests that the purpose of the max-ncache-ttl parameter 
>is to let you increase the cap, in order to improve performance and 
>decrease network traffic.  
>
>The suggestion that someone made the other day -- that the TTL on zones 
>be ramped up gradually by the registries after creation or transfer -- 
>is, I think, a good one.
>
>		--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb
>
>
>  
>
 From bv9ARM

*max-ncache-ttl*

    To reduce network traffic and increase performance the server stores
    negative answers. *max-ncache-ttl* is used to set a maximum
    retention time for these answers in the server in seconds. The
    default *max-ncache-ttl* is 10800 seconds (3 hours).
    *max-ncache-ttl* cannot exceed 7 days and will be silently truncated
    to 7 days if set to a greater value.

*max-cache-ttl*

    *max-cache-ttl* sets the maximum time for which the server will
    cache ordinary (positive) answers. The default is one week (7 days).


So loading TTL's to longer than 7 days will have diminishing returns.
Is this really such a good thing?

Joe



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