Monitoring traffic with munin and shorewall

I have been using munin to monitor servers for some time. Recently I noticed a message in pages generated by network traffic plugin if_ which stated the plugin doesn't work reliably on 32 bit systems were bursts may exceed 50Mbps. As I was monitoring a 100Mbit and 1Gbit interface this problem could effect my system. The message from the if_ plugin suggested I use the ip_ plugin which uses iptables to find the packet count and should work on a 32 bit system. The problem with this plugin is that it requires you to add INPUT and OUTPUT tables