Ubuntu Manpages

sanewall-actions, sanewall-accept, sanewall-deny, sanewall-drop,

accept

accept with limit requests/period burst [overflow action]

accept with recent name seconds hits

accept with knock name

reject [with message]

drop

deny

return

tarpit

These actions are the actions to be taken on traffic that has been matched by a particular rule.

Sanewall will also pass through any actions that iptables(8) accepts, however these definitions provide lowercase versions which accept arguments where appropriate and which could otherwise not be passed through.


Note

The iptables(8) LOG action is best used through the optional rule parameter log since the latter can be combined with one of these actions (Sanewall will generate multiple firewall rules to make this happen). For information on log and loglimit, see optional rule parameters: sanewall-rule-params(5).

The following actions are defined:

accept

accept allows the traffic matching the rules to reach its destination.

For example, to allow SMTP requests and their replies to flow:

server smtp accept

accept with limit

accept with limit allows the traffic, with new connections limited to requests/period with a maximum burst. Run iptables -m limit --help for more information.

The default overflow action is to REJECT the excess connections (DROP would produce timeouts on otherwise valid service clients).

Examples:

server smtp accept with limit 10/sec 100
server smtp accept with limit 10/sec 100 overflow drop

accept with recent

accept with recent allows the traffic matching the rules to reach its destination, limited per remote IP to hits per seconds. Run iptables -m recent --help for more information.

The name parameter is used to allow multiple rules to share the same table of recent IPs.

For example, to allow only 2 connections every 60 seconds per remote IP, to the smtp server:

server smtp accept with recent mail 60 2


Note
When a new connection is not allowed, the traffic will continue to be matched by the rest of the firewall. In other words, if the traffic is not allowed due to the limitations set here, it is not dropped, it is just not matched by this rule.

accept with knock

accept with knock allows easy integration with knockd[1], a server that allows you to control access to services by sending certain packets to "knock" on the door, before the door is opened for service.

The name is used to build a special chain knock_<name> which contains rules to allow established connections to work. If knockd has not allowed new connections any traffic entering this chain will just return back and continue to match against the other rules until the end of the firewall.

For example, to allow HTTPS requests based on a knock write:

server https accept with knock hidden

then configure knockd to enable the HTTPS service with:

iptables -A knock_hidden -s %IP% -j ACCEPT

and disable it with:

iptables -D knock_hidden -s %IP% -j ACCEPT

You can use the same knock name in more than one Sanewall rule to enable/disable all the services based on a single knockd configuration entry.


Note
There is no need to match anything other than the IP in knockd. Sanewall already matches everything else needed for its rules to work.

reject with message, reject

reject discards the traffic matching the rules and sends a rejecting message back to the sender.

When used with with the specific message to return can be specified. Run iptables -j REJECT --help for a list of the --reject-with values which can be used for message. See the section called “REJECT WITH MESSSAGES” for some examples.

The default (no message specified) is to send tcp-reset when dealing with TCP connections and icmp-port-unreachable for all other protocols.

For example:

UNMATCHED_INPUT_POLICY="reject with host-prohib"
policy reject with host-unreach
server ident reject with tcp-reset

drop, deny

drop discards the traffic matching the rules. It does so silently and the sender will need to timeout to conclude it cannot reach the service.

deny is a synonym for drop. For example, either of these would silently discard SMTP traffic:

server smtp drop
server smtp deny

return

return will return the flow of processing to the parent of the current command.

Currently, the only time return can be used meaningfully used is as a policy for an interface definition. Unmatched traffic will continue being processed with the possibility of being matched by a later definition. For example:

policy return

tarpit

tarpit captures and holds incoming TCP connections open.

Connections are accepted and immediately switched to the persist state (0 byte window), in which the remote side stops sending data and asks to continue every 60-240 seconds.

Attempts to close the connection are ignored, forcing the remote side to time out the connection after 12-24 minutes.

Example:

server smtp tarpit


Note
As the kernel conntrack modules are always loaded by Sanewall, some per-connection resources will be consumed. See this bug report[2] for details.

The following actions also exist but should not be used under normal circumstances:

mirror

mirror returns the traffic it receives by switching the source and destination fields. REJECT will be used for traffic generated by the local host.


Warning
The MIRROR target was removed from the Linux kernel due to its security implications.

MIRROR is dangerous; use it with care and only if you understand what you are doing.

redirect, redirect to-port port

redirect is used internally by Sanewall helper commands.

Only Sanewall developers should need to use this action directly.

The following RFCs contain information relevant to these messages:


RFC 1812[3]


RFC 1122[4]


RFC 792[5]

icmp-net-unreachable, net-unreach

ICMP network unreachable

Generated by a router if a forwarding path (route) to the destination network is not available.

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 792.


Note
Use with care. The sender and the routers between you and the sender may conclude that the whole network your host resides in is unreachable, and prevent other traffic from reaching you.

icmp-host-unreachable, host-unreach

ICMP host unreachable

Generated by a router if a forwarding path (route) to the destination host on a directly connected network is not available (does not respond to ARP).

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 792.


Note
Use with care. The sender and the routers between you and the sender may conclude that your host is entirely unreachable, and prevent other traffic from reaching you.

icmp-proto-unreachable, proto-unreach

ICMP protocol unreachable

Generated if the transport protocol designated in a datagram is not supported in the transport layer of the final destination.

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 792.

icmp-port-unreachable, port-unreach

ICMP port unreachable

Generated if the designated transport protocol (e.g. TCP, UDP, etc.) is unable to demultiplex the datagram in the transport layer of the final destination but has no protocol mechanism to inform the sender.

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 792.

Generated by hosts to indicate that the required port is not active.

icmp-net-prohibited, net-prohib

ICMP communication with destination network administratively prohibited

This code was intended for use by end-to-end encryption devices used by U.S. military agencies. Routers SHOULD use the newly defined Code 13 (Communication Administratively Prohibited) if they administratively filter packets.

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 1122.


Note
This message may not be widely understood.

icmp-host-prohibited, host-prohib

ICMP communication with destination host administratively prohibited

This code was intended for use by end-to-end encryption devices used by U.S. military agencies. Routers SHOULD use the newly defined Code 13 (Communication Administratively Prohibited) if they administratively filter packets.

From RFC 1812, section 5.2.7.1. See RFC 1812 and RFC 1122.


Note
This message may not be widely understood.

tcp-reset

TCP RST

The port unreachable message of the TCP stack.

See RFC 1122.


Note
tcp-reset is useful when you want to prevent timeouts on rejected TCP services where the client incorrectly ignores ICMP port unreachable messages.

Sanewall program: sanewall(1)
Sanewall configuration: sanewall.conf(5)
interface definition: sanewall-interface(5)
router definition: sanewall-router(5)
optional rule parameters: sanewall-rule-params(5)

Sanewall Team

Copyright © 2012, 2013 Phil Whineray <phil@sanewall.org>

1.
knockd
http://www.zeroflux.org/knock/
2.
bug report
http://bugs.sanewall.org/sanewall/issues/10
3.
RFC 1812
http://www.ietf.org/rfc/rfc1812.txt
4.
RFC 1122
http://www.ietf.org/rfc/rfc1122.txt
5.
RFC 792
http://www.ietf.org/rfc/rfc0792.txt