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iptables防火墙基本概念与基本语法_chain forward (policy drop)
作者：我家自动化 | 2024-05-27 12:16:30
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chain forward (policy drop)
一. 防火墙概述
防火墙由硬件防火墙，软件防火墙，软硬兼容等。防火墙一般部署在网络边缘，作用于过滤某些字符，IP，根据规则，执行：允许，拒绝，转发，丢弃等。防火墙根据其管理的范围右可以分为可以将其划分为主机防火墙和网络防火墙；根据其工作机制来区分又可分为包过滤型防火墙（netfilter）和代理服务器（Proxy）。
二. 包过滤防火墙 iptables
包过滤防火墙：包过滤防火墙过滤系统是一台路由器或是一台主机，可以根据过滤规则阻塞内部主机和外部主机或另外一个网络之间的连接。包过滤防火墙bai工作在网络协议ip层，它du只对ip包的源地址、目标地址及zhi相应端口进行处理，因此速度比较dao快，能够处理的并发连接比较多，缺点是对应用层的攻击无能为力。包过滤型防火墙主要依赖于Linux内核软件netfilter，它是一个Linux内核“安全框架”，而iptables是内核软件netfilter的配置工具，工作于用户空间。iptables/netfilter组合就是Linux平台下的过滤型防火墙，并且这个防火墙软件是免费的，可以用来替代商业防火墙软件，来完成网络数据包的过滤，修改，重定向以及网络地址转换（nat）等功能。
ps：在有些Linux发行版上，我们可以使用systemctl start iptables来启动iptables服务，但需要指出的是，iptables 并不是也不依赖于守护进程，它只是利用Linux内核提供的功能。
三. iptables四表
四表:filter,nat,mangle,raw，其中filter是默认表，表示优先处理级：raw>mangle>nat>filter
四表的作用：
filter：一般的过滤功能
nat:用于nat功能（端口映射，地址映射等）
mangle:用于对特定数据包的修改，TTL等
raw:有限级最高，设置raw时一般是为了不再让iptables做数据包的链接跟踪处理，提高性能
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RAW 表只使用在PREROUTING链和OUTPUT链上,因为优先级最高，从而可以对收到的数据包在连接跟踪前进行处理。一但用户使用了RAW表,在某个链 上,RAW表处理完后,将跳过NAT表和 ip_conntrack处理,即不再做地址转换和数据包的链接跟踪处理了.
RAW表可以应用在那些不需要做nat的情况下，以提高性能。如大量访问的web服务器，可以让80端口不再让iptables做数据包的链接跟踪处理，以提高用户的访问速度。
1. raw表规则
iptables -t raw -L
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[root@localhost iproute2]# iptables -t raw -L Chain PREROUTING (policy ACCEPT) target prot opt source destination PREROUTING_direct all -- anywhere anywhere PREROUTING_ZONES_SOURCE all -- anywhere anywhere PREROUTING_ZONES all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination OUTPUT_direct all -- anywhere anywhere Chain OUTPUT_direct (1 references) target prot opt source destination Chain PREROUTING_ZONES (1 references) target prot opt source destination PRE_public all -- anywhere anywhere [goto] PRE_public all -- anywhere anywhere [goto] Chain PREROUTING_ZONES_SOURCE (1 references) target prot opt source destination Chain PREROUTING_direct (1 references) target prot opt source destination Chain PRE_public (2 references) target prot opt source destination PRE_public_log all -- anywhere anywhere PRE_public_deny all -- anywhere anywhere PRE_public_allow all -- anywhere anywhere Chain PRE_public_allow (1 references) target prot opt source destination Chain PRE_public_deny (1 references) target prot opt source destination Chain PRE_public_log (1 references) target prot opt source destination [root@localhost iproute2]#
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2. mangle表规则
[root@localhost iproute2]# iptables -t mangle -L Chain PREROUTING (policy ACCEPT) target prot opt source destination PREROUTING_direct all -- anywhere anywhere PREROUTING_ZONES_SOURCE all -- anywhere anywhere PREROUTING_ZONES all -- anywhere anywhere Chain INPUT (policy ACCEPT) target prot opt source destination INPUT_direct all -- anywhere anywhere Chain FORWARD (policy ACCEPT) target prot opt source destination FORWARD_direct all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination OUTPUT_direct all -- anywhere anywhere Chain POSTROUTING (policy ACCEPT) target prot opt source destination POSTROUTING_direct all -- anywhere anywhere Chain FORWARD_direct (1 references) target prot opt source destination Chain INPUT_direct (1 references) target prot opt source destination Chain OUTPUT_direct (1 references) target prot opt source destination Chain POSTROUTING_direct (1 references) target prot opt source destination Chain PREROUTING_ZONES (1 references) target prot opt source destination PRE_public all -- anywhere anywhere [goto] PRE_public all -- anywhere