[Pdns-users] pdns-authoritative: Meaning of "Received question from socket which had no remote address, dropping (Transport endpoint is not connected)"

[Thomas Mieslinger]

Hi,

during an incident this week, where the resolvers of an access provider 
decided to send their dns queries with UDP message buffer size = 512, 
powerdns sent compliant answers with tc=1 because the the queried zone 
is DNSSEC signed. In turn the access providers resolver sent the queries 
again over tcp.

I have configured a max-tcp-connections = 300 and did not see any 
message: "Limit of simultaneous TCP connections reached - raise 
max-tcp-connections"

But I saw lots of

Received question from socket which had no remote address, dropping 
(Transport endpoint is not connected)

messages in the pdns log. Reading the tcpdumps I found about half of the 
queries over tcp unanswered.

So what does this "Transport endpoint is not connected" error mean? Did 
the resolver close the connection before pdns sent the answer?

Is max-tcp-connections = 300 to high? What are recommended values for a 
2x10core E5-2660v3 Box?

Thanks in advance

Thomas