npfd(8) - NetBSD Manual Pages

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NPFD(8)                 NetBSD System Manager's Manual                 NPFD(8)


NAME

     npfd -- packet filter logging and state synchronization daemon


SYNOPSIS

     npfd [-D] [-d delay] [-f filename] [-i interface] [-p pidfile]
          [-s snaplen] [expression]


DESCRIPTION

     npfd is a background daemon which writes to a file in pcap(3) format
     logged packets read from an npflog interface.  The npflog interface is
     used by npf(7) to log packets as defined in npf.conf(5).  The generated
     pcap(3) files can then be analysed using tools such as tcpdump(8).

     npfd closes and then re-opens the log file when it receives SIGHUP, per-
     mitting newsyslog(8) to rotate logfiles automatically.  SIGALRM causes
     npfd to flush the current logfile buffers to the disk, thus making the
     most recent logs available.  The buffers are also flushed every delay
     seconds.

     If the log file contains data after a restart or a SIGHUP, new logs are
     appended to the existing file.  If the existing log file was created with
     a different snaplen, npfd temporarily uses the old snaplen to keep the
     log file consistent.

     npfd tries to preserve the integrity of the log file against I/O errors.
     Furthermore, integrity of an existing log file is verified before append-
     ing.  If there is an invalid log file or an I/O error, the log file is
     moved out of the way and a new one is created.  If a new file cannot be
     created, logging is suspended until a SIGHUP or a SIGALRM is received.

     If SIGINFO is received, then npfd logs capture statistics to syslogd(8).

     The options are as follows:

     -D      Debugging mode.  npfd does not disassociate from the controlling
             terminal.

     -d delay
             Time in seconds to delay between automatic flushes of the file.
             This may be specified with a value between 5 and 3600 seconds.
             If not specified, the default is 60 seconds.

     -f filename
             Log output filename.  Default is /var/log/npflog0.pcap.

     -i interface
             Specifies the npflog interface to use.  By default, npfd will use
             npflog0.

     -p pidfile
             Writes a file containing the process ID of the program.  The file
             name has the form /var/run/npfd.pid.  If the option is not given,
             pidfile defaults to npfd.

     -s snaplen
             Analyze at most the first snaplen bytes of data from each packet
             rather than the default of 116.  The default of 116 is adequate
             for IP, ICMP, TCP, and UDP headers but may truncate protocol
             information for other protocols.  Other file parsers may desire a
             higher snaplen.

     expression
             Selects which packets will be dumped, using the regular language
             of tcpdump(8).


FILES

     /var/run/npfd.pid      Process ID of the currently running npfd.
     /var/log/npflog0.pcap  Default log file.


EXAMPLES

     Log specific tcp packets to a different log file with a large snaplen
     (useful with a log-all rule to dump complete sessions):

           # npfd -s 1600 -f suspicious.log port 80 and host evilhost

     Log from another npflog interface, excluding specific packets:

           # npfd -i npflog3 -f network3.log "not (tcp and port 23)"

     Display binary logs:

           # tcpdump -n -e -ttt -r /var/log/npflog0.pcap

     Display the logs in real time (this does not interfere with the operation
     of npfd):

           # tcpdump -n -e -ttt -i npflog0

     Tcpdump has been extended to be able to filter on the OpenBSD pfloghdr
     structure defined in sys/net/npf/if_npflog.h.  Tcpdump can restrict the
     output to packets logged on a specified interface, a rule number, a rea-
     son, a direction, an IP family or an action.

     ip              Address family equals IPv4.
     ip6             Address family equals IPv6.
     ifname kue0     Interface name equals "kue0".
     on kue0         Interface name equals "kue0".
     ruleset rules   Ruleset name equals "rules".
     rulenum 10      Rule number equals 10.
     reason match    Reason equals match.
     action pass     Action equals pass.  Also accepts "block".
     inbound         The direction was inbound.
     outbound        The direction was outbound.

     Display the logs in real time of inbound packets that were blocked on the
     wi0 interface:

           # tcpdump -n -e -ttt -i npflog0 inbound and action block and on wi0

     Each npf(7) rule is marked with an id number, shown using:

           # npfctl show
           ...
                   block final all apply "log" # id="45"
           ...

     This id is the rule id shown by tcpdump:

           # tcpdump -enr /var/log/npflog0.pcap
           ...
           11:26:02.288199 rule 45.rules.0/0(match): block in on sk0: \
           1.2.3.4.46063 > 5.6.7.8.23231: Flags [S], seq 1, win 8192, \
           options [mss 1440], length 0
           ...


SEE ALSO

     pcap(3), npf.conf(5), npf(7), newsyslog(8), npfctl(8), tcpdump(8)


HISTORY

     The npfd command appeared in NetBSD 8.0.


AUTHORS

     This manual page was written by Can Erkin Acar <canacar@openbsd.org>.


CAVEATS

     Offline analysis of captured data is advised to alleviate issues with
     malicious data intended to exploit bugs in the packet parsing code of
     tcpdump(8).

NetBSD 10.0                     August 7, 2018                     NetBSD 10.0