Re: How to poll hostname from local name server with wildcard

Like2Learn <like2learn@xxxxxxx> wrote:
On Jan 4, 3:52 pm, Chris Davies <chris-use...@xxxxxxxxxxxx> wrote:
Do you have control over these "special devices" (or any application
software that runs on them)?

Yes I have fully control on the devices, since I will write the
firmware as well.

If so, you may be better off having these devices listen for an
application-specific "are you out there?" broadcast request and get them
to reply to that.

Zeroconf is definitely a solution. However, I am looking for something
even simplier, better existing already. I believe for each LAN, the
DNS server and the DHCP server are almost always available. The DNS
server, or the local name server, shall save the host names already.
Thus if I know the host name (which is determined by the device's S/
N), then I shall be able to retrieve the IP (or hardware address) out
of the DNS server. What do you think?

I've said what I think, which is to turn your proposed solution inside out
and have the devices contact the manager rather than the other way around.


Alternatively, have your cross-platform application registered in the
local DNS (a SRV record might be good for this) and have your "special
devices" register with the application directly. You can use any user
defined port if it's a internal application, but you should consider
registering the port with IANA [*] if it's for public/external use.


I think I am lost. The application will run at a PC (either Windows or
Linux), while the device firmware will run at a device, which is a
Linux box. They shall be registered separately, not together, right?

There are two options I can suggest:

1. Have your "cross-platform application" (a device management
application?) registered in the DNS with a well known service name. Then
the devices will be able to find it and tell it they exist. You could
do this using a zeroconf type approach or with a suitable SRV record in
the DNS.

2. Have your "cross-platform application" periodically shout "Who's out
there?" as either a broadcast (LAN) or multicast (WAN) request. The
devices would be listening for the question and would each answer
"I'm here". This requires no dependency on either DHCP or DNS and would
be my preferred approach.

In neither case would you need to worry about IP address allocation or
name resolution specifics, so a problematic part of your design simply
vanishes.


Like2Learn <like2learn@xxxxxxx> also wrote:
I believe for each LAN, the DNS server and the DHCP server are almost
always available.

If that's your underlying premise then you shouldn't need to worry about
checking those systems' availability. (Personally I think it's a false
assumption.)

The DNS server, or the local name server, shall save the host names
already. Thus if I know the host name (which is determined by the
device's S/N), then I shall be able to retrieve the IP (or hardware
address) out of the DNS server.

You're not going to win any praise from system administrators if you
force them to deploy your devices' naming scheme in their DNS.


For cases that I don't know the S/N of the device beforehand, I want to
know how many devices are now connected to the LAN, and pick up one for
connection. That is the main reason that I want to poll "SpecialDevice"
together with a wildcard. Any idea for this case?

Another poster has already said that you can't query a DNS with a
wildcard. (You can try a zone transfer and iterate across it, but that
presupposes the DNS server will let you have a zone, and many won't.)

Chris
.

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