anywhere [goto] Chain PREROUTING_ZONES_SOURCE (1 references) target prot opt source destination Chain PREROUTING_direct (1 references) target prot opt source destination Chain PRE_public (2 references) target prot opt source destination PRE_public_log all -- anywhere anywhere PRE_public_deny all -- anywhere anywhere PRE_public_allow all -- anywhere anywhere Chain PRE_public_allow (1 references) target prot opt source destination Chain PRE_public_deny (1 references) target prot opt source destination Chain PRE_public_log (1 references) target prot opt source destination
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3. nat表规则
[root@localhost iproute2]# iptables -t nat -L Chain PREROUTING (policy ACCEPT) target prot opt source destination PREROUTING_direct all -- anywhere anywhere PREROUTING_ZONES_SOURCE all -- anywhere anywhere PREROUTING_ZONES all -- anywhere anywhere DOCKER all -- anywhere anywhere ADDRTYPE match dst-type LOCAL Chain INPUT (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination OUTPUT_direct all -- anywhere anywhere DOCKER all -- anywhere !loopback/8 ADDRTYPE match dst-type LOCAL Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- 172.17.0.0/16 anywhere POSTROUTING_direct all -- anywhere anywhere POSTROUTING_ZONES_SOURCE all -- anywhere anywhere POSTROUTING_ZONES all -- anywhere anywhere Chain DOCKER (2 references) target prot opt source destination RETURN all -- anywhere anywhere Chain OUTPUT_direct (1 references) target prot opt source destination Chain POSTROUTING_ZONES (1 references) target prot opt source destination POST_public all -- anywhere anywhere [goto] POST_public all -- anywhere anywhere [goto] Chain POSTROUTING_ZONES_SOURCE (1 references) target prot opt source destination Chain POSTROUTING_direct (1 references) target prot opt source destination Chain POST_public (2 references) [root@localhost iproute2]# iptables -t nat -L Chain PREROUTING (policy ACCEPT) target prot opt source destination PREROUTING_direct all -- anywhere anywhere PREROUTING_ZONES_SOURCE all -- anywhere anywhere PREROUTING_ZONES all -- anywhere anywhere DOCKER all -- anywhere anywhere ADDRTYPE match dst-type LOCAL Chain INPUT (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination OUTPUT_direct all -- anywhere anywhere DOCKER all -- anywhere !loopback/8 ADDRTYPE match dst-type LOCAL Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- 172.17.0.0/16 anywhere POSTROUTING_direct all -- anywhere anywhere POSTROUTING_ZONES_SOURCE all -- anywhere anywhere POSTROUTING_ZONES all -- anywhere anywhere Chain DOCKER (2 references) target prot opt source destination RETURN all -- anywhere anywhere Chain OUTPUT_direct (1 references) target prot opt source destination Chain POSTROUTING_ZONES (1 references) target prot opt source destination POST_public all -- anywhere anywhere [goto] POST_public all -- anywhere anywhere [goto] Chain POSTROUTING_ZONES_SOURCE (1 references) target prot opt source destination Chain POSTROUTING_direct (1 references) target prot opt source destination Chain POST_public (2 references) target prot opt source destination POST_public_log all -- anywhere anywhere POST_public_deny all -- anywhere anywhere POST_public_allow all -- anywhere anywhere Chain POST_public_allow (1 references) target prot opt source destination Chain POST_public_deny (1 references) target prot opt source destination Chain POST_public_log (1 references) target prot opt source destination Chain PREROUTING_ZONES (1 references) target prot opt source destination PRE_public all -- anywhere anywhere [goto] PRE_public all -- anywhere anywhere [goto] Chain PREROUTING_ZONES_SOURCE (1 references) target prot opt source destination Chain PREROUTING_direct (1 references) target prot opt source destination Chain PRE_public (2 references) target prot opt source destination PRE_public_log all -- anywhere anywhere PRE_public_deny all -- anywhere anywhere PRE_public_allow all -- anywhere anywhere Chain PRE_public_allow (1 references) target prot opt source destination Chain PRE_public_deny (1 references) target prot opt source destination Chain PRE_public_log (1 references) target prot opt source destination
