New In 4.5: pflow(4) And pflow State Option

pflow(4) pseudo-device exports Netflow v5 data (introduced in OpenBSD 4.5)

• a sensor, records data on flows: source/destination address, start/end time, # bytes

• each connection consists of two flows (one for each direction)

• pflow fetches data from the PF state table

Potentially very detailed data on your traffic

Initially only netflow version 5 (IPv4 only), from OpenBSD 5.1 onwards, versions 9 and 10 (aka IPFIX) are supported (with IPv6). Check what your collector side can handle