[Pdns-users] Missing Answers RR in some response

[Vu Le]

Hi! We are testing pdns-recursor 3.6 with a query rate about 5000
query/s. The test is simple query for A record of a single domain. I
was surprised to found that about 10-20% of the reply don't have
Answer RR section. I have disabled the packet cache but the result is
the same.

Does someone have an idea how this may be happen? Is that the new DoS
protection feature of pdns-resursor?

Thanks,
Vu

-------------
Normal packet
-------------
Domain Name System (response)
    [Request In: 9]
    [Time: 0.000219000 seconds]
    Transaction ID: 0x002b
    Flags: 0x8080 (Standard query response, No error)
        1... .... .... .... = Response: Message is a response
        .000 0... .... .... = Opcode: Standard query (0)
        .... .0.. .... .... = Authoritative: Server is not an
authority for domain
        .... ..0. .... .... = Truncated: Message is not truncated
        .... ...0 .... .... = Recursion desired: Don't do query recursively
        .... .... 1... .... = Recursion available: Server can do
recursive queries
        .... .... .0.. .... = Z: reserved (0)
        .... .... ..0. .... = Answer authenticated: Answer/authority
portion was not authenticated by the server
        .... .... ...0 .... = Non-authenticated data: Unacceptable
        .... .... .... 0000 = Reply code: No error (0)
    Questions: 1
    Answer RRs: 1
    Authority RRs: 0
    Additional RRs: 0
    Queries
        www.spirentcom.com: type A, class IN
            Name: www.spirentcom.com
            Type: A (Host address)
            Class: IN (0x0001)
    Answers
        www.spirentcom.com: type A, class IN, addr 69.20.41.238

------------------------
Packet missing answer RR
------------------------

Domain Name System (response)
    [Request In: 7]
    [Time: 0.000390000 seconds]
    Transaction ID: 0x002b
    Flags: 0x8080 (Standard query response, No error)
        1... .... .... .... = Response: Message is a response
        .000 0... .... .... = Opcode: Standard query (0)
        .... .0.. .... .... = Authoritative: Server is not an
authority for domain
        .... ..0. .... .... = Truncated: Message is not truncated
        .... ...0 .... .... = Recursion desired: Don't do query recursively
        .... .... 1... .... = Recursion available: Server can do
recursive queries
        .... .... .0.. .... = Z: reserved (0)
        .... .... ..0. .... = Answer authenticated: Answer/authority
portion was not authenticated by the server
        .... .... ...0 .... = Non-authenticated data: Unacceptable
        .... .... .... 0000 = Reply code: No error (0)
    Questions: 1
    Answer RRs: 0
    Authority RRs: 0
    Additional RRs: 0
    Queries
        www.spirentcom.com: type A, class IN
            Name: www.spirentcom.com
            Type: A (Host address)
            Class: IN (0x0001)