NPFLOG(4) | Device Drivers Manual | NPFLOG(4)

# NAME

`npflog` —
packet filter logging interface

# SYNOPSIS

`pseudo-device npflog`

# DESCRIPTION

The `npflog` interface is a pseudo-device which makes visible all packets logged by the npf(7) packet filter. Logged packets can be monitored in real time by invoking tcpdump(8) on the `npflog` interface, or stored to disk using npfd(8).

The npflog0 interface is created automatically at boot if npf(7) is enabled; further instances can be created using ifconfig(8).

Each packet retrieved on this interface has a header associated that presently matches the format used by pf(4). This header documents the address family, interface name, rule number, reason, action, and direction of the packet that was logged. This structure looks like:

    struct npfloghdr {
    	uint8_t		length;
    	sa_family_t	af;
    	uint8_t		action;
    	uint8_t		reason;
    	char		ifname[IFNAMSIZ];
    	char		ruleset[NPFLOG_RULESET_NAME_SIZE];
    	uint32_t	rulenr;
    	uint32_t	subrulenr;
    	uint32_t	uid;
    	uint32_t	pid;
    	uint32_t	rule_uid;
    	uint32_t	rule_pid;
    	uint8_t		dir;
    	uint8_t		pad[3];
    };

# EXAMPLES

Monitor all packets logged on the default interface:

    # tcpdump -n -e -tttt -i npflog0

# SEE ALSO

inet(4), inet6(4), netintro(4), npf(7), ifconfig(8), npfd(8), tcpdump(8)

# HISTORY

The `npflog` device first appeared in NetBSD 6.0.

June 29, 2023 | NetBSD 10.1