默认情况下，RHEL 7 使用 FirewallD 服务来提供网络安全。
使用 iptables 服务时必须停止并禁用 FirewallD：

# systemctl stop firewalld.service
# systemctl disable firewalld.service

# systemctl enable iptables.service
# systemctl start iptables.service

iptables 服务现在由一个名为 iptables-services 的单独包提供：

# yum info iptables-services
Name        : iptables-services
Arch        : x86_64
Version     : 1.4.21
Release     : 13.el7
Size        : 23 k
Repo        : installed
From repo   : anaconda
Summary     : iptables and ip6tables services for iptables
URL         : http://www.netfilter.org/
License     : GPLv2
Description : iptables services for IPv4 and IPv6
            : 
            : This package provides the services iptables and ip6tables that have been split 
            : out of the base package since they are not active by default anymore.
这个包提供了 iptables 和 ip6tables 服务，这些服务已经从基础包中分离出来，因为它们在默认情况下不再处于活动状态。

iptables-services 包可能需要先安装：

# systemctl -a|grep iptables
● iptables.service                      not-found inactive dead      iptables.service

首先停止并禁用 firewalld 服务。

# systemctl stop firewalld.service
# systemctl disable firewalld.service
Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.
Removed symlink /etc/systemd/system/basic.target.wants/firewalld.service.

如果我们尝试启用 iptables 服务，它将失败。

# systemctl enable iptables.service
Failed to execute operation: No such file or directory

安装 iptables-services 包。

# yum install iptables-services -y

启用 iptables 服务：

# systemctl enable iptables.service
Created symlink from /etc/systemd/system/basic.target.wants/iptables.service to /usr/lib/systemd/system/iptables.service.

启动 iptables 服务：

# systemctl start iptables.service
#