Comcast residential DNS contact

Jared Mauch jared at puck.nether.net
Wed Dec 3 15:28:29 UTC 2014


So have A record queries. Do you filter those as well?

Jared Mauch

> On Dec 3, 2014, at 9:08 AM, Stephen Satchell <list at satchell.net> wrote:
> 
>> On 12/03/2014 04:04 AM, Niels Bakker wrote:
>> * shortdudey123 at gmail.com (Grant Ridder) [Wed 03 Dec 2014, 12:54 CET]:
>>> Both of Google’s public DNS servers return complete results every time
>>> and one of the two comcast ones works fine.
>>> 
>>> If this is working by design, can you provide the RFC with that info?
>> 
>> An ANY query will typically return only what's already in the cache.  So
>> if you ask for MX records first and then query the same caching resolver
>> for ANY it won't return, say, any TXT records that may be present at the
>> authoritative nameserver.
>> 
>> This could be implementation dependent, but Comcast's isn't wrong, and
>> you should not rely on ANY queries returning full data.  This has been
>> hashed out to tears in the past, for example when qm**l used to do these
>> queries in an attempt to optimise DNS query volumes and RTT.
> 
> At the ISP I consult to, I filter all ANY queries, because they have
> been used for DNS amplification attacks.



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