[Bluez-users] DUND pre-pppd script

[Bluez-users] DUND pre-pppd script

[arasv]

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.

Would you recommend that I add a pre-ppp-up mechanism to dund to do this?

If someone knows how to get pppd to run a script *before* it reads its
configuration file then I would rather do that instead.

Aras


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Re: [Bluez-users] DUND pre-pppd script

[Raymond Ingles]

On Wed, May 28, 2008 at 11:04 PM,  <arasv@magtech.com.au> 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.

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Re: [Bluez-users] DUND pre-pppd script

[Brad Midgley]

Aras

> I need to determine my ppp IP address pair before I run pppd.

I ran into this when setting up a bluetooth AP for use with a couple
of nokia devices. They are using dun not pan, and I wanted to assign
different addresses to each device. I had to hardcode the ip addresses
in the nokias' dialup config which wasn't very satisfying.

-- 
Brad

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Re: [Bluez-users] DUND pre-pppd script

[Aras Vaichas]

Raymond Ingles wrote:
> On Wed, May 28, 2008 at 11:04 PM,  <arasv@magtech.com.au> 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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Re: [Bluez-users] DUND pre-pppd script

[Brad Midgley]

Aras

> 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.

although there is no way to coax dund to pass the remote btaddr
address on to a wrapper script, we should be able to figure it out.

tell dund to use the wrapper:
dund --pppd=mypppd ...

in the mypppd wrapper:
#!/bin/sh
BTADDR=`rfcomm show $2 | cut -d ' ' -f2`
# set LOCAL, REMOTE based on the BTADDR
pppd LOCAL:REMOTE $*

if dund were changed then the tty might no longer be on $2.
in my scenario at least, LOCAL would always be 0.0.0.0 and something
like /etc/ppp/ip-up.d/bridge would bridge pppX:

#!/bin/sh
# $2 is the ppp interface name
brctl addif pan0 $2

should be fun to see if any of this works :)

-- 
Brad

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Re: [Bluez-users] DUND pre-pppd script

[Brad Midgley]

fwiw,

this does work with some mods since linux won't bridge ppp. you still
have to ipmasq the 192.168.42.0 subnet in this example... but the
mypppd script can be simplified to a sort of poor man's dhcp server.
(trim the leases if you ever really connect 255 devices over the
lifetime of the server :)

#!/bin/sh
LEASES=/var/run/mypppd.leases
grep -q $DUN_BDADDR $LEASES || echo $DUN_BDADDR >>$LEASES
LOCAL=192.168.32.10
REMOTE=192.168.42.`grep -n $DUN_BDADDR $LEASES | cut -d : -f1`
pppd $LOCAL:$REMOTE $*

-- 
Brad

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Re: [Bluez-users] DUND pre-pppd script

[Aras Vaichas]

Brad Midgley wrote:
> Aras
>
>   
>> I need to determine my ppp IP address pair before I run pppd.
>>     
>
> I ran into this when setting up a bluetooth AP for use with a couple
> of nokia devices. They are using dun not pan, and I wanted to assign
> different addresses to each device. I had to hardcode the ip addresses
> in the nokias' dialup config which wasn't very satisfying.
>
>   

Thanks for the replies and ideas. What I've done is this:

#!/bin/sh
IP_PAIR=`safeip -p`
pppd $1 $2 ${IP_PAIR} $3 $4 $5 $6 $7 $8 $9


safeip is a Python script I wrote which finds a private subnet of size 2
that is not in use anywhere on the system. Option -p returns the data
like so: IP1:IP2

I just pass this IP pair on to pppd as well as all the other information
that dund passes on from itself and the /etc/default/bluetooth file.

Works quite well regardless of the state of (almost) any other possible
network configuration. I can also connect from multiple devices and it
just dishes out a new IP pair every time.

my /etc/default/bluetooth file has:
DUND_OPTIONS="--listen --persist --channel 3 --msdun --pppd pppd_pre.sh
crtscts 115200 ms-dns 10.0.0.1

I haven't fixed the ms-dns entry yet, but that is easily done

Aras

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