NPF is a BSD licensed stateful packet filter, a central piece of software for firewalling. It is comparable to iptables, ipfw, ipfilter and PF. NPF is developed on NetBSD.

History

NPF was primarily written by Mindaugas Rasiukevicius. NPF first appeared in the NetBSD 6.0 release in 2012.

Features

NPF is designed for high performance on SMP systems and for easy extensibility. It supports various forms of Network Address Translation (NAT), stateful packet inspection, tree and hash tables for IP sets, bytecode (BPF or n-code) for custom filter rules and other features. NPF has extension framework for supporting custom modules. Features such as packet logging, traffic normalization, random blocking are provided as NPF extensions.

Example of npf.conf

$ext_if = inet4(wm0) $int_if = inet4(wm1) table <1> type hash file "/etc/npf_blacklist" table <2> type tree dynamic $services_tcp = { http, https, smtp, domain, 9022 } $services_udp = { domain, ntp } $localnet = { 10.1.1.0/24 } map $ext_if dynamic 10.1.1.0/24 -> $ext_if map $ext_if dynamic 10.1.1.2 port 22 <- $ext_if port 9022 procedure "log" { log: npflog0 } group "external" on $ext_if {

Stateful passing of all outgoing traffic.

pass stateful out final all block in final from <1> pass stateful in final family inet proto tcp to $ext_if port ssh apply "log" pass stateful in final proto tcp to $ext_if port $services_tcp pass stateful in final proto udp to $ext_if port $services_udp

Passive FTP and traceroute

pass stateful in final proto tcp to $ext_if port 49151-65535 pass stateful in final proto udp to $ext_if port 33434-33600 } group "internal" on $int_if {

Ingress filtering as per RFC 2827.

block in all pass in final from $localnet pass in final from <2> pass out final all } group default { pass final on lo0 all block all }