I’m on at least 2 blocklists at this point for the crime of not having reverse DNS set up. I don’t know how rDNS works. No amount of reading Wikipedia is helping me understand what I have to do.

  • I have a domain at a registrar which gives me bog standard DNS.
  • I have Apache running on my network.
  • I have PiHole running on my network.

My understanding is that rDNS is not set up at my registrar, but somewhere in my network. What do I do?

Thank you for your time.

  • chiisanaAEnglish
    2•11 months ago

    See this page here that explains the Flags: https://opensource.com/article/18/10/introduction-tcpdump

    Typically, in a TCP connection, you’d SYN, SYN+ACK, ACK, then transfer actual data over. In the successful sequence, you see this happening as expected.

    In the unsuccessful sequence, it seems to be stuck in SYN, SYN+ACK, but there is no ACK that follows (Flags [.]).

    Where is the second one captured? On the user’s system, or on your system? Something in between is determining the packet isn’t intended for the destination and dropping it. It may be a firewall, it may be something else.