iptables is the userspace command line tool used to configure the packet filtering engine in the Linux kernel.
Download, build and install:
wget http://www.netfilter.org/projects/iptables/files/iptables-1.4.21.tar.bz2 tar -xjf iptables-1.4.21.tar.bz2 cd iptables-1.4.21 ./configure --host=arm-linux-gnueabi --target=arm-linux-gnueabi --prefix= make make install DESTDIR=/home/export/rootfs
The link below contains a bzip2 tarball of iptables compiled for ARM: