ipa(8) allows to make IP accounting (network accounting) based on FreeBSD
IPv4/v6 Firewall (including IPFW2), OpenBSD Packet Filter and IP Filter
accounting rules on FreeBSD, NetBSD and OpenBSD.

It supports limits for accounting rules and limits events as "limit is
reached", "reached limit is expired", etc.  It understands time intervals
like "end of day", "end of week", "end of month", etc.

ipastat(8) is a viewer for IP accounting database made by ipa(8).