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Amazon iptables Manual & Tutorial
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Amazon iptables Manual & Tutorial

Amazon iptables Manual & Tutorial

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An iptables guide & tutorial - iptablesrocks.org
Welcome to iptablesrocks.org! Iptablesrocks was created to provide a publicly available, easy to understand guide and tutorial for the installation and
configuration of iptables. Iptables is a linux package for managing IPv4 (and optionally IPv6) packet filtering and NAT (Network Address Translation).
Iptables can be configured to function as a firewall, a NAT mechanism, a packet filter or all 3 at once. The diversity of capabilities possible with iptables
makes it a secure, stable and economical alterative to hardware based firewalls and routers or costly 3rd party firewall software. Iptables can also
serve as a rendundant firewall in conjunction with a hardware firewall, providing you with an extra layer of security. Iptablesrocks.org covers the
installation of iptables in a Redhat environment, the syntax and structure associated with iptables and a collection a pre-configured iptables
configurations for a variety of applications. This site is currently under development. Enjoy!
The iptablesrocks.org iptables firewall setup guide
An overview of the iptablesrocks firewall
Step 1:
System requirements & Pre-configuration
Step 2:
Deploying a safety net.
Step 3:
The iptables firewall ruleset
Step 4:
Testing functionality
Step 5:
Installing Iptables Log Analyzer
Step 6:
Maintaining & modifying your firewall and starting it on boot
Step 7:
Feedback
A word of advise: Before you make any changes to your iptables configuration, you should read about
http://www.iptablesrocks.org/ [2/13/2004 8:04:42 PM]
home
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syntax & structure
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examples
Welcome to Iptablesrocks.org
2666
home
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syntax & structure
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Site last modified:
February 13, 2004 15:27:51
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contact
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Quick links to need specific iptables configurations
general web server firewall
linux gateway w/DSL connection
linux gateway w/Cable connection
sever to server trusted connections
pre-configuration precautions!
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faq
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Summary of Contents for Amazon iptables

  • Page 1 Iptables is a linux package for managing IPv4 (and optionally IPv6) packet filtering and NAT (Network Address Translation). Iptables can be configured to function as a firewall, a NAT mechanism, a packet filter or all 3 at once. The diversity of capabilities possible with iptables makes it a secure, stable and economical alterative to hardware based firewalls and routers or costly 3rd party firewall software.

  • Page 2: Syntax & Structure

    -R [chain] - Replace an existing rule from a desired chain in the current configuration iptables - I [chain] - (that's a capital I as in Insert) Insert a new rule into a desired chain of the current configuration...
  • Page 3 Iptablesrocks.org - Syntax & Structure Site last modified: February 13, 2004 15:27:51 http://www.iptablesrocks.org/syntax/ (2 of 2) [2/13/2004 8:04:43 PM]...
  • Page 4 When running a typical web server, you need a firewall that is secure and offers protection, but you also need one that allows all needed traffic to be able to enter and leave the server so that your server's day to day operations can carry on unimpeded. This particular iptables configuration does the following: 1.
  • Page 5 Iptablesrocks.org - Examples http://www.iptablesrocks.org/examples/ (2 of 2) [2/13/2004 8:04:44 PM]...

