The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

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Wednesday, February 18, 2015

A limitation sure, but it sneaks around its own limitations

I was reminded by Yesterday's post on DNS that I was playing around with SRV records, and oh yes, here's a few I set up some time ago:

_http._tcp              IN      SRV     1  1 8888 lucy
                        IN      SRV     2 10 8888 marvin
                        IN      SRV     2 20 8888 bunny-desktop
                        IN      SRV     2 30 8888 saltmine

So, let's see what I get when I query _http._tcp.roswell.area51. (the “home domain” I use around here):

  rcode = 0.000000,
  ra = true,
  aa = true,
  query = false,
  ad = false,
  rd = true,
  cd = false,
  tc = false,
  id = 1234.000000,

  question =
  {
    class = "IN",
    name = "_http._tcp.roswell.area51.",
    type = "SRV",
  },

Okay, so far, this is expected—some DNS flags, and the “question” we asked. Continuing …

  answers =
  {
    [1] =
    {
      port = 8888.000000,
      type = "SRV",
      name = "_http._tcp.roswell.area51.",
      weight = 30.000000,
      target = "saltmine.roswell.area51.",
      class = "IN",
      ttl = 86400.000000,
      priority = 2.000000,
    },
    [2] =
    {
      port = 8888.000000,
      type = "SRV",
      name = "_http._tcp.roswell.area51.",
      weight = 1.000000,
      target = "lucy.roswell.area51.",
      class = "IN",
      ttl = 86400.000000,
      priority = 1.000000,
    },
    [3] =
    {
      port = 8888.000000,
      type = "SRV",
      name = "_http._tcp.roswell.area51.",
      weight = 10.000000,
      target = "marvin.roswell.area51.",
      class = "IN",
      ttl = 86400.000000,
      priority = 2.000000,
    },
    [4] =
    {
      port = 8888.000000,
      type = "SRV",
      name = "_http._tcp.roswell.area51.",
      weight = 20.000000,
      target = "bunny-desktop.roswell.area51.",
      class = "IN",
      ttl = 86400.000000,
      priority = 2.000000,
    },
  },

Okay, these are the answers we were looking for, but wait? What's this?

  additional =
  {
    [1] =
    {
      type = "A",
      name = "lucy.roswell.area51.",
      address = "192.168.1.10",
      class = "IN",
      ttl = 86400.000000,
    },
    [2] =
    {
      type = "AAAA",
      name = "lucy.roswell.area51.",
      address = "fc00::1",
      class = "IN",
      ttl = 86400.000000,
    },
    [3] =
    {
      type = "A",
      name = "marvin.roswell.area51.",
      address = "192.168.1.13",
      class = "IN",
      ttl = 86400.000000,
    },
    [4] =
    {
      type = "AAAA",
      name = "marvin.roswell.area51.",
      address = "fc00::3",
      class = "IN",
      ttl = 86400.000000,
    },
    [5] =
    {
      type = "A",
      name = "bunny-desktop.roswell.area51.",
      address = "192.168.1.16",
      class = "IN",
      ttl = 86400.000000,
    },
    [6] =
    {
      type = "AAAA",
      name = "bunny-desktop.roswell.area51.",
      address = "fc00::2",
      class = "IN",
      ttl = 86400.000000,
    },
    [7] =
    {
      type = "A",
      name = "saltmine.roswell.area51.",
      address = "192.168.1.18",
      class = "IN",
      ttl = 86400.000000,
    },
    [8] =
    {
      type = "AAAA",
      name = "saltmine.roswell.area51.",
      address = "fc00::4",
      class = "IN",
      ttl = 86400.000000,
    },
  },

Yes, even though I run that braindead DNS implementation that only accepts single questions, it also preemptively sent back the appropriate IP addresses!

Will wonders never cease. There's probably no need for multiple DNS queries to handle SRV lookups.

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