* * * * *
                                        
          A limitation sure, but it sneaks around its own limitations
                                        
I was reminded by Yesterday's post on DNS (Domain Name Service) [1] that I
was playing around with SRV (Service) 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 [2], it also preemptively sent back the appropriate IP
(Internet Protocol) addresses!

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

[1] gopher://gopher.conman.org/0Phlog:2015/02/17.1
[2] https://www.isc.org/downloads/bind/

Email Sean Conner at sean@conman.org

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