linux设置iptables防火墙的详细步骤(centos防火墙设置方法)
<p style='margin: 0px; padding: 5px 0px; outline: none; font-size: 14px; line-height: 30px; font-family: tahoma, arial, "Microsoft YaHei";'>我们 来讨论一下如何为你的CentOS 服务器来设置简单的防火墙。 这里我们以DigitalOcean的CentOS 6 VPS为基础来讨论的，同样也适用于 阿里云上其他类型的LINUX系统。 （阿里云有个云盾系统，因此在你自己的VPS上不设置防火墙也是可以的）</p>
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需要说明的是： 本文只涉及最基础最常用的防火墙设置，能屏蔽一些常用的攻击，但并不能彻底保证你的服务器的安全。</p>
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系统的随时更新 以及 关闭不必要的服务 仍然是保证系统安全非常重要的步骤。</p>
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如果你需要更全面的了解iptables，阅读本文后，请google或是阅读更加深入的资料!</p>
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首先简单介绍一下什么是IPTables:</p>
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iptables是Linux内核中内置的防火墙，可以允许管理员通过设置table, chain以及相关的规则来进行数据包过滤和NAT。 一般来讲，iptables防火墙已经内置于CentOS 6及其他Linux版本中，而且iptables服务默认都是启动的。 iptables应用于IPv4, 如果要用IPv6，需要使用ip6tables.</p>
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iptables的命令格式：</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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iptables[-ttable]command[-jtarget]</div>
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[-ttable]：用来指明使用的表，有三种选项:filter,nat和mangle，如果未指定，则使用filter作为缺省表。事实上，对于单个服务器的防火墙配置，一般来讲，我们只需要对filter表进行配件就OK了。filter表包括INPUT,OUTPUT,和FORWARD三个chain.</p>
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command表明iptables命名要做什么，比如</p>
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-A（–append):该命令会把一条规则附件到chain的末尾。</p>
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-D（–delete)用来删除某个规则。</p>
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-F（–flush)如果指定了chain,删除该chain中的所有规则，如果未指定chain,则删除所有chain中的所有规则。</p>
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target:是由规则指定的操作。包括下面几种：</p>
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ACCEPT:接收信息包(允许它前往目的地），并且将停止遍历chain.</p>
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DROP：拒绝，</p>
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此外还有REJECT,RETURN,LOG,REDIRECT,MARK,MIRROR,MAQUERADE等。</p>
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具体的iptables的语法和概念就不再多说了，请参照iptablesmanpage官方文档.</p>
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简单来说，iptables防火墙是由一系列的规则(rule)组成，一个数据请求进来，会依次和这些规则进行比较，如果正好符合规则的定义，那这个数据请求要么会被接收ACCEPT，要么被拒绝DRIP。如果不符合任何规则的定义，最后缺省的规则会被应用。</p>
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开始操作之前：</p>
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注意：一定要把你在DigitalOcean/Linode/阿里云上的服务器做一下快照备份，否则一旦你iptables的配置出了问题，极有可能把你自己挡在门外，你自己都无法连接到服务器了！！出现这种情况可是会欲哭无泪呀，除了重新做系统好像没有更好的办法了。（DigitalOcean提供了一个webconsole的界面，有时候会给你反悔和擦除iptables设置的机会，但阿里云没有）</p>
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决定哪些端口需要开放</p>
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首先，SSH的端口22自然是需要开放的，否则我们就无法登录服务器了。</p>
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一般来讲，CentOS的VPS经常作为用LAMP搭建的Web服务器，FTP服务器，Mail服务器等。</p>
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对于Web服务来说，需要开放80端口，如果是HTTPS/SSL协议的话，还需用开放443端口</p>
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对于Mail服务来说，由于涉及SMTP,POP3,IMAP协议，需要开放的端口如下：</p>
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SMTP:25SecureSMTP:465POP3:110SecurePOP3:995IMAP:143IMAPoverSSL:993</p>
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对于FTP服务来说，需要开放20,21两个端口</p>
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第一步：屏蔽最常见的攻击</p>
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缺省情况下，CentOS的iptables的设置是允许任何数据通过的。</p>
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我们首先要清空iptables中的所有的规则：</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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iptables-F</div>
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然后我们加上阻止简单扫描和攻击的规则</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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iptables-AINPUT-ptcp--tcp-flagsALLNONE-jDROP#NONE包(所有标识bit都没有设置)主要是扫描类的数据包<br>
iptables-AINPUT-ptcp!--syn-mstate--stateNEW-jDROP#防止sync-flood攻击<br>
iptables-AINPUT-ptcp--tcp-flagsALLALL-jDROP#ALL包（所有的标注bit都被设置了）也是网络扫描的数据包</div>
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关于sync-flood,请参照wikipedia的解释。</p>
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第二步：为相应的服务开放对应的端口</p>
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首先我们应该接受本机localhost的任何请求，否则，数据库连接等将无法工作</p>
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1<br>
