Beyond Linux® From Scratch (systemd Edition) - Version 9.0

Chapter 4. Security

Iptables-1.8.3

Introduction to Iptables

The next part of this chapter deals with firewalls. The principal firewall tool for Linux is Iptables. You will need to install Iptables if you intend on using any form of a firewall.

This package is known to build and work properly using an LFS-9.0 platform.

Package Information

Iptables Dependencies

Optional

nftables

User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/iptables

Kernel Configuration

A firewall in Linux is accomplished through a portion of the kernel called netfilter. The interface to netfilter is Iptables. To use it, the appropriate kernel configuration parameters are found in: 

[*] Networking support  --->                                    [CONFIG_NET]
      Networking Options  --->
        [*] Network packet filtering framework (Netfilter) ---> [CONFIG_NETFILTER]

Installation of Iptables

[Note]

Note

The installation below does not include building some specialized extension libraries which require the raw headers in the Linux source code. If you wish to build the additional extensions (if you aren't sure, then you probably don't), you can look at the INSTALL file to see an example of how to change the KERNEL_DIR= parameter to point at the Linux source code. Note that if you upgrade the kernel version, you may also need to recompile Iptables and that the BLFS team has not tested using the raw kernel headers.

For some non-x86 architectures, the raw kernel headers may be required. In that case, modify the KERNEL_DIR= parameter to point at the Linux source code.

Install Iptables by running the following commands: 

./configure --prefix=/usr      \
            --sbindir=/sbin    \
            --disable-nftables \
            --enable-libipq    \
            --with-xtlibdir=/lib/xtables &&
make

This package does not come with a test suite.

Now, as the root user: 

make install &&
ln -sfv ../../sbin/xtables-legacy-multi /usr/bin/iptables-xml &&

for file in ip4tc ip6tc ipq iptc xtables
do
  mv -v /usr/lib/lib${file}.so.* /lib &&
  ln -sfv ../../lib/$(readlink /usr/lib/lib${file}.so) /usr/lib/lib${file}.so
done

Command Explanations

--disable-nftables: This switch disables building nftables compat. Omit this switch if you have installed nftables.

--enable-libipq: This switch enables building of libipq.so which can be used by some packages outside of BLFS.

--with-xtlibdir=/lib/xtables: Ensure all Iptables modules are installed in the /lib/xtables directory.

--enable-nfsynproxy: This switch enables installation of nfsynproxy SYNPROXY configuration tool.

ln -sfv ../../sbin/xtables-legacy-multi /usr/bin/iptables-xml: Ensure the symbolic link for iptables-xml is relative.

Configuring Iptables

Introductory instructions for configuring your firewall are presented in the next section: Firewalling

Systemd Unit

To set up the iptables firewall at boot, install the iptables.service unit included in the blfs-systemd-units-20180105 package. 

make install-iptables

Contents

Installed Programs: ip6tables, ip6tables-restore, ip6tables-save, iptables, iptables-restore, iptables-save, iptables-xml, nfsynproxy (optional) and xtables-multi
Installed Libraries: libip4tc.so, libip6tc.so, libipq.so, libiptc.so, and libxtables.so
Installed Directories: /lib/xtables and /usr/include/libiptc

Short Descriptions

iptables

is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel.

iptables-restore

is used to restore IP Tables from data specified on STDIN. Use I/O redirection provided by your shell to read from a file.

iptables-save

is used to dump the contents of an IP Table in easily parseable format to STDOUT. Use I/O-redirection provided by your shell to write to a file.

iptables-xml

is used to convert the output of iptables-save to an XML format. Using the iptables.xslt stylesheet converts the XML back to the format of iptables-restore.

ip6tables*

are a set of commands for IPV6 that parallel the iptables commands above.

nfsynproxy

(optional) configuration tool. SYNPROXY target makes handling of large SYN floods possible without the large performance penalties imposed by the connection tracking in such cases.

xtables-multi

is a binary that behaves according to the name it is called by.

Last updated on 2019-08-18 18:01:59 -0700