  • Page 6: Frequently Asked Questions

    Q: How do I export my server's iptables rulset to flat iptables script? A: The command "iptables-save > /path/to/firewall_script" will export the current iptables ruleset to a flat file called "firewall_script". Q: I've installed the iptablesrocks.org firewall and it's working, but now I cannot telnet to my server! What's wrong? A: The iptablesrocks.org firewall does not allow telnet connections on port 23 by default.
  • Page 7 Iptablesrocks.org - Contact home syntax & structure examples contact links Contact Iptablesrocks.org If you would like to contact me, please fill out the form below and then click "Send It!". Your name: Your e-mail: Comments/Questions: Send It! home syntax & structure examples contact links...
  • Page 8 Iptablesrocks.org - Links home syntax & structure examples contact links Links A collection of useful links. The Netfilter/Iptables Project - http://www.netfilter.org/ Linuxguruz Iptables Tutorial - http://www.linuxguruz.com/iptables/howto/iptables-HOWTO.html Qmailrocks.org - My qmail installation guide Djbdnsrocks.org - My djbdns installation guide home syntax & structure...
  • Page 9 Maintenance Maintaining your iptables firewall is pretty easy. The only thing you will want to keep an eye on is the logs at /var/log/firewall. The logs can let you know when your server is being probed or when an attack is being attempted, this allowing you to take appropriate action. Once you start viewing your logs, you are going to notice that almost every hour of every day someone is going to be trying to gain access to your server, find an exploit on your server or attack your server.
  • Page 10 Well, if you wanted to close port 143, all you would have to do is edit the firewall script at /root/primary_firewall and remove that line. Once the line is gone and you've saved the changes, you would activate the change by re-importing the firewall script back into the iptables ruleset like so :iptables-restore <...
  • Page 11 (man iptables) for the whole gamut. As I said before, always make sure you enable your iptables "safetynet" before you start playing with your firewall setup. You don't want to accdientally lock yourself out of your server! Starting your fiewall on boot The final part of this setup guide will cover the integration of your firewall into the server's boot process.
  • Page 12 The iptablesrocks.org iptables firewall setup guide Feedback: Now that you've finished the iptablesrocks.org iptables setup guide, please provide me with some feedback. What do you think of the setup guide? It stinks! Not very good It was ok...
  • Page 13 In this way, should I screw up at some point and lock myself out of my server, I will only need to wait a maximum of 10 minutes before the bad firewall rules will be dropped and I'll be able to shell into my server again. If you are a newbie at iptables, or even a seasoned pro, this little safety measure can be a lifesaver.
  • Page 14 "accept all" state where it accepts any incoming, outgoing and forward packet requests. You certainly do not want to leave this crontab running if you are not actively working on your iptables configuration. The sole of this crontab is to provide a safety net should you accidentally screw up and lock yourself out of your server while you are implementing or testing new iptables configurations.
  • Page 15 # import this saved configuration into your iptables configuration with the following command: # iptables-restore < web_server.config *nat :PREROUTING ACCEPT [127173:7033011] :POSTROUTING ACCEPT [31583:2332178] :OUTPUT ACCEPT [32021:2375633] COMMIT *mangle :PREROUTING ACCEPT [444:43563] :INPUT ACCEPT [444:43563] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [402:144198]...
  • Page 16 -A OUTPUT -d 127.0.0.1 -j ACCEPT -A OUTPUT -p icmp -j icmp_packets -A OUTPUT -j LOG --log-prefix "IPTABLES-OUT Default Drop: " --log-level 7 -A icmp_packets -p icmp -m icmp --icmp-type 0 -j ACCEPT -A icmp_packets -s 127.0.0.1 -p icmp -m icmp --icmp-type 8 -j ACCEPT...
  • Page 17 [-t table] -E old-chain-name new-chain-name DESCRIPTION Iptables is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains.
  • Page 18 Manpage of IPTABLES A firewall rule specifies criteria for a packet, and a target. If the packet does not match, the next rule in the chain is the examined; if it does match, then the next rule is specified by the value of the target, which can be the name of a user-defined chain or one of the special values ACCEPT, DROP, QUEUE, or RETURN.
  • Page 19 List all rules in the selected chain. If no chain is selected, all chains are listed. As every other iptables command, it applies to the specified table (filter is the default), so NAT rules get listed by iptables -t nat -n -L Please note that it is often used with the -n option, in order to avoid long reverse DNS lookups.
  • Page 20 Manpage of IPTABLES -N, --new-chain chain Create a new user-defined chain by the given name. There must be no target of that name already. -X, --delete-chain [chain] Delete the optional user-defined chain specified. There must be no references to the chain. If there are, you must delete or replace the referring rules before the chain can be deleted.

  • Page 21: Other Options

    Manpage of IPTABLES option is omitted in a rule, then matching the rule will have no effect on the packet's fate, but the counters on the rule will be incremented. -i, --in-interface [!] name Name of an interface via which a packet is going to be received (only for packets entering the INPUT, FORWARD and PREROUTING chains).