iptables-AINPUT-ilo-jACCEPT<br>
对于不同的服务需要开放不同的端口</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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iptables-AINPUT-ptcp--dport22-jACCEPT#SSH<br>
iptables-AINPUT-ptcp--dport80-jACCEPT#HTTP<br>
iptables-AINPUT-ptcp--dport443-jACCEPT#HTTPS<br>
iptables-AINPUT-ptcp--dport25-jACCEPT#SMTP<br>
iptables-AINPUT-ptcp--dport465-jACCEPT#SecureSMTP<br>
iptables-AINPUT-ptcp--dport110-jACCEPT#POP3<br>
iptables-AINPUT-ptcp--dport995-jACCEPT#SecurePOP3<br>
iptables-AINPUT-ptcp--dport143-jACCEPT#IMAP<br>
iptables-AINPUT-ptcp--dport993-jACCEPT#SecureIMAP</div>
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第三步：加上通用的规则</p>
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首先要允许所有从服务器端发起的连接，由此返回的响应数据应该是允许的！比如VPS发起的yumupdate,必须要允许外部的update数据进来</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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iptables-IINPUT-mstate--stateESTABLISHED,RELATED-jACCEPT</div>
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最后，设置缺省的策略：屏蔽任何进入的数据请求，允许所有从Server发出的请求</p>
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<p>
代码如下:</p>
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iptables-POUTPUTACCEPT</p> <p>iptables-PINPUTDROP</div>
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至此，规则设置完毕</p>
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第四步：保存设置</p>
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首先通过下面的命令查看一下我们的设置是否正确！</p>
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<p>
代码如下:</p>
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iptable-L-n</div>
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确认没有问题后，执行下面的命令</p>
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<span><u>复制代码</u></span>
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<p>
代码如下:</p>
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serviceiptablessave</div>
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执行上述命令后，相应的规则会写入/etc/sysconfig/iptables这个文件，你可以检查一下看看。</p>
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最后执行</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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serviceiptablesrestart.</div>
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重新启动iptables防火墙，以使上述设置生效。</p>
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最佳的方法：</p>
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为了更方便的修改和维护自己的iptables的设置，我一般是把所有的iptables的设置先写到一个单独文件中，测试没有问题后。然后再保存到iptable的配置文件中。</p>
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下面是我自己的iptables文件~/script/firewall.sh</p>
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<span><u>复制代码</u></span>
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代码如下:</p>
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#!/bin/bash<br>
#Asimpleiptablesfirewallconfiguration</p> <p>PATH=/sbin:/bin:/usr/sbin:/usr/bin;exportPATH</p> <p>#flush/eraseoriginalrules<br>
iptables-F#清除所有已制定的rule<br>
iptables-X#清除用户自定义的chain/table<br>
iptables-Z#将所有的chain的计数和流量统计归零</p> <p>#Acceptlocalhostconnetting,nomatterwhatitis<br>
iptables-AINPUT-ilo-jACCEPT</p> <p>#Acceptanyresponsepackagewhichisinitiatedfrominside<br>
iptables-AINPUT-mstate--stateESTABLISHED,RELATED-jACCEPT</p> <p>#blockmostcommonnetworkattacks(reconpacketsandsyn-floodattack)<br>
iptables-AINPUT-ptcp--tcp-flagsALLNONE-jDROP<br>
iptables-AINPUT-ptcp!--syn-mstate--stateNEW-jDROP<br>
iptables-AINPUT-ptcp--tcp-flagsALLALL-jDROP</p> <p>#openportsfordifferentservices<br>
iptables-AINPUT-ptcp--dport22-jACCEPT#SSH<br>
iptables-AINPUT-ptcp--dport80-jACCEPT#HTTP<br>
#iptables-AINPUT-ptcp--dport443-jACCEPT#HTTPS<br>
#iptables-AINPUT-ptcp--dport25-jACCEPT#SMTP<br>
#iptables-AINPUT-ptcp--dport465-jACCEPT#SecureSMTP<br>
#iptables-AINPUT-ptcp--dport110-jACCEPT#POP3<br>
#iptables-AINPUT-ptcp--dport995-jACCEPT#SecurePOP</p> <p>#ICMPconfiguration<br>
#TopreventICMPDDOS,wedonotallowICMPtype8(echo-request)orlimitthisrequestwith1/second<br>
#someICMPrequestsareallowed.<br>
icmp_type="0341112141618"<br>
forticmpin$icmp_type<br>
do<br>
iptables-AINPUT-picmp--icmp-type$ticmp-jACCEPT<br>
done<br>
#iptables-AINPUT-picmp--icmp-type8-mlimit--limit1/second-jACCEPT</p> <p>#defaultpolicies<br>
iptables-POUTPUTACCEPT<br>
iptables-PINPUTDROP</p> <p>#saveto/etc/sysconfig/iptables<br>
/etc/init.d/iptablessave</div>
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你可以根据你的需要进行相应的修改。</p>
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