[Pdns-users] resolved it's a Cisco bug! (was query for an A record with content =

Bryan Fields Bryan at bryanfields.net
Sat Jul 13 00:05:40 UTC 2019

On 7/12/19 6:01 PM, Brian Candler wrote:
> On 12/07/2019 22:03, Bryan Fields wrote:
>> $ dig 50121.nodes.allstarlink.org @ if you want to see it fail.
> Works for me:

Well crap, must be a packet molester on my ISP, right?

> Are you sure you don't have some sort of DNS-inspecting firewall in 
> between your dig client and the server?
> Can you run tcpdump on the server itself, and see the query and/or response?

Server got query
Server sent response
IP of my ISP connection sends ICMP unreachable at the server (WTF??).

So I was investigating this a being some network messing around with my ISP.
Turns out it was my old cisco NAT router on my connection at home.  In classic
IOS it had a DNS ALG.  Using the below command it disabled it:

'no ip nat service alg udp dns'

And the problem was fixed.

I'm happy it's not my ISP, kinda pissed at myself it was my gear doing it.

Thanks to Brian and Ken for assisting on this!

PS. NAT is Evil.
Bryan Fields

727-409-1194 - Voice

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