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Old 2nd October 2008
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Default Reliable method to get an IP?

OK I have a few pppoe connections... which can be viewed on the command line by `ifconfig pppoe0` `ifconfig pppoe1` and so on...

I was wondering what's the most reliable way to get the IP address of them?

They all have different dynamic IP and changes over time... I want a way to detect the changes...

I was thinking of writing a python script that parses the output of `ifconfig pppoeX` and grab the IP address, compare to the one if had before.

The python script would need to be run as a cron job... maybe every 10 minutes, or every hour.

Are there any better way to do this? in pf rules one can do something like (pppoe) which seems to be more "event driven", when the changes occur it notifies pf somehow...

If there are more effective way that is "event driven" like so that I don't need to run a cron job, I don't mind if it had to be written in C or something... as long as it exist...

Cheers.
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Old 2nd October 2008
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PF will automatically adjust rules if you place the interface within parentheses, and the IP address changes.

Tools for managing dynamic IP addresses are already in the ports/packages system. For example, I use net/ddclient to keep my DNS records up-to-date at dyndns.org.
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Yes I am using ddclient as of right now, as far as I can see it is using a web site to check its IP... this would work fine with one IP address, but it'll not work with multiple pppoe connections because there would be only one default gateway...

I notice that in the ddclient configuration that one can give it a nic name instead... I guess the question is that rather if it will work with BSD or if it assumes that it is on a Linux system and couldn't figure it out...
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Perhaps.

There are only two ways to check IP address assignments that I can think of:

1) Examining IP addresses in ifconfig output, as you have already suggested (there might be a sysctl too, but this is the same thing, really).
2) Connecting out and back, as ddclient does, because it is not operating system specific (as you have noted).

One could, I suppose, also check timestamps on /var/db/dhclient.leases.IFNAME; changing modification timestamps would show lease renewals or new address assignments. The content may also be examined for additional information, such as lease expirations.

Last edited by jggimi; 2nd October 2008 at 02:47 PM.
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Well, I have just look at closer look at ddclient.

It seems to be pretty flexible, I haven't tried this yet, but from the documentation on sourceforge, you can supply an interface name into it, which ddclient will in turn call ifconfig itself. It also seems like they have some smart regex text process build in that will parse the output of any ifconfig, rather on Linux or BSD, and search for something that looks like an IP address; additionally, you can specify a pattern which the search will only be perform after it.

A command can also be specified into ddclient, so you can write any script which can get the IP address from anywhere, and whatever it outputs ddclient will try to parse it and search for an IP... again it is the same as the specifying an interface name, one can supply a pattern which ddclient will skip in its search.

Got to try this out soon.
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Old 3rd October 2008
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You can use getifaddrs(3) if you want to do this programmatically.
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Ah, so getifaddrs(3) gets you a linked list of all interfaces on the system? Looks nice!
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Quote:
Originally Posted by Sunnz View Post
Ah, so getifaddrs(3) gets you a linked list of all interfaces on the system? Looks nice!
Yeah, see my blog entry here where I grab the MAC address, but the ip address shouldn't be much different.

http://othermark.livejournal.com/3005.html
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Wow that's very nice it should be a very trivial change to make it return with IP instead, thanks a lot!!
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