traffic accounting software

[Jorge Salamero Sanz <bencer@cauterized.net>]

hi all,

which software would you recommend for traffic accouting on a firewall ?

i want monitor forwarded traffic and connections and graph it with
something like rrdtols.

i'd like to find something lightweight (ntop or nagios are too heavy) and
easyly customizable, alerts are a plus.

thanks :)