Talk:Iptables

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Starting iptables before network

Shouldn't this page explain how to set up systemd to start iptables before the network interfaces are up? I read Systemd and I will be trying this:

$ sudo vim /etc/systemd/system/network.service
[Unit]
Description=lan
Requires=iptables.service - added by me 
After=iptables.service - added by me 
Wants=network.target
Before=network.target
[Service]
Type=oneshot
RemainAfterExit=yes
EnvironmentFile=/etc/conf.d/network
ExecStart=/sbin/ip link set dev ${interface} up
ExecStart=/sbin/ip addr add ${address}/${netmask} broadcast ${broadcast} dev ${interface}
ExecStart=/sbin/ip route add default via ${gateway}
ExecStop=/sbin/ip addr flush dev ${interface}
ExecStop=/sbin/ip link set dev ${interface} down
[Install]
WantedBy=multi-user.target

however, I have no clue if this is correct or not. Doru001 (talk) 17:28, 27 January 2013 (UTC)

That's the way to do it. Consider adding "ip6tables.service" for IPv6 connections if it's required. A much cleaner and safer solution would be to have the actual iptables services start before any kind of network is available. This needs a "Before=sysinit.target" (and possibly more) listed in the Unit sections. If you could test it, I'm sure the iptables packager would be happy to hear from you at Bug #33478. --Gilrain (talk) 16:39, 8 February 2013 (UTC)
Following https://bugs.freedesktop.org/show_bug.cgi?id=57773#c7 from your bug report I have done this:
$ cat /usr/lib/systemd/system/iptables.service
[Unit]
Description=Packet Filtering Framework
DefaultDependencies=no
After=systemd-sysctl.service
Before=sysinit.target
[Service]
Type=oneshot
ExecStart=/usr/bin/iptables-restore /etc/iptables/iptables.rules
ExecReload=/usr/bin/iptables-restore /etc/iptables/iptables.rules
ExecStop=/usr/lib/systemd/scripts/iptables-flush
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target
Seems to be working, but I don't know how to check that it starts when it should, it is possible that journalctl is not started before it. Doru001 (talk) 14:53, 13 July 2013 (UTC)
Use "systemd-analyze plot > bootchart.svg" to check the complete start-up sequence. You should see iptables.service near the top, sysinit.target in the middle and network.target further down (at least, that what it looks like with UFW). Also, does iptables really need "After=systemd-sysctl.service" or is it there because of a quick copy-paste? --Gilrain (talk) 19:36, 13 July 2013 (UTC)
That was a quick copy-paste, but it makes sense to me to configure the kernel before iptables and iptables before sysinit. If you have a better iptables.service unit then please post it here. Thank you for systemd-analyze plot. Doru001 (talk) 08:58, 14 July 2013 (UTC)
Using Before=sysinit.target in this case would be wrong, it breaks dependencies between targets. Note that iptables.service is WantedBy=multi-user.target, multi-user.target is started after sysinit.target. I think the correct way to do this is by placing iptables.service into basic.target, which is started after sysinit.target but before multi-user.target. All services configuring network interfaces are in multi-user.target, so network.target is necessarily started after basic.target. -- Lahwaacz (talk) 17:40, 25 July 2013 (UTC)
Not really, WantedBy does not mean Before and in fact the start order is: iptables.service, sysinit.target and multi-user.target, with many other units started between them. See Requires in man systemd.unit. Not only that WantedBy has nothing to do with Before as many newcomers believe, but you confuse it with After. So this configuration says: if you start multi-user.target, then also start iptables.service. When should you start iptables.service? Before sysinit.target! I don't know what happens when sysinit.target is already started. And yes, systemd is uncomfortable, to say the least (join us on this). Doru001 (talk) 09:18, 4 September 2013 (UTC)

NAT Firewall

This is a combination of lazyness and the like, this is an old setup that I have since moved from this config to a hardware firewall. This setup is of a natting firewall with a few port forwards.

