iptables

Iptables Input Plugin

The iptables plugin gathers packets and bytes counters for rules within a set of table and chain from the Linux's iptables firewall.

Rules are identified through associated comment. Rules without comment are ignored. Indeed we need a unique ID for the rule and the rule number is not a constant: it may vary when rules are inserted/deleted at start-up or by automatic tools (interactive firewalls, fail2ban, ...). Also when the rule set is becoming big (hundreds of lines) most people are interested in monitoring only a small part of the rule set.

Before using this plugin you must ensure that the rules you want to monitor are named with a unique comment. Comments are added using the -m comment --comment "my comment" iptables options.

The iptables command requires CAP_NET_ADMIN and CAP_NET_RAW capabilities. You have several options to grant telegraf to run iptables:

• Run telegraf as root. This is strongly discouraged.
• Configure systemd to run telegraf with CAP_NET_ADMIN and CAP_NET_RAW. This is the simplest and recommended option.
• Configure sudo to grant telegraf to run iptables. This is the most restrictive option, but require sudo setup.

Using systemd capabilities

You may run systemctl edit telegraf.service and add the following:

[Service]
CapabilityBoundingSet=CAP_NET_RAW CAP_NET_ADMIN
AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN

Since telegraf will fork a process to run iptables, AmbientCapabilities is required to transmit the capabilities bounding set to the forked process.

Using sudo

You will need the following in your telegraf config:

[[inputs.iptables]]
  use_sudo = true

You will also need to update your sudoers file:

$ visudo
# Add the following line:
Cmnd_Alias IPTABLESSHOW = /usr/bin/iptables -nvL *
telegraf  ALL=(root) NOPASSWD: IPTABLESSHOW
Defaults!IPTABLESSHOW !logfile, !syslog, !pam_session

Using IPtables lock feature

Defining multiple instances of this plugin in telegraf.conf can lead to concurrent IPtables access resulting in "ERROR in input [inputs.iptables]: exit status 4" messages in telegraf.log and missing metrics. Setting 'use_lock = true' in the plugin configuration will run IPtables with the '-w' switch, allowing a lock usage to prevent this error.

Configuration:

  # use sudo to run iptables
  use_sudo = false
  # run iptables with the lock option
  use_lock = false
  # Define an alternate executable, such as "ip6tables". Default is "iptables".
  # binary = "ip6tables"
  # defines the table to monitor:
  table = "filter"
  # defines the chains to monitor:
  chains = [ "INPUT" ]

Measurements & Fields:

• iptables
  • pkts (integer, count)
  • bytes (integer, bytes)

Tags:

• All measurements have the following tags:
  • table
  • chain
  • ruleid

The ruleid is the comment associated to the rule.

Example Output:

$ iptables -nvL INPUT
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source               destination
100   1024   ACCEPT     tcp  --  *      *       192.168.0.0/24       0.0.0.0/0            tcp dpt:22 /* ssh */
 42   2048   ACCEPT     tcp  --  *      *       192.168.0.0/24       0.0.0.0/0            tcp dpt:80 /* httpd */

$ ./telegraf --config telegraf.conf --input-filter iptables --test
iptables,table=filter,chain=INPUT,ruleid=ssh pkts=100i,bytes=1024i 1453831884664956455
iptables,table=filter,chain=INPUT,ruleid=httpd pkts=42i,bytes=2048i 1453831884664956455