Examples¶

High level abstractions¶

python-iptables implements a low-level interface that tries to closely match the underlying C libraries. The module iptc.easy improves the usability of the library by providing a rich set of high-level functions designed to simplify the interaction with the library, for example:

>>> import iptc
>>> iptc.easy.dump_table('nat', ipv6=False)
{'INPUT': [], 'OUTPUT': [], 'POSTROUTING': [], 'PREROUTING': []}
>>> iptc.easy.dump_chain('filter', 'OUTPUT', ipv6=False)
[{'comment': {'comment': 'DNS traffic to Google'},
  'counters': (1, 56),
  'dst': '8.8.8.8/32',
  'protocol': 'udp',
  'target': 'ACCEPT',
  'udp': {'dport': '53'}}]
>>> iptc.easy.add_chain('filter', 'TestChain')
True
>>> rule_d = {'protocol': 'tcp', 'target': 'ACCEPT', 'tcp': {'dport': '22'}}
>>> iptc.easy.insert_rule('filter', 'TestChain', rule_d)
>>> iptc.easy.dump_chain('filter', 'TestChain')
[{'protocol': 'tcp', 'target': 'ACCEPT', 'tcp': {'dport': '22'}}]
>>> iptc.easy.delete_chain('filter', 'TestChain', flush=True)

>>> # Example of goto rule // iptables -A FORWARD -p gre -g TestChainGoto
>>> iptc.easy.add_chain('filter', 'TestChainGoto')
>>> rule_goto_d = {'protocol': 'gre', 'target': {'goto': 'TestChainGoto'}}
>>> iptc.easy.insert_rule('filter', 'FORWARD', rule_goto_d)

Rules¶

In python-iptables, you usually first create a rule, and set any source/destination address, in/out interface and protocol specifiers, for example:

>>> import iptc
>>> rule = iptc.Rule()
>>> rule.in_interface = "eth0"
>>> rule.src = "192.168.1.0/255.255.255.0"
>>> rule.protocol = "tcp"

This creates a rule that will match TCP packets coming in on eth0, with a source IP address of 192.168.1.0/255.255.255.0.

A rule may contain matches and a target. A match is like a filter matching certain packet attributes, while a target tells what to do with the packet (drop it, accept it, transform it somehow, etc). One can create a match or target via a Rule:

>>> rule = iptc.Rule()
>>> m = rule.create_match("tcp")
>>> t = rule.create_target("DROP")

Match and target parameters can be changed after creating them. It is also perfectly valid to create a match or target via instantiating them with their constructor, but you still need a rule and you have to add the matches and the target to their rule manually:

>>> rule = iptc.Rule()
>>> match = iptc.Match(rule, "tcp")
>>> target = iptc.Target(rule, "DROP")
>>> rule.add_match(match)
>>> rule.target = target

Any parameters a match or target might take can be set via the attributes of the object. To set the destination port for a TCP match:

>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> match = rule.create_match("tcp")
>>> match.dport = "80"

To set up a rule that matches packets marked with 0xff:

>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> match = rule.create_match("mark")
>>> match.mark = "0xff"

Parameters are always strings. You can supply any string as the parameter value, but note that most extensions validate their parameters. For example this:

>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> rule.target = iptc.Target(rule, "ACCEPT")
>>> match = iptc.Match(rule, "state")
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> match.state = "RELATED,ESTABLISHED"
>>> rule.add_match(match)
>>> chain.insert_rule(rule)

will work. However, if you change the state parameter:

>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> rule.target = iptc.Target(rule, "ACCEPT")
>>> match = iptc.Match(rule, "state")
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> match.state = "RELATED,ESTABLISHED,FOOBAR"
>>> rule.add_match(match)
>>> chain.insert_rule(rule)

python-iptables will throw an exception:

Traceback (most recent call last):
  File "state.py", line 7, in <module>
    match.state = "RELATED,ESTABLISHED,FOOBAR"
  File "/home/user/Projects/python-iptables/iptc/ip4tc.py", line 369, in __setattr__
    self.parse(name.replace("_", "-"), value)
  File "/home/user/Projects/python-iptables/iptc/ip4tc.py", line 286, in parse
    self._parse(argv, inv, entry)
  File "/home/user/Projects/python-iptables/iptc/ip4tc.py", line 516, in _parse
    ct.cast(self._ptrptr, ct.POINTER(ct.c_void_p)))
  File "/home/user/Projects/python-iptables/iptc/xtables.py", line 736, in new
    ret = fn(*args)
  File "/home/user/Projects/python-iptables/iptc/xtables.py", line 1031, in parse_match
    argv[1]))
iptc.xtables.XTablesError: state: parameter error -2 (RELATED,ESTABLISHED,FOOBAR)

Certain parameters take a string that optionally consists of multiple words. The comment match is a good example:

>>> rule = iptc.Rule()
>>> rule.src = "127.0.0.1"
>>> rule.protocol = "udp"
>>> rule.target = rule.create_target("ACCEPT")
>>> match = rule.create_match("comment")
>>> match.comment = "this is a test comment"
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> chain.insert_rule(rule)

Note that this is still just one parameter value.

