Our connection to the internet is handled by 2 Debian GNU/Linux servers(stable edition) communicating with heartbeat 0.4.9.0l-7.2 from Debian repository. In case of a failure at our main transparent proxy/internet gateway server, the backup server takes over the proxy's IP address, thus providing the port with a reliable connection to the internet.
Using a keepalive of 1 second and deadtime of 3 seconds, tests have shown that in case of a failure, the network connection can be offline for as little as half a second or for as long as 5 seconds, for the IP takeover change to finish.