User guide

Chapter 2. Securing Your Network
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• IPTABLES_STATUS_NUMERIC — Outputs IP addresses in numeric form instead of domain or
hostnames. This directive accepts the following values:
• yes — The default value. Returns only IP addresses within a status output.
• no — Returns domain or hostnames within a status output.
2.6.5. IPTables and IPv6
If the iptables-ipv6 package is installed, netfilter in Red Hat Enterprise Linux can filter the next-
generation IPv6 Internet protocol. The command used to manipulate the IPv6 netfilter is ip6tables.
Most directives for this command are identical to those used for iptables, except the nat table is
not yet supported. This means that it is not yet possible to perform IPv6 network address translation
tasks, such as masquerading and port forwarding.
Rules for ip6tables are saved in the /etc/sysconfig/ip6tables file. Previous rules saved by
the ip6tables initscripts are saved in the /etc/sysconfig/ip6tables.save file.
Configuration options for the ip6tables init script are stored in /etc/sysconfig/ip6tables-
config, and the names for each directive vary slightly from their iptables counterparts.
For example, the iptables-config directive IPTABLES_MODULES:the equivalent in the
ip6tables-config file is IP6TABLES_MODULES.
2.6.6. Additional Resources
Refer to the following sources for additional information on packet filtering with iptables.
• Section 2.5, “Firewalls” — Contains a chapter about the role of firewalls within an overall security
strategy as well as strategies for constructing firewall rules.
2.6.6.1. Installed IP Tables Documentation
• man iptables — Contains a description of iptables as well as a comprehensive list of targets,
options, and match extensions.
2.6.6.2. Useful IP Tables Websites
• http://www.netfilter.org/ — The home of the netfilter/iptables project. Contains assorted information
about iptables, including a FAQ addressing specific problems and various helpful guides by
Rusty Russell, the Linux IP firewall maintainer. The HOWTO documents on the site cover subjects
such as basic networking concepts, kernel packet filtering, and NAT configurations.
• http://www.linuxnewbie.org/nhf/Security/IPtables_Basics.html — An introduction to the way packets
move through the Linux kernel, plus an introduction to constructing basic iptables commands.