Sharing ppp connection with wlan interface

[edit] Requirements

The following programs must have been installed in order to share the ppp connection:

Programs for configuring your wlan card (package wireless_tools)
Programs for configuring generic network interface card (package net-tools)
The iptables program which is used to manipulate how data is passed through your machine from your clients and back (package iptables)
dnsmasq software for acting as a DHCP and DNS caching server (package dnsmasq)

The following conditions must also have been met:

You must have a working ppp connection (I'm using bluetooth+gprs to connect to the Internet)
You must have a working wlan interface card (in terms of "can be used in Linux")

Set the ppp connection up.
Set the wlan connection up. Choose ssid and select ad-hoc as network type. In the following I'm assuming that you are using interface named wlan0 . Set the wlan interface up address for example 192.168.0.254 . Setting up the interface is usually done by running the iwconfig program as root, with syntax like:
```
iwconfig wlan0 essid "My_Free_Wlan" mode Ad-Hoc
```
After that you can assign an ip address to the interface as usual, by running (again, as root):
```
ifconfig wlan0 192.168.0.254
```
Please note that different wlan cards may be configured differently and one should adapt this documentation accordingly.
Set the kernel to router mode. This is done by running as root:
```
echo 1 > /proc/sys/net/ipv4/ip_forward
```

Configure dnsmasqd. Make the following changes to /etc/dnsmasq.conf (uncomment if necessary):

domain-needed
bogus-priv
interface=wlan0 (or whatever interface your wlan is)
dhcp-range=192.168.0.1,192.168.0.100,12h

Start the dnsmasqd, as root:
```
/etc/rc.d/dnsmasq start
```
Finally, set firewall to forward connections to and from the Internet for clients connecting to your wlan. This is done by issuing (you guessed it right, as root again):
```
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
```
In the above the ppp0 interface is the used ppp interface, you can substitute it for yours if needed.
You are done! Happy surfing

WARNING The previous configuration has no security options enabled! If you are using firewall, you should adapt this documentation to suit your needs. Same applies also to setting up keys for wlan interface.