I have written a very simple (IPv4/IPv6 addresses only) DNS server which can use Lua to determine the IPs to return to the user (It was my big “do cool open source during the pandemic” project). To implement this particular problem, I whipped up this Lua script:

  -- This script is to be run by coLunacyDNS
  -- This script takes a query like 10.1.2.3.ip4.invalid. and returns the
  -- corresponding IP (e.g. 10.1.2.3 here)

  -- Change these IPs to the actual IPs the DNS server will run on
  bindIp = "127.0.0.1" -- We bind the server to the IP 127.0.0.1
  bindIp6 = "::1" -- Localhost for IPv6

  function processQuery(Q) -- Called for every DNS query received
    if Q.coQtype == 1 then
      local query = Q.coQuery
      if query:match("^%d+%.%d+%.%d+%.%d+%.ip4%.invalid%.$") then
        local ip = query:gsub("%.ip4%.invalid%.$","")
        return {co1Type = "A", co1Data = ip}
      end
    else
      return {co1Type = "notThere"}
    end
    return {co1Type = "notThere"}
  end

One will need coLunacyDNS to run this script:

  git clone https://github.com/samboy/MaraDNS
  cd MaraDNS/deadwood-github/tools/coLunacyDNS
  make
  sudo cp coLunacyDNS /usr/local/bin

Full documentation for coLunacyDNS is available:

https://github.com/samboy/MaraDNS/blob/master/deadwood-githu...