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4. filter表规则
[root@localhost iproute2]# iptables -t filter -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere INPUT_direct all -- anywhere anywhere INPUT_ZONES_SOURCE all -- anywhere anywhere INPUT_ZONES all -- anywhere anywhere DROP all -- anywhere anywhere ctstate INVALID REJECT all -- anywhere anywhere reject-with icmp-host-prohibited Chain FORWARD (policy DROP) target prot opt source destination DOCKER-USER all -- anywhere anywhere DOCKER-ISOLATION-STAGE-1 all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED DOCKER all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere FORWARD_direct all -- anywhere anywhere FORWARD_IN_ZONES_SOURCE all -- anywhere anywhere FORWARD_IN_ZONES all -- anywhere anywhere FORWARD_OUT_ZONES_SOURCE all -- anywhere anywhere FORWARD_OUT_ZONES all -- anywhere anywhere DROP all -- anywhere anywhere ctstate INVALID REJECT all -- anywhere anywhere reject-with icmp-host-prohibited Chain OUTPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere OUTPUT_direct all -- anywhere anywhere Chain DOCKER (1 references) target prot opt source destination Chain DOCKER-ISOLATION-STAGE-1 (1 references) target prot opt source destination DOCKER-ISOLATION-STAGE-2 all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-ISOLATION-STAGE-2 (1 references) target prot opt source destination DROP all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-USER (1 references) target prot opt source destination RETURN all -- anywhere anywhere Chain FORWARD_IN_ZONES (1 references) target prot opt source destination FWDI_public all -- anywhere anywhere [goto] FWDI_public all -- anywhere anywhere [goto] Chain FORWARD_IN_ZONES_SOURCE (1 references) target prot opt source destination Chain FORWARD_OUT_ZONES (1 references) target prot opt source destination FWDO_public all -- anywhere anywhere [goto] FWDO_public all -- anywhere anywhere [goto] Chain FORWARD_OUT_ZONES_SOURCE (1 references) target prot opt source destination Chain FORWARD_direct (1 references) target prot opt source destination Chain FWDI_public (2 references) target prot opt source destination FWDI_public_log all -- anywhere anywhere FWDI_public_deny all -- anywhere anywhere FWDI_public_allow all -- anywhere anywhere ACCEPT icmp -- anywhere anywhere Chain FWDI_public_allow (1 references) target prot opt source destination Chain FWDI_public_deny (1 references) target prot opt source destination Chain FWDI_public_log (1 references) target prot opt source destination Chain FWDO_public (2 references) target prot opt source destination FWDO_public_log all -- anywhere anywhere FWDO_public_deny all -- anywhere anywhere FWDO_public_allow all -- anywhere anywhere Chain FWDO_public_allow (1 references) [root@localhost iproute2]# iptables -t filter -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere INPUT_direct all -- anywhere anywhere INPUT_ZONES_SOURCE all -- anywhere anywhere INPUT_ZONES all -- anywhere anywhere DROP all -- anywhere anywhere ctstate INVALID REJECT all -- anywhere anywhere reject-with icmp-host-prohibited Chain FORWARD (policy DROP) target prot opt source destination