View source for Linux iptables captive portal traffic shaping scripts (PortalShaper)

==Link monitoring==
The script <code>test-ppp</code> monitors each external interface by attempting to ping external servers through that interface. If an interface fails then it is automatically restarted.

The script is designed to work with a Solos PCI ADSL modem. Experience has shown that sometimes the whole module will fail, in which case it will need unloading and reloading. If all interfaces have failed then this is exactly what is done.

A check is done at the end of the script to re-run the <code>master</code> script if the number of available interfaces has changed. This will cause a count of the number of available interfaces to be performed, and the load balancing updated as required. The <code>default-gw</code> script will also be run to change the main default gateway if required.

The script is not perfect, because if the interface with the default gateway on fails, then the DNS lookup cannot be performed and it therefore looks like all interfaces have failed.

A better solution is possibly LSM (http://lsm.foobar.fi/) which I have not looked at yet.