# Generated by iptables-save v1.3.5 on Tue Jun  5 19:52:40 2007
*raw
:PREROUTING ACCEPT [123119306:66686923721]
:OUTPUT ACCEPT [8218577:4064226432]
COMMIT
# Completed on Tue Jun  5 19:52:40 2007
# Generated by iptables-save v1.3.5 on Tue Jun  5 19:52:40 2007
*nat
:PREROUTING ACCEPT [1284892:103455725]
:POSTROUTING ACCEPT [708950:58789746]
:OUTPUT ACCEPT [81288:4974397]
:DNS - [0:0]
-A PREROUTING -p udp -m udp --dport 1337 -j DNAT --to-destination 10.0.0.42:1337 
-A PREROUTING -p udp -m udp --dport 54420 -j DNAT --to-destination 10.0.0.42:54420 
-A PREROUTING -p tcp -m tcp --dport 54420 -j DNAT --to-destination 10.0.0.42:54420 
-A PREROUTING -p tcp -m tcp --dport 54421 -j DNAT --to-destination 10.0.0.42:54421 
-A PREROUTING -p udp -m udp --dport 54421 -j DNAT --to-destination 10.0.0.42:54421 
-A PREROUTING -p udp -m udp --dport 7314 -j DNAT --to-destination 10.0.0.42:7314 
-A PREROUTING -p udp -m udp --dport 2424 -j DNAT --to-destination 10.0.0.42:2424 
-A PREROUTING -i eth3 -p tcp -m tcp --dport 3724 -j DNAT --to-destination 10.0.0.42:3724 
-A PREROUTING -p tcp -m tcp --dport 6881:6889 -j DNAT --to-destination 10.0.0.42 
-A POSTROUTING -o eth3 -j MASQUERADE 
COMMIT
# Completed on Tue Jun  5 19:52:40 2007
# Generated by iptables-save v1.3.5 on Tue Jun  5 19:52:40 2007
*mangle
:PREROUTING ACCEPT [123119304:66686924548]
:INPUT ACCEPT [8600443:3272731641]
:FORWARD ACCEPT [114518165:63414136121]
:OUTPUT ACCEPT [8218577:4064226432]
:POSTROUTING ACCEPT [122677262:67474602455]
COMMIT
# Completed on Tue Jun  5 19:52:40 2007
# Generated by iptables-save v1.3.5 on Tue Jun  5 19:52:40 2007
*filter
:INPUT ACCEPT [3327494:1199833518]
:FORWARD ACCEPT [1:0]
:OUTPUT ACCEPT [8211773:4063626894]
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT 
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT 
-A INPUT -i eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m multiport --dports 111,2049,4001,32764:32767 -j ACCEPT 
-A INPUT -p udp -m state --state NEW -m multiport --dports 111,2049,4001,32764:32767 -j ACCEPT 
-A INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT 
-A INPUT -p tcp -m tcp --dport 49152:65534 --tcp-flags FIN,SYN,RST,ACK SYN -j ACCEPT 
-A INPUT -p udp -m state --state NEW -m udp --dport 5353 -j ACCEPT 
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p udp -m udp --dport 1337 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p udp -m udp --dport 54420 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p tcp -m tcp --dport 54420 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p tcp -m tcp --dport 54421 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p udp -m udp --dport 54421 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p udp -m udp --dport 7314 -j ACCEPT 
-A FORWARD -d 10.0.0.42 -p udp -m udp --dport 2424 -j ACCEPT 
-A FORWARD -d 10.0.2.0/255.255.255.0 -i eth2 -j DROP 
-A FORWARD -d 10.0.1.0/255.255.255.0 -i eth1 -j DROP 
-A FORWARD -d 10.0.0.0/255.255.255.0 -i eth0 -j DROP 
-A FORWARD -d 10.0.0.0/255.255.255.0 -i eth3 -j ACCEPT 
-A FORWARD -d 10.0.1.0/255.255.255.0 -i eth3 -j ACCEPT 
-A FORWARD -d 10.0.2.0/255.255.255.0 -i eth3 -j ACCEPT 
-A FORWARD -s 10.0.0.0/255.255.255.0 -i eth0 -j ACCEPT 
-A FORWARD -s 10.0.1.0/255.255.255.0 -i eth1 -j ACCEPT 
-A FORWARD -s 10.0.2.0/255.255.255.0 -i eth2 -j ACCEPT 
-A FORWARD -s 10.0.0.42 -p tcp -m tcp --dport 6881:6999 -j ACCEPT 
-A FORWARD -s 192.168.1.2 -p tcp -m tcp --dport 6881:6889 -j ACCEPT 
COMMIT
# Completed on Tue Jun  5 19:52:40 2007

--Prometheanfire 14:31, 30 July 2009 (EDT)

I don't find this very useful, the Simple Stateful Firewall provides much more useful explanation. There are plenty of example iptables config files around. -- Lahwaacz (talk) 14:31, 21 August 2013 (UTC)