DOCKER-USER all -- anywhere anywhere DOCKER-ISOLATION-STAGE-1 all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED DOCKER all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere FORWARD_direct all -- anywhere anywhere FORWARD_IN_ZONES_SOURCE all -- anywhere anywhere FORWARD_IN_ZONES all -- anywhere anywhere FORWARD_OUT_ZONES_SOURCE all -- anywhere anywhere FORWARD_OUT_ZONES all -- anywhere anywhere DROP all -- anywhere anywhere ctstate INVALID REJECT all -- anywhere anywhere reject-with icmp-host-prohibited Chain OUTPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere OUTPUT_direct all -- anywhere anywhere Chain DOCKER (1 references) target prot opt source destination Chain DOCKER-ISOLATION-STAGE-1 (1 references) target prot opt source destination DOCKER-ISOLATION-STAGE-2 all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-ISOLATION-STAGE-2 (1 references) target prot opt source destination DROP all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-USER (1 references) target prot opt source destination RETURN all -- anywhere anywhere Chain FORWARD_IN_ZONES (1 references) target prot opt source destination FWDI_public all -- anywhere anywhere [goto] FWDI_public all -- anywhere anywhere [goto] Chain FORWARD_IN_ZONES_SOURCE (1 references) target prot opt source destination Chain FORWARD_OUT_ZONES (1 references) target prot opt source destination FWDO_public all -- anywhere anywhere [goto] FWDO_public all -- anywhere anywhere [goto] Chain FORWARD_OUT_ZONES_SOURCE (1 references) target prot opt source destination Chain FORWARD_direct (1 references) target prot opt source destination Chain FWDI_public (2 references) target prot opt source destination FWDI_public_log all -- anywhere anywhere FWDI_public_deny all -- anywhere anywhere FWDI_public_allow all -- anywhere anywhere ACCEPT icmp -- anywhere anywhere Chain FWDI_public_allow (1 references) target prot opt source destination Chain FWDI_public_deny (1 references) target prot opt source destination Chain FWDI_public_log (1 references) target prot opt source destination Chain FWDO_public (2 references) target prot opt source destination FWDO_public_log all -- anywhere anywhere FWDO_public_deny all -- anywhere anywhere FWDO_public_allow all -- anywhere anywhere Chain FWDO_public_allow (1 references) target prot opt source destination Chain FWDO_public_deny (1 references) target prot opt source destination Chain FWDO_public_log (1 references) target prot opt source destination Chain INPUT_ZONES (1 references) target prot opt source destination IN_public all -- anywhere anywhere [goto] IN_public all -- anywhere anywhere [goto] Chain INPUT_ZONES_SOURCE (1 references) target prot opt source destination Chain INPUT_direct (1 references) target prot opt source destination Chain IN_public (2 references) target prot opt source destination IN_public_log all -- anywhere anywhere IN_public_deny all -- anywhere anywhere IN_public_allow all -- anywhere anywhere ACCEPT icmp -- anywhere anywhere Chain IN_public_allow (1 references) target prot opt source destination ACCEPT tcp -- anywhere anywhere tcp dpt:ssh ctstate NEW,UNTRACKED ACCEPT tcp -- anywhere anywhere tcp dpt:http ctstate NEW,UNTRACKED Chain IN_public_deny (1 references) target prot opt source destination Chain IN_public_log (1 references) target prot opt source destination Chain OUTPUT_direct (1 references) target prot opt source destination
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四. iptables五链
5个链：PREROUTING,INPUT,FORWARD,OUTPUT,POSTROUTING。
PREROUTING:数据包进入路由表之前------(对数据包作路由选择前应用此链中的规则,所有的数据包进来的时侯都先由这个链处理）
INPUT:通过路由表后目的地为本机------(进来的数据包应用此规则链中的策略)
FORWARD:通过路由表后，目的地不为本机------(转发数据包时应用此规则链中的策略)
