XTABLES-MONITOR(8) iptables 1.8.5 XTABLES-MONITOR(8)
NAME
xtables-monitor -- show changes to rule set and trace-events
SYNOPSIS
xtables-monitor [-t] [-e] [-4||-6]
DESCRIPTION
xtables-monitor is used to monitor changes to the ruleset or to show
rule evaluation events for packets tagged using the TRACE target. xta-
bles-monitor will run until the user aborts execution, typically by us-
ing CTRL-C.
OPTIONS
-e, --event
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.
-t, --trace
Watch for trace events generated by packets that have been
tagged using the TRACE target.
-4 Restrict output to IPv4.
-6 Restrict output to IPv6.
EXAMPLE OUTPUT
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
The first line shows a packet entering rule set evaluation. The proto-
col number is shown (AF_INET in this case), then a packet identifier
number that allows to correlate messages coming from rule set evalua-
tion 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 ta-
ble PREROUTING chain, and is returning, followed by use the chain pol-
icy to make accept/drop decision (the example shows accept being ap-
plied). 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
iptables -t raw -A PREROUTING -p tcp --dport 80 --syn -m limit --limit 1/s -j TRACE
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 for-
ward 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 RE-
LATED,ESTABLISHED -j ACCEPT
10 NEWGEN: GENID=13904 PID=25167 NAME=iptables-nftables-restore
This example shows event monitoring. Line one shows creation of a ta-
ble (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.
LIMITATIONS
xtables-monitor only works with rules added using iptables-nftables,
rules added using iptables-legacy cannot be monitored.
BUGS
Should be reported or by sending email to netfilter-devel@vger.ker-
nel.org or by filing a report on https://bugzilla.netfilter.org/.
SEE ALSO
iptables(8), xtables(8), nft(8)
iptables 1.8.5 XTABLES-MONITOR(8)