Re: local IP adresses / local host names

Subject: Re: local IP adresses / local host names
From: Andreas Fink <email@hidden>
Date: Thu, 10 Jul 2008 11:30:10 +0000

On 10.07.2008, at 11:12, Quinn wrote:

At 10:24 +0000 10/7/08, Andreas Fink wrote:
What is the correct way to get a list of local IP adresses and local host names?

For IP addresses, TN1145 demonstrates a number of techniques.

<http://developer.apple.com/technotes/tn/tn1145.html>

For DNS names, the problem is not solvable even in theory: I can happily add an name in my personal domain ("anarchistturtle.com") that points to someone else's host, and there's no way that host can discover its new name.

One reasonable heuristic is to reverse DNS each of the IPs (using <x-man-page://3/getaddrinfo>, CFHost, or whatever), but that might not give you the answer you're expecting. For example, my personal web server is "anarchistturtle.com" but if you reverse map its IP address you get "host217-41-101-22.in-addr.btopenworld.com".

If you can explain what you're using this information for, I can offer up some better heuristics.

I've looked at that information and its not useable in my case. Open Transport is definitively out of the picture. BSD Sockets are useable and in fact I use some similar code today to find out on incoming connection who connected to me and on which local ip. However I need this information at the time I set up connections.

Example: I'm connected to a corporate network via Ethernet and a WWAN network. I can bind to the WWAN IP or to the corporate IP or to "any". And same goes for IPv4 versus IPv6 sockets. To be able to decide on which IP's I want to listen to and to which I don't, I need to know what IP's are available on the system at the current time. So basically a list of IP Interfaces, their IP Addresses (IPv4 and IPv6) as they can have multiple. The host name is secondary and only used for display purposes. Reverse DNS or gethostname() should be sufficient in this case.

Andreas Fink

Fink Consulting GmbH

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	>Re: local IP adresses / local host names (From: Quinn <email@hidden>)

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