IptablesHowTo
Differences between revisions 1 and 12 (spanning 11 versions)
|
Size: 5044
Comment: imported from the old wiki
|
← Revision 12 as of 2008-08-06 16:25:16 ⇥
Size: 57
Comment: converted to 1.6 markup
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 1: | Line 1: |
| = IptablesHowTo = THIS IS NOT COMPLETE AND SHOULD BE COMPLETED BY SOMEONE WHO KNOWS MORE THAN ME! THANKS = Basic Iptables How to for Ubuntu Server Edition = Iptables is a firewall, installed by default on the Ubuntu Server (and maybe the regular setup? Someone else know?) There is a wealth of information available about iptables, but much of it is fairly complex, and if you want to do a few basic things, this How To is for you. == Basic Commands == Typing {{{ # iptables -L }}} lists your current rules in iptables. If you have just set up your server, you will have no rules, and you should see {{{ Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination }}} == Allowing Established Sessions == We can allow established sessions to receive traffic: {{{ # iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT }}} == Allowing Incoming Trafic on Specific Ports == You could start by blocking traffic, but you might be working over SSH, where you would need to allow SSH before blocking everything else. To allow incoming traffic on port 22 (traditionally used by SSH), you could tell iptables to allow all TCP traffic on port 22 of your network adapter. {{{ # iptables -A INPUT -p tcp -i eth0 --dport ssh -j ACCEPT }}} Specifically, this appends (-A) to the table INPUT the rule that any traffic to the interface (-i) eth0 on the destination port for ssh that iptables should jump (-j), or perform the action, ACCEPT. Lets check the rules: (only the first few lines shown, you will see more) {{{ # iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:ssh }}} Now, let's allow all web traffic {{{ # iptables -A INPUT -p tcp -i eth0 --dport 80 -j ACCEPT }}} Checking our rules, we have {{{ # iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:ssh ACCEPT tcp -- anywhere anywhere tcp dpt:www }}} We have specifically allowed tcp traffic to the ssh and web ports, but as we have not blocked anything, all traffic can still come in. == Blocking Traffic == Once a decision is made about a packet, no more rules affect it. As our rules allowing ssh and web trafic come first, as long as our rule to block all traffic comes after them, we can still accept the traffic we want. All we need to do is put the rule to block all traffic at the end. The -A command tells iptables to append the rule at the end, so we'll use that again. {{{ # iptables -A INPUT -j DROP # iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:ssh ACCEPT tcp -- anywhere anywhere tcp dpt:www DROP all -- anywhere anywhere }}} Because we didn't specify an interface or a protocol, any traffic for any port on any interface is blocked, except for web and ssh. == Editing iptables == The only problem with our setup so far is that even the loopback port is blocked. We could have written the drop rule for just eth0 by specifying -i eth0, but we could also add a rule for the loopback. If we append this rule, it will come too late - after all the traffic has been dropped. We need to insert this rule onto the fourth line. {{{ # iptables -I INPUT 4 -i lo -j ACCEPT # iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:ssh ACCEPT tcp -- anywhere anywhere tcp dpt:www ACCEPT all -- anywhere anywhere DROP all -- anywhere anywhere }}} The last two lines look nearly the same, so we will list iptables in greater detail. {{{ # iptables -L -v }}} == Further Information == [http://iptables-tutorial.frozentux.net/iptables-tutorial.html Iptables Tutorial] [http://www.netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.html Iptables How To] [http://www.netfilter.org/documentation/ Netfilter andn Iptables Multilingual Documentation] == Credits == Thanks to Rusty Russell and his How-To, as much of this is based off that. |
#REFRESH 0 http://help.ubuntu.com/community/IptablesHowTo |
IptablesHowTo (last edited 2008-08-06 16:25:16 by localhost)