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PFLOG(4) Device Drivers Manual PFLOG(4)


pflogpacket filter logging interface


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(1) 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[PF_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	pad[3]; 


Create a pflog interface and monitor all packets logged on it:
# ifconfig pflog1 up 
# tcpdump -n -e -ttt -i pflog1


tcpdump(1) inet(4), inet6(4), netintro(4), pf(4), ifconfig(8), pflogd(8)


The pflog device first appeared in OpenBSD 3.0.
December 10, 2001 Debian