  • Page 22: Match Extensions

    MATCH EXTENSIONS iptables can use extended packet matching modules. These are loaded in two ways: implicitly, when -p or --protocol is specified, or with the -m or --match options, followed by the matching module name; after these, various extra command line options become available, depending on the specific module. You can specify multiple extended match modules in one line, and you can use the -h or --help options after the module has been specified to receive help specific to that module.
  • Page 23 This allows specification of the ICMP type, which can be a numeric ICMP type, or one of the ICMP type names shown by the command iptables -p icmp -h --mac-source [!] address Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets coming from an Ethernet device and entering the PREROUTING, FORWARD or INPUT chains.
  • Page 24 Manpage of IPTABLES limit This module matches at a limited rate using a token bucket filter. A rule using this extension will match until this limit is reached (unless the `!' flag is used). It can be used in combination with the LOG target to give limited logging, for example.
  • Page 25 --cmd-owner name Matches if the packet was created by a process with the given command name. (this option is present only if iptables was compiled under a kernel supporting this feature) state This module, when combined with connection tracking, allows access to the connection tracking state for this packet.
  • Page 26 Manpage of IPTABLES This module, when combined with connection tracking, allows access to more connection tracking information than the "state" match. (this module is present only if iptables was compiled under a kernel supporting this feature) --ctstate state Where state is a comma separated list of the connection states to match. Possible states are...
  • Page 27 This module matches the 8 bits of Type of Service field in the IP header (ie. including the precedence bits). --tos tos The argument is either a standard name, (use iptables -m tos -h to see the list), or a numeric value to match. This module matches the SPIs in AH header of IPSec packets. --ahspi [!] spi[:spi] This module matches the SPIs in ESP header of IPSec packets.

  • Page 28: Target Extensions

    TARGET EXTENSIONS iptables can use extended target modules: the following are included in the standard distribution. Turn on kernel logging of matching packets. When this option is set for a rule, the Linux kernel will print some information on all matching packets (like most IP header fields) via the kernel log (where it can be read with dmesg or syslogd(8)).
  • Page 29 This is used to set the 8-bit Type of Service field in the IP header. It is only valid in the mangle table. --set-tos tos You can use a numeric TOS values, or use iptables -j TOS -h http://www.iptablesrocks.org/syntax/man_iptables.htm (13 of 20) [2/13/2004 8:04:51 PM]...
  • Page 30 Manpage of IPTABLES to see the list of valid TOS names. MIRROR This is an experimental demonstration target which inverts the source and destination fields in the IP header and retransmits the packet. It is only valid in the INPUT, FORWARD and PREROUTING chains, and user-defined chains which are only called from those chains.
  • Page 31 Manpage of IPTABLES You can add several --to-destination options. If you specify more than one destination address, either via an address range or multiple --to-destination options, a simple round-robin (one after another in cycle) load balancing takes place between these adresses.
  • Page 32 2) Small mail works fine, but large emails hang. 3) ssh works fine, but scp hangs after initial handshaking. Workaround: activate this option and add a rule to your firewall configuration like: iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \ -j TCPMSS --clamp-mss-to-pmtu --set-mss value Explicitly set MSS option to specified value.
  • Page 33 Bugs? What's this? ;-) Well... the counters are not reliable on sparc64. COMPATIBILITY WITH IPCHAINS This iptables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only traversed for packets coming into the local host and originating from the local host respectively.

