iptables/xtables-monitor.8.in

.TH XTABLES\-MONITOR 8 "" "@PACKAGE_STRING@" "@PACKAGE_STRING@"
.SH NAME
xtables-monitor \(em show changes to rule set and trace-events
.SH SYNOPSIS
\fBxtables\-monitor\fP [\fB\-t\fP] [\fB\-e\fP] [\fB\-4\fP|\fB|\-6\fB]
.PP
\
.SH DESCRIPTION
.PP
.B xtables-monitor
is used to monitor changes to the ruleset or to show rule evaluation events
for packets tagged using the TRACE target.
.B xtables-monitor
will run until the user aborts execution, typically by using CTRL-C.
.RE
.SH OPTIONS
\fB\-e\fP, \fB\-\-event\fP
.TP
Watch for updates to the rule set.
Updates include creation of new tables, chains and rules and
the name of the program that caused the rule update.
.TP
\fB\-t\fP, \fB\-\-trace\fP
Watch for trace events generated by packets that have been tagged
using the TRACE target.
.TP
\fB\-4\fP
Restrict output to IPv4.
.TP
\fB\-6\fP
Restrict output to IPv6.
.SH EXAMPLE OUTPUT
.TP
.B xtables-monitor \-\-trace

 1 TRACE: 2 fc475095 raw:PREROUTING:rule:0x3:CONTINUE \-4 \-t raw \-A PREROUTING \-p icmp \-j TRACE
 2 PACKET: 0 fc475095 IN=lo LL=0x304 0000000000000000000000000800 SRC=127.0.0.1 DST=127.0.0.1 LEN=84 TOS=0x0 TTL=64 ID=38349DF
 3 TRACE: 2 fc475095 raw:PREROUTING:return:
 4 TRACE: 2 fc475095 raw:PREROUTING:policy:ACCEPT
 5 TRACE: 2 fc475095 filter:INPUT:return:
 6 TRACE: 2 fc475095 filter:INPUT:policy:DROP
 7 TRACE: 2 0df9d3d8 raw:PREROUTING:rule:0x3:CONTINUE \-4 \-t raw \-A PREROUTING \-p icmp \-j TRACE
.PP
The first line shows a packet entering rule set evaluation.
The protocol number is shown (AF_INET in this case), then a packet
identifier number that allows to correlate messages coming from rule set evaluation of
this packet.  After this, the rule that was matched by the packet is shown.
This is the TRACE rule that turns on tracing events for this packet.

The second line dumps information about the packet. Incoming interface
and packet headers such as source and destination addresses are shown.

The third line shows that the packet completed traversal of the raw table
PREROUTING chain, and is returning, followed by use the chain policy to make accept/drop
decision (the example shows accept being applied).
The fifth line shows that the packet leaves the filter INPUT chain, i.e., no rules in the filter tables
INPUT chain matched the packet.
It then got DROPPED by the policy of the INPUT table, as shown by line six.
The last line shows another packet arriving \-\- the packet id is different.

When using the TRACE target, it is usually a good idea to only select packets
that are relevant, for example via
.nf
iptables \-t raw \-A PREROUTING \-p tcp \-\-dport 80 \-\-syn \-m limit \-\-limit 1/s \-j TRACE
.fi
.TP
.B xtables-monitor \-\-event
  1 EVENT: nft: NEW table: table filter ip flags 0 use 4 handle 444
  2 EVENT: # nft: ip filter INPUT use 2 type filter hook input prio 0 policy drop packets 0 bytes 0
  3 EVENT: # nft: ip filter FORWARD use 0 type filter hook forward prio 0 policy accept packets 0 bytes 0
  4 EVENT: # nft: ip filter OUTPUT use 0 type filter hook output prio 0 policy accept packets 0 bytes 0
  5 EVENT: \-4 \-t filter \-N TCP
  6 EVENT: \-4 \-t filter \-A TCP \-s 192.168.0.0/16 \-p tcp \-m tcp \-\-dport 22 \-j ACCEPT
  7 EVENT: \-4 \-t filter \-A TCP \-p tcp \-m multiport \-\-dports 80,443 \-j ACCEPT
  8 EVENT: \-4 \-t filter \-A INPUT \-p tcp \-j TCP
  9 EVENT: \-4 \-t filter \-A INPUT \-m conntrack \-\-ctstate RELATED,ESTABLISHED \-j ACCEPT
 10 NEWGEN: GENID=13904 PID=25167 NAME=iptables-nftables-restore
.PP
This example shows event monitoring.  Line one shows creation of a table (filter in this case), followed
by three base hooks INPUT, FORWARD and OUTPUT.  The iptables-nftables tools all create tables and base
chains automatically when needed, so this is expected when a table was not yet initialized or when it is
re-created from scratch by iptables-nftables-restore.  Line five shows a new user-defined chain (TCP)
being added, followed by addition a few rules. the last line shows that a new ruleset generation has
become active, i.e., the rule set changes are now active.  This also lists the process id and the programs name.
.SH LIMITATIONS
.B xtables-monitor
only works with rules added using iptables-nftables, rules added using
iptables-legacy cannot be monitored.
.SH BUGS
Should be reported or by sending email to netfilter-devel@vger.kernel.org or
by filing a report on https://bugzilla.netfilter.org/.
.SH SEE ALSO
\fBiptables\fP(8), \fBxtables\fP(8), \fBnft\fP(8)