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PFLOG(4) Device Drivers Manual PFLOG(4)

pflogpacket filter logging interface

pseudo-device pflog

The pflog interface is a pseudo-device which makes visible all packets logged by the packet filter, pf(4). Logged packets can easily be monitored in real time by invoking tcpdump(8) on the pflog interface, or stored to disk using pflogd(8).

The pflog0 interface is created automatically at boot if both pf(4) and pflogd(8) are enabled; further instances can be created using ifconfig(8).

Each packet retrieved on this interface has a header associated with it of length PFLOG_HDRLEN. This header documents the address family, interface name, rule number, reason, action, and direction of the packet that was logged. This structure, defined in <net/if_pflog.h> looks like

struct pfloghdr {
	u_int8_t	length;
	sa_family_t	af;
	u_int8_t	action;
	u_int8_t	reason;
	char		ifname[IFNAMSIZ];
	char		ruleset[PFLOG_RULESET_NAME_SIZE];
	u_int32_t	rulenr;
	u_int32_t	subrulenr;
	uid_t		uid;
	pid_t		pid;
	uid_t		rule_uid;
	pid_t		rule_pid;
	u_int8_t	dir;
	u_int8_t	rewritten;
	sa_family_t	naf;
	u_int8_t	pad[1];
	struct pf_addr	saddr;
	struct pf_addr	daddr;
	u_int16_t	sport;
	u_int16_t	dport;

Create a pflog interface and monitor all packets logged on it:

# ifconfig pflog1 up
# tcpdump -n -e -ttt -i pflog1

inet(4), inet6(4), netintro(4), pf(4), ifconfig(8), pflogd(8), tcpdump(8)

The pflog device first appeared in OpenBSD 3.0.

January 21, 2014 OpenBSD-5.9