  • Page 34: See Also

    Rusty Russell wrote iptables, in early consultation with Michael Neuling. Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic packet selection framework in iptables, then wrote the mangle table, the owner match, the mark stuff, and ran around doing cool stuff everywhere.
  • Page 35 Manpage of IPTABLES Index NAME SYNOPSIS DESCRIPTION TARGETS TABLES OPTIONS COMMANDS PARAMETERS OTHER OPTIONS MATCH EXTENSIONS icmp limit multiport mark owner state conntrack dscp pkttype length unclean TARGET EXTENSIONS MARK REJECT http://www.iptablesrocks.org/syntax/man_iptables.htm (19 of 20) [2/13/2004 8:04:51 PM]...
  • Page 36 Manpage of IPTABLES MIRROR SNAT DNAT MASQUERADE REDIRECT ULOG TCPMSS DSCP DIAGNOSTICS BUGS COMPATIBILITY WITH IPCHAINS SEE ALSO AUTHORS This document was created by man2html, using the manual pages. Time: 05:21:18 GMT, January 07, 2004 http://www.iptablesrocks.org/syntax/man_iptables.htm (20 of 20) [2/13/2004 8:04:51 PM]...
  • Page 37 When running a typical web server, you need a firewall that is secure and offers protection, but you also need one that allows all needed traffic to be able to enter and leave the server so that your server's day to day operations can carry on unimpeded. This particular iptables configuration does the following: 1.
  • Page 38 Your kernel should now log the activity of the soon to be firewall to /var/log/firewall. Once we start up the iptables firewall, the /var/log/firewall file will be the location of the logging output of the firewall. This output will, in turn, be analyzed by the "Iptables Log Analyzer" tool and put in to a web accesible and user friendly format.
  • Page 39 iptablesrocks.org - Preparation Proceed to the next step home syntax & structure examples contact links Site last modified: February 13, 2004 15:27:51 http://www.iptablesrocks.org/guide/preparation.php (2 of 2) [2/13/2004 8:04:52 PM]...
  • Page 40 < /root/firewall_reset If you don't get an error, the script worked. The last thing you will want to do is to actually look at the iptables status just to make sure that your server is completely open as it should be. The following command will display your current iptables status:...
  • Page 41 That's it. Now save and exit out of the crontab editor. That's it. Until the crontab is disabled, your server's iptables ruleset will reset every 15 minutes. This means that if you lock yourself out later on in this setup guide, you'll only have to wait a maximum of 15 minutes before the firewall resets and the erroneous rules are dropped.
  • Page 42 Deploying the firewall: Well, it's finally time to create the main firewall ruleset script. We will simply create an importable iptables ruleset script and then import it into the iptables ruleset on your server. As soon as we import it, it instantly becomes active. So let's get started.
  • Page 43 Now import the firewall into your server's iptables ruleset... iptables-restore < /root/primary_firewall If you don't get any errors, your firewall should now be active. So let's take a look at the iptables status and see what it looks like. iptables -L...
  • Page 44 LOG_DROP all -- anywhere anywhere Chain LOG_ACCEPT (2 references) target prot opt source destination LOG all -- anywhere anywhere LOG level warning tcp-options ip-options prefix `[IPTABLES ACCEPT] : ' ACCEPT all -- anywhere anywhere Chain LOG_DROP (2 references) target prot opt source destination...
  • Page 45 iptablesrocks.org - Deploying the firewall Important Note: Now that your firewall is up and running, you will want to disable the "safetynet" crontab so that your firewall will remain up and running. Proceed to the next step home syntax & structure examples contact links...
  • Page 46 "insmod ip_conntrack_ftp". OK, assuming all your tests went smoothly your firewall should be in good shape. In the next step, we'll install the "Iptables Log Analyzer" package which will allow you to view your log entries in a nice web based environment.
  • Page 47 Installing Iptables Log Analyzer: Iptables Log Analyzer is a package that analyzes the log output from your iptables firewall, stores the info in a database and then produces a nice user friendly web interface from where you can monitor your firewall log output at any time. The interface even lets you sort throught the logs and group logs by category.
  • Page 48 - Iptables Log Analyzer # Host of the MySQL database $db_host="localhost"; # User of the MySQL database $db_user="iptables_user"; # Password of the MySQL database #Make sure you enter your "iptables_user" password in place of the red x's below $db_password="xxxxxx";...
  • Page 49 Open a browser and go to: http://www.yourdomain.com/firewall You should get the Iptables Log Analyzer screen. It's pretty self explanatory, so just play around with it for a while and you'll figure it out. If you don't see any logs yet, you can trigger a test by logging out of your server and then logging in again via SSH. The SSH connection will be recorded in the iptables logs and this will appear on the Iptables Log Analyzer screen.