Re: DUND pre-pppd script

Raymond Ingles wrote:
> On Wed, May 28, 2008 at 11:04 PM,  <[email protected]> wrote:
>   
>> Hi,
>>
>> I need to determine my ppp IP address pair before I run pppd.
>>
>> The reason is that I have several network interfaces running at once on my
>> system so I need to choose an IP address in a subnet that is not already
>> taken.
>>     
>
>  There are three private network ranges:
> http://en.wikipedia.org/wiki/Private_network
>
>  Almost always, you can find a range that's not going to be used by
> any other NIC in the system. If my home network is on a 10.x subnet,
> for example, and I'm letting people dial up via modem to a 192.168.x
> range, I could use a 172.16.x address range for DUN.
>   
Thanks, I should have been more explicit in my original email.

My device has eth0, usb0, ppp0 and possibly wlan0.

eth0 can be static, link-local or dhcp.
wlan0 can be static, link-local or dhcp.
usb0 is chosen to be on a private network range at connection time that
doesn't conflict with any of the above.
ppp0 is chosen to be on a private network range at connection time that
doesn't conflict with any of the above.

So you see that I have to choose an unused subnet dynamically in order
to keep everything happy and working. The problem is that pppd doesn't
seem to allow for choosing the IP address via a script.

To choose the free subnet I've written a script in Python that searches
all three 3 private network spaces against the existing connections and
then outputs a suitable range in various formats like ifconfig, pppd,
dhcpd.conf.

I think that I can solve this problem by configuring dund to call a pppd
wrapper which calculates the correct, non-colliding, subnet and then
passed on the arguments to pppd.

Aras



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