OUTPUT:由本机产生，向外转发------(外出的数据包应用此规则链中的策略)
POSTROUTIONG:发送到网卡接口之前------(对数据包作路由选择后应用此链中的规则,所有的数据包出来的时侯都先由这个链处理）
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nat 表的 PREROUTING 链
[root@localhost iproute2]# iptables -t nat -L PREROUTING
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
PREROUTING_direct all -- anywhere anywhere
PREROUTING_ZONES_SOURCE all -- anywhere anywhere
PREROUTING_ZONES all -- anywhere anywhere
DOCKER all -- anywhere anywhere ADDRTYPE match dst-type LOCAL
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每个链所对应表的规则
| 链 | 表 |
|---|---|
| PREROUTING | raw, mangle, nat |
| FORWARD | mangle, filter |
| INPUT | mangle, filter, nat |
| OUTPUT | raw, mangle, filter, nat |
| POSTROUTING | mangle, nat |
在实际使用iptables配置规则时，我们往往是以“表”为入口制定“规则”，所以我们将“链表”关系转化成“表链”关系：
| 表 | 链 |
|---|---|
| raw | PREROUTING，OUTPUT |
| mangle | PREROUTING，FORWARD，INPUT，OUTPUT，POSTROUTING |
| filter | FORWARD，INPUT，OUTPUT |
| nat | PREROUTING，INPUT，POSTROUTING |
按照表优先级
raw>mangle>nat>filter 通过
设置iptables规则时需要考量的要点：
-
根据要实现哪种功能，判断添加在那张“表”上
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根据报文流经的路径，判断添加在那个“链”上
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到本主机某进程的报文：PreRouting -> Input -> Process -> Output -> PostRouting
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由本主机转发的报文：PreRouting -> Forward -> PostRouting
对于每一条“链”上其“规则”的匹配顺序，排列好检查顺序能有效的提高性能，因此隐含一定的法则：
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同类规则（访问同一应用），匹配范围小的放上面
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不同类规则（访问不同应用），匹配到报文频率大的放上面
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将那些可由一条规则描述的多个规则合并为一个
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设置默认策略
同时，也一定要注意，在远程连接主机配置防火墙时注意：
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不要把“链”的默认策略修改为拒绝，因为有可能配置失败或者清除所有策略后无法远程到服务器，而是尽量使用规则条目配置默认策略
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为防止配置失误策略把自己也拒掉，可在配置策略时设置计划任务定时清除策略，当确定无误后，关闭该计划任务
iptables语法
iptables(选项)(参数)
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选项：
# 通用匹配：源地址目标地址的匹配 -p：指定要匹配的数据包协议类型； -s, --source [!] address[/mask] ：把指定的一个／一组地址作为源地址，按此规则进行过滤。当后面没有 mask 时，address 是一个地址，比如：192.168.1.1；当 mask 指定时，可以表示一组范围内的地址，比如：192.168.1.0/255.255.255.0。 -d, --destination [!] address[/mask] ：地址格式同上，但这里是指定地址为目的地址，按此进行过滤。 -i, --in-interface [!] <网络接口name> ：指定数据包的来自来自网络接口，比如最常见的 eth0 。注意：它只对 INPUT，FORWARD，PREROUTING 这三个链起作用。如果没有指定此选项， 说明可以来自任何一个网络接口。同前面类似，"!" 表示取反。 -o, --out-interface [!] <网络接口name> ：指定数据包出去的网络接口。只对 OUTPUT，FORWARD，POSTROUTING 三个链起作用。 # 查看管理命令 -L, --list [chain] 列出链 chain 上面的所有规则，如果没有指定链，列出表上所有链的所有规则。 # 规则管理命令 -A, --append chain rule-specification 在指定链 chain 的末尾插入指定的规则，也就是说，这条规则会被放到最后，最后才会被执行。规则是由后面的匹配来指定。 -I, --insert chain [rulenum] rule-specification 在链 chain 中的指定位置插入一条或多条规则。如果指定的规则号是1，则在链的头部插入。这也是默认的情况，如果没有指定规则号。 -D, --delete chain rule-specification -D, --delete chain rulenum 在指定的链 chain 中删除一个或多个指定规则。 -R num：Replays替换/修改第几条规则 # 链管理命令（这都是立即生效的） -P, --policy chain target ：为指定的链 chain 设置策略 target。注意，只有内置的链才允许有策略，用户自定义的是不允许的。 -F, --flush [chain] 清空指定链 chain 上面的所有规则。如果没有指定链，清空该表上所有链的所有规则。 -N, --new-chain chain 用指定的名字创建一个新的链。 -X, --delete-chain [chain] ：删除指定的链，这个链必须没有被其它任何规则引用，而且这条上必须没有任何规则。如果没有指定链名，则会删除该表中所有非内置的链。 -E, --rename-chain old-chain new-chain ：用指定的新名字去重命名指定的链。这并不会对链内部照成任何影响。 -Z, --zero [chain] ：把指定链，或者表中的所有链上的所有计数器清零。 -j, --jump target <指定目标> ：即满足某条件时该执行什么样的动作。target 可以是内置的目标，比如 ACCEPT，也可以是用户自定义的链。 -h：显示帮助信息；
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参数
| 参数 | 作用 |
|---|---|
| -p | 设置默认策略:iptables -P INPUT (DROP) |
| -F | 清空规则链 |
| -L | 查看规则链 |
| -A | 在规则链的末尾加入新规则 |
| -I | num 在规则链的头部加入新规则 |
| -D | num 删除某一条规则 |
| -s | 匹配来源地址IP/MASK，加叹号”!“表示