[AusNOG] Google DNS Blocking/Unblocking

[Mark ZZZ Smith]

I have no insights into any sort of blocking/DoS protection Google might do, however if your customers queries are all coming from a single address because they're behind a NAT, then that could look like a DoS attack and trigger blocking. I'd expect different UDP source ports for the different DNS queries would prevent that, however I have heard of a web proxy a few years ago that was using the same UDP source ports for all DNS queries.


________________________________
From: Paul Julian <paul at oxygennetworks.com.au>
To: "ausnog at lists.ausnog.net" <ausnog at lists.ausnog.net> 
Sent: Monday, 19 January 2015, 18:25
Subject: [AusNOG] Google DNS Blocking/Unblocking



We have noticed recently that some customers are complaining about not being able to resolve DNS via Google’s DNS servers, upon further investigation we have found that we seem to be getting blocked by Google from pinging or resolving DNS queries to their public servers, does anybody know if there is some way we can check what the issue might be ?
 
I have searched the net looking for information about finding out if your address ranges is blocked by them or anything like that but can’t seem to find anything at all.
 
The only plausible thing I can think of is that one of our customers has had a Trojan or some problem and been hitting Google’s servers and they have blocked our range or something.
 
We don’t do any blocking like that within our network nor do our upstream providers so I know it’s nothing there which is causing the problem, a trace route stops responding well outside our network as well.
 
I would appreciate any suggestions on where I might look for some answers for this as I can’t find anything in Google’s pages anywhere nor anything via searches.
 
Thanks
Paul
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