a *fast* check for whether another machine is on the local network?

Dar Scott dsc at swcp.com
Thu Jun 13 20:07:55 EDT 2013

Would a timeout you control be satisfactory?  

I was picturing LAN rather than VPN, so I was imagining a 50 ms timeout, but maybe you will need a second.  

The timeout spec for Windows ping has ms resolution.  The timeout for OS X ping has a second resolution.  You can try the arp test first.  

You can try opening a socket to a known service.  Or, if the computer is not stealth, even to a port that has no service listening on it.  There are a few gotchas, but that can work.  You have to do your own timeout.  


On Jun 13, 2013, at 5:19 PM, Dr. Hawkins wrote:

> On Thu, Jun 13, 2013 at 3:11 PM, Daryl Williams
> <daryl at synergetic-data.com> wrote:
>> It sounds like what you are really looking for is a local gateway to get to
>> the Internet, and to where ever the time entries are made?
> No; actually the opposite.
> If I have a connection, presumably by vpn (this is for postgres), I
> want to use it.  If there is no connection to the server, I want to
> put things into a local sqlite database, and use that to update the
> postgres base later.  I'm looking for a quick way to achieve this,
> rather than something with a lengthy timeout
> -- 
> Dr. Richard E. Hawkins, Esq.
> (702) 508-8462
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