However, when a match or a target takes multiple parameter values, that needs to be passed in as a list. Let’s assume you have created and set up an ipset called blacklist via the ipset command. To create a rule with a match for this set:

>>> rule = iptc.Rule()
>>> m = rule.create_match("set")
>>> m.match_set = ['blacklist', 'src']

Note how this time a list was used for the parameter value, since the set match match_set parameter expects two values. See the iptables manpages to find out what the extensions you use expect. See ipset for more information.

When you are ready constructing your rule, add them to the chain you want it to show up in:

>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> chain.insert_rule(rule)

This will put your rule into the INPUT chain in the filter table.

Chains and tables¶

You can of course also check what a rule’s source/destination address, in/out inteface etc is. To print out all rules in the FILTER table:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> for chain in table.chains:
>>>     print "======================="
>>>     print "Chain ", chain.name
>>>     for rule in chain.rules:
>>>         print "Rule", "proto:", rule.protocol, "src:", rule.src, "dst:", \
>>>               rule.dst, "in:", rule.in_interface, "out:", rule.out_interface,
>>>         print "Matches:",
>>>         for match in rule.matches:
>>>             print match.name,
>>>         print "Target:",
>>>         print rule.target.name
>>> print "======================="

As you see in the code snippet above, rules are organized into chains, and chains are in tables. You have a fixed set of tables; for IPv4:

FILTER,
NAT,
MANGLE and
RAW.

For IPv6 the tables are:

FILTER,
MANGLE,
RAW and
SECURITY.

To access a table:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> print table.name
filter

To create a new chain in the FILTER table:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = table.create_chain("testchain")

$ sudo iptables -L -n
[...]
Chain testchain (0 references)
target     prot opt source               destination

To access an existing chain:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, "INPUT")
>>> chain.name
'INPUT'
>>> len(chain.rules)
10
>>>

More about matches and targets¶

There are basic targets, such as DROP and ACCEPT. E.g. to reject packets with source address 127.0.0.1/255.0.0.0 coming in on any of the eth interfaces:

>>> import iptc
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> rule = iptc.Rule()
>>> rule.in_interface = "eth+"
>>> rule.src = "127.0.0.1/255.0.0.0"
>>> target = iptc.Target(rule, "DROP")
>>> rule.target = target
>>> chain.insert_rule(rule)

To instantiate a target or match, we can either create an object like above, or use the rule.create_target(target_name) and rule.create_match(match_name) methods. For example, in the code above target could have been created as:

>>> target = rule.create_target("DROP")

instead of:

>>> target = iptc.Target(rule, "DROP")
>>> rule.target = target

The former also adds the match or target to the rule, saving a call.

Another example, using a target which takes parameters. Let’s mark packets going to 192.168.1.2 UDP port 1234 with 0xffff:

>>> import iptc
>>> chain = iptc.Chain(iptc.Table(iptc.Table.MANGLE), "PREROUTING")
>>> rule = iptc.Rule()
>>> rule.dst = "192.168.1.2"
>>> rule.protocol = "udp"
>>> match = iptc.Match(rule, "udp")
>>> match.dport = "1234"
>>> rule.add_match(match)
>>> target = iptc.Target(rule, "MARK")
>>> target.set_mark = "0xffff"
>>> rule.target = target
>>> chain.insert_rule(rule)

Matches are optional (specifying a target is mandatory). E.g. to insert a rule to NAT TCP packets going out via eth0:

>>> import iptc
>>> chain = iptc.Chain(iptc.Table(iptc.Table.NAT), "POSTROUTING")
>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> rule.out_interface = "eth0"
>>> target = iptc.Target(rule, "MASQUERADE")
>>> target.to_ports = "1234"
>>> rule.target = target
>>> chain.insert_rule(rule)

Here only the properties of the rule decide whether the rule will be applied to a packet.

Matches are optional, but we can add multiple matches to a rule. In the following example we will do that, using the iprange and the tcp matches:

>>> import iptc
>>> rule = iptc.Rule()
>>> rule.protocol = "tcp"
>>> match = iptc.Match(rule, "tcp")
>>> match.dport = "22"
>>> rule.add_match(match)
>>> match = iptc.Match(rule, "iprange")
>>> match.src_range = "192.168.1.100-192.168.1.200"
>>> match.dst_range = "172.22.33.106"
>>> rule.add_match(match)
>>> rule.target = iptc.Target(rule, "DROP")
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> chain.insert_rule(rule)

This is the python-iptables equivalent of the following iptables command:

# iptables -A INPUT -p tcp –destination-port 22 -m iprange –src-range 192.168.1.100-192.168.1.200 –dst-range 172.22.33.106 -j DROP

You can of course negate matches, just like when you use ! in front of a match with iptables. For example:

>>> import iptc
>>> rule = iptc.Rule()
>>> match = iptc.Match(rule, "mac")
>>> match.mac_source = "!00:11:22:33:44:55"
>>> rule.add_match(match)
>>> rule.target = iptc.Target(rule, "ACCEPT")
>>> chain = iptc.Chain(iptc.Table(iptc.Table.FILTER), "INPUT")
>>> chain.insert_rule(rule)

This results in:

$ sudo iptables -L -n
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0            MAC ! 00:11:22:33:44:55

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Counters¶

You can query rule and chain counters, e.g.:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, 'OUTPUT')
>>> for rule in chain.rules:
>>>         (packets, bytes) = rule.get_counters()
>>>         print packets, bytes

However, the counters are only refreshed when the underlying low-level iptables connection is refreshed in Table via table.refresh(). For example:

>>> import time, sys
>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, 'OUTPUT')
>>> for rule in chain.rules:
>>>         (packets, bytes) = rule.get_counters()
>>>         print packets, bytes
>>> print "Please send some traffic"
>>> sys.stdout.flush()
>>> time.sleep(3)
>>> for rule in chain.rules:
>>>         # Here you will get back the same counter values as above
>>>         (packets, bytes) = rule.get_counters()
>>>         print packets, bytes

This will show you the same counter values even if there was traffic hitting your rules. You have to refresh your table to get update your counters:

>>> import time, sys
>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, 'OUTPUT')
>>> for rule in chain.rules:
>>>         (packets, bytes) = rule.get_counters()
>>>         print packets, bytes
>>> print "Please send some traffic"
>>> sys.stdout.flush()
>>> time.sleep(3)
>>> table.refresh()  # Here: refresh table to update rule counters
>>> for rule in chain.rules:
>>>         (packets, bytes) = rule.get_counters()
>>>         print packets, bytes

What is more, if you add:

iptables -A OUTPUT -p tcp --sport 80
iptables -A OUTPUT -p tcp --sport 22

you can query rule and chain counters together with the protocol and sport(or dport), e.g.:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, 'OUTPUT')
>>> for rule in chain.rules:
>>>         for match in rule.matches:
>>>             (packets, bytes) = rule.get_counters()
>>>             print packets, bytes, match.name, match.sport

Autocommit¶

Python-iptables by default automatically performs an iptables commit after each operation. That is, after you add a rule in python-iptables, that will take effect immediately.

It may happen that you want to batch together certain operations. A typical use case is traversing a chain and removing rules matching a specific criteria. If you do this with autocommit enabled, after the first delete operation, your chain’s state will change and you have to restart the traversal. You can do something like this:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> removed = True
>>> chain = iptc.Chain(table, "FORWARD")
>>> while removed == True:
>>>     removed = False
>>>     for rule in chain.rules:
>>>         if rule.out_interface and "eth0" in rule.out_interface:
>>>             chain.delete_rule(rule)
>>>             removed = True
>>>             break

This is clearly not ideal and the code is not very readable. An alternative is to disable autocommits, traverse the chain, removing one or more rules, than commit it:

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> table.autocommit = False
>>> chain = iptc.Chain(table, "FORWARD")
>>> for rule in chain.rules:
>>>     if rule.out_interface and "eth0" in rule.out_interface:
>>>         chain.delete_rule(rule)
>>> table.commit()
>>> table.autocommit = True

The drawback is that Table is a singleton, and if you disable autocommit, it will be disabled for all instances of that Table.

Easy rules with dictionaries¶

To simplify operations with python-iptables rules we have included support to define and convert Rules object into python dictionaries.

>>> import iptc
>>> table = iptc.Table(iptc.Table.FILTER)
>>> chain = iptc.Chain(table, "INPUT")
>>> # Create an iptc.Rule object from dictionary
>>> rule_d = {'comment': {'comment': 'Match tcp.22'}, 'protocol': 'tcp', 'target': 'ACCEPT', 'tcp': {'dport': '22'}}
>>> rule = iptc.easy.encode_iptc_rule(rule_d)
>>> # Obtain a dictionary representation from the iptc.Rule
>>> iptc.easy.decode_iptc_rule(rule)
{'tcp': {'dport': '22'}, 'protocol': 'tcp', 'comment': {'comment': 'Match tcp.22'}, 'target': 'ACCEPT'}

Known Issues¶

These issues are mainly caused by complex interaction with upstream’s Netfilter implementation, and will require quite significant effort to fix. Workarounds are available.

The hashlimit match requires explicitly setting hashlimit_htable_expire. See Issue #201.
The NOTRACK target is problematic; use CT --notrack instead. See Issue #204.