[Pdns-users] RE ignoring non-query opcode 6

Brian Candler b.candler at pobox.com
Wed Feb 7 08:59:23 UTC 2018

On 07/02/2018 08:41, bert hubert wrote:
> no one knows why the A-10 is
> sending queries with this opcode

A quick Google search found this: 

The *default* healthcheck is to send garbage UDP packets (p553):

"Layer 4 UDP – Every 5 seconds, the ACOS device sends a packet with a 
valid UDP header and a garbage payload to the UDP port. The port passes 
the health check if it either does not reply, or replies with any type 
of packet except an ICMP Error message. "

But if you configure it to use the DNS healthcheck, it should send a 
valid query (p558):

"ACOS device sends a lookup request for the specified domain name or 
server IP address. By default, recursion is allowed. ... Optionally, you 
can disable recursion."

This should clearly be opcode 0.

I think the OP should take a tcpdump of the healthcheck packets. If they 
have configured DNS healthchecking, with a domain name to query, then 
they can submit the tcpdump as evidence of a bug.  If they are relying 
on the default UDP healthchecking then it won't be a valid DNS packet in 
the first place.



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