作 者 | 土豆居士 微信公众号 | 一口Linux iptables的结构： iptables由上而下，由Tables，Chains，Rules组成。 一、iptables的表tables与链chains iptables有Filter, NAT, Mangle, Raw四种内建表： 1. Filter表 Filter是iptables的默认表，它有以下三种内建链 (chains)： ...

iptables：用来管理 Linux 防火墙的命令程序，位于 /sbin/iptables 目录下，属于 用户空间 的防火墙管理体系。 netfilter：Linux 内核中实现包过滤防火墙的内部结构，一般 不以程序 或 文件 的形式存在，属于 内核空间 的防火墙管理体系。

Since iptables is a kernel function, you’re not going to see processes running so no ps command is going to tell you anything about whether or how it is working. You can, however, easily check ...

Mastering iptables could take a while, but if you have a few rules to cover the basic security needs, you'll be well on your way to protecting your Linux system. Jack Wallen explains some key ...

Linux's iptables allows powerful firewalls to be implemented at a minute fraction of the cost of many commercial offerings. Basic iptables firewalls are packet filters, which means they inspect the ...

Most of us think of iptables strictly as a firewall tool for keeping remote attackers at bay. But did you know it also can be used to keep local users in line? The experimental match extension owner ...

Netfilter, Linux's in-kernel "packet mangling" infrastructure, and iptables, the administrative tool that manages it, represent a substantial improvement over ipchains, the previous option ...

How to Block Multiple IP Addresses on IPTables. When you use IPTables to create a firewall for your company's Web server, one way to prevent certain users from accessing the server is to block ...

You can use iptables-save and iptables-restore to generate and load one, but it's just as easy to make an /etc/rc.d/rc.firewall script and link it in at the beginning of the /etc/rc.d/rc.inet* chain.

The iptables -L command, by the way, doesn't really show enough info to be useful for troubleshooting. We'd need to see the actual script you're running, at least the parts relevant to SMTP.