PFLOG(4) FreeBSD Kernel Interfaces Manual PFLOG(4)


pflogpacket filter logging interface


device pflog


The pflog interface is a 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


The pflog device first appeared in OpenBSD 3.0.
May 31, 2007 FreeBSD