iptables wrapper for easy management of dual-stack (ipv4/ipv6) firewall configuration
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trilobite: iptables wrapper for easy management of dual-stack (ipv4/ipv6) firewall configuration

Deprecation Warning: Since Linux kernel 3.13+ (2014), nft/nftables is a superior replacement that has nice dual-stack configuration support, and should probably be used instead of scripts such as this one.

Yet another iptables wrapper, aiming to keep simple, clear and minimalistic state of dual-stack firewall in a DRY yaml configuration file, featuring as little differences from lower-level (iptables) syntax as possible, atomic updates, plain diffs of current state vs config, ruleset backups and various fallbacks to make sure I don't accidentally lock myself out of the machine.

Code is a bag of hacks in huge loops piled on over time, to be eventually scrapped in favor of nftables bpf-based filters.


YAML config gets parsed into two iptables-save/restore dumps (one for IPv4, another for IPv6). Each line gets expanded w/ appropriate modules, chain name and jump-action. Script decides which rules should be omitted in v4/v6 dump by looking at IP format and optional -v4/-v6 flag.

After that, it pulls the old tables via iptables-save to tmp buffer and tries to feed the new ones to iptables-restore, which will atomically apply all new rules if there are no errors in any of them.

If new tables got applied, it dumps the them again, comparing then to the old dump to see if there are any diffirences (aside from comments and packet counters).

Then old-vs-new diff can be generated with --summary option, backups will be made/rotated and, unless --no-revert option is specified, "at" will be used to schedule rules' revert in a few minutes, which should be disabled manually, if ssh (or whatever access) wasn't accidentally blocked by the new rules.


Chains, policies and generic rules

Should be pretty intuitive from the yaml example, otherwise some parts are explained below.

If there's no explicit --state spec in rule, ALL rules will get "-m state --state NEW". Basically, that means that all such rules act on per-connection (as opposed to per-packet) basis by default. That can be disabled via "stateful" configuration switch.

Start of the rule definitions section and filter table init - you can actually replace chain definition, like "input:" by "input/-" to set policy to DROP, or "somechain/x" for REJECT, "/+" for ACCEPT, same as for rules.

There are also special "somechain/4" and "somechain/6" policy specs, which mean "ACCEPT for v4, DROP for v6" and the reverse thing respectively.

			- -v4 -p icmp
			- -v6 -p icmpv6

Three rules in input, first in this chain, will be same as...

$IPT4 -t filter -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
$IPT6 -t filter -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
$IPT4 -t filter -A INPUT -p icmp -j ACCEPT
$IPT6 -t filter -A INPUT -p icmp6 -j ACCEPT

...generally-used bash code will produce.

Note the "-v4" and "-v6" switches and that "-j ACCEPT" is added by default to non-empty rules (which are special, and mean "-j DROP") if no "-", "x", "<" or "|" specified in the end.

Empty chain definitions (as with "output" here) are fine, too.

	- -i vde -s 2001:470:1f0b:11de::20/124
	- <

Custom chain definition. First line will go to ipv6 table only, second is the special magic syntax (one of a few) for "-j RETURN", which will produce passthrough chain in ipv4 and a check for ipv6.

- -i lan -s --mac-source 00:11:6b:28:7f:68 # wlan.v4c

Won't need "-m mac", since it's quite obvious that it should be present here, and it will be added to the final rule. Note the comment - it's valid yaml comment, and won't be parsed.

# Azureus to coercion
- -p tcp/udp -d --dport 28637
- -p udp -d --dport 28638

# Outgoing p2p traffic
- -p tcp/udp --gid-owner p2p/transmission/mldonkey

Any number of "-p proto1/proto2..." will be expanded as multiple rules, one for each protocol, as with tcp/udp in this case. Same goes for other convenience expansions - "--sport/dport" (common in stateless rulesets/chains/protos), "--uid-owner a/b/c", etc.

Basically it's all accomplised by a bunch of regexes, ran over rules:

extend_modules = {
	'--mac-source': 'mac',
	'--state': 'state',
	'--(src|dst)-range': 'iprange',
	'--[sd]port\s+(\S+,)+\S+': 'multiport',
	'--match-set': 'set',
	'--pkt-type': 'pkttype',
	'--[ug]id-owner': 'owner',

extend_duplicate = [

See beginning of the script for the up-to-date list of these.

- -p tcp -d 2001:470:1f0a:11de::2
# Cut the rest

Yep, last one is an empty rule, which will be interpreted as "-" - "-j DROP".

- +
- x

Briefly described above syntax magic - expands to "-j ACCEPT" and "-j REJECT" respectively.

Service rules

		input-lo: +
		output-lo: +

Start of "services" section.

Here rules can be grouped on per-service (or purpose) basis by specific service. Service name/purpose will go into the resulting dump as a comment.

Service rules get added to the specified chains in order they appear in the configuration file. Again, it's probably more obvious in example config.

"input-lo" here is "-" specification - it's valid for input/output chains, and will add "-i interface" or "-o interface" to each rule specified inside.

"+" is just a yaml string (expands to "-j ACCEPT"), instead of dict ("name: ...") or list ("- ...") notation, seen above. String will just be parsed as one rule, so there's no need to make a lists for one-liners.

Result of these should be roughly this:

$IPT4 -A INPUT -i lo -m state --state NEW -j ACCEPT
$IPT6 -A INPUT -i lo -m state --state NEW -j ACCEPT
$IPT4 -A OUTPUT -o lo -m state --state NEW -j ACCEPT
$IPT6 -A OUTPUT -o lo -m state --state NEW -j ACCEPT

"-j action/chain" works as in vanilla tables:

		input-lan: -j core_in
		output-lan: -j core_out

Just an svc name with a simple allow-all ipv6 rule:

	6to4_forwarding: -v6 -i tot

Such rules will go into INPUT chain by default.

			- -s -
			- -s -
			- -d -
			- -d -

Bunch of IPv4 DROP rules for ppp2 interface.

	ssh: -p tcp --dport ssh

Simple "open port" rule (for ssh on port 22, in this case), sufficient for 90% of services.

	mail: -p tcp --dport smtp,pop3,imap,pop3s,imaps

"-m multiport" will be added here.

			- -s x
			- -s x
			- -v4

All for ip4tables. Last one is "-j DROP".

	finish: x

Can be a last "reject-everything-else" rule.

There's also support for ipsets and some other modules. Check out the beginning of the code for up2date expansion definitions.


Only special syntax which is not translated to iptables at all atm is "--metrics" switch:

	mcast: --pkt-type multicast --metrics media.packets
	pulse: -s -p tcp --dport 4712,4713 --metrics pulse.connz/media.packets

It builds a special file (location can be specified in config) with the "table chain rule_number name" syntax, example:

filter INPUT 8 media.packets
filter INPUT 12 sshd.connz
filter INPUT 13 media.packets
filter INPUT 13 pulse.connz

...which can be used later with netfilter counters (think "iptables -L INPUT -vn") to produce stats for specific types of traffic on a local machine.

Note that since 99% of tcp packets (all, except syn) are usually matched by some "--state RELATED,ESTABLISHED" rule, "pulse" rule above will only count syn packets (new connections), not the actual traffic.

It's to count connections' traffic as well, it's possible to use "--metrics-track" magic, with following section in the config:

	enabled: true
	table: filter
	chain: conn_metrics
	shift: 0

So a rule like this:

pulse: -s -p tcp --dport 4712,4713 --metrics-track media.packets

Will be transformed into a following set of rules:

-A conn_metrics -m connmark --mark 0x1/0x1
-A INPUT -s -p tcp -m multiport --dport 4712,4713 -j CONNMARK --or-mark 0x1
-A INPUT -s -p tcp -m multiport --dport 4712,4713 -j ACCEPT

With metrics, defined as:

filter conn_metrics 1 media.packets
filter INPUT 8 media.packets

Thus, allowing to count all the packets and bytes in the connection (by piping them through "conn_metrics" chain before accepting by --state rule), while retaining a stateful configuration for the firewall (i.e. making pass/filter decisions on per-connection, not per-packet, basis). See the comments in example config for more details on the metrics_conntrack section.

Quick manual non-critical rule disabling

Rules can have --try option in them, in which case these rules will be disabled if --skip-tries (-e) option is specified.

My use-case is not-so-important rules, depending on the DNS availability - some single-ip hosts on the internet. If link is currently down, iptables will fail to apply the whole ruleset, which is much worse than just skipping these particular rules until the link will be restored.

Naturally, option itself will never be passed to iptables.


WIth --jinja2 option, configuration file will be processed by jinja2, before parsed as yaml.

See jinja2 documentation for template syntax description.

Parameters passed to template.render():

  • hosts - /etc/hosts as a mapping.

    For example, hosts-file line sub.host.example.org will produce following mapping (presented as yaml):

  • cfg - whatever is in --jinja2-config yaml, if passed, else None.

Extra filters/tags available:

  • dns filter - will use socket.getaddrinfo() to resolve hostname into unique address.

    One optional argument is address family: "inet" or "inet6".

    If name resolves to non-unique address or doesn't resolve - exception will be raised (use --debug for more details, socket.gaierror's are remarkably non-informative), --try feature can be used to just skip rules that aren't critical in such cases, also see --replace-dns fallback option.

Templating requirement (or any other commandline option for that matter) can be specified as emacs-local-var-style # -*- jinja2: true -*- headers (parsed as yaml) at the first line(s) of the script.

Templating result as well as passed template context values can be dumped with --jinja-dump flag.


Uses PyYAML module along with iptables and ipset binaries.

Jinja2 is only required if --jinja2 opton is used.