iptables 命令和 iptables.service 服务有什么关系 ?

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关于iptables 命令和 iptabls.service 的一些疑惑
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我对 iptables 命令和 iptabls.service 的一些疑惑,在 unix.stackexchange.com 提了相关问题，有小伙伴为我做了解答，下面为问题和答案

我一直以为因为有 iptables.service 服务才可以使用 iptables 命令，实际上并不是这样的，iptalbes 是基于内核的，和 iptables.service 没有关系，不用安装任何工具包就可以使用 iptable 命令添加的防火墙规则，只是添加的规则是临时的，基于内存的，会在系统重启前消失，所以需要 iptables.service,firewalld.service 来对添加的规则进行保存。在系统重启后重载对应的防火墙规则，在系统关机时卸载对应的规则。

问题：

What is the difference between the iptables command and iptables.service?

I always thought I could only use the iptables command if I had the iptables.service service installed, but then I found out I was wrong

┌──[root@vms16.liruilongs.github.io]-[~]
└─$systemctl status iptables.service
Unit iptables.service could not be found.
┌──[root@vms16.liruilongs.github.io]-[~]
└─$iptables -A INPUT -p icmp --icmp-type 13 -j DROP
┌──[root@vms16.liruilongs.github.io]-[~]
└─$iptables -A OUTPUT -p icmp --icmp-type 14 -j DROP

After adding the rule, it took effect immediately

Without the iptables.service service, the command can still be used

┌──[root@vms16.liruilongs.github.io]-[~]
└─$whereis iptables
iptables: /usr/sbin/iptables /usr/libexec/iptables /usr/share/man/man8/iptables.8.gz
┌──[root@vms16.liruilongs.github.io]-[~]
└─$which iptables
/usr/sbin/iptables

I’m curious why we need iptables.service and what it means, for simplicity we can use firewalld.service.

┌──[root@vms16.liruilongs.github.io]-[~]
└─$yum -y install  iptables-services.x86_64 > /dev/null
┌──[root@vms16.liruilongs.github.io]-[~]
└─$systemctl status iptables.service
● iptables.service - IPv4 firewall with iptables
   Loaded: loaded (/usr/lib/systemd/system/iptables.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

I installed it and found only the configuration file

┌──[root@vms16.liruilongs.github.io]-[~]
└─$rpm -qlc iptables
/etc/sysconfig/ip6tables-config
/etc/sysconfig/iptables-config

What else does iptable.service do?

Can I assume so? iptables is kernel related and does not require iptables.service to be installed to work, but I see a lot of people reloading configuration files and restarting iptable.service after changing iptable rules, is that the right idea?

答案：

The iptables command is used to add or delete rules and chains and can be used without the service file. What iptables.service does is to automatically load a saved ruleset on boot and to unload the rules at shutdown. There’s a few safety checks in the scripts, like setting default chain policies to ACCEPT on shutdown, to prevent the system from having unusable rulesets. If you want to manually load rules every time you boot the system you can, the service just makes it easier.

firewalld presents a simpler interface to defining rules than iptables but that is really the major difference. And underneath the covers, firewalld uses iptables to implement the rules. Personally, I prefer using iptables but I have gotten used to the configuration over the years. The choice of iptables or firewalld is really up to what you’re comfortable with.

Thank you very much, it solved my doubts. Am I to understand that the rules configured with iptables are temporary, in-memory behavior (like /proc), not persistent, and if the system is rebooted, the rules are gone unless you export the data before shutting down. iptables.service automatically saves these rules and loads them automatically after a reboot. @doneal24 –
山河以无恙

@山河以无恙 Your understanding is correct. Any changes made by the iptables command will disappear when you reboot unless you save them and then reload after the boot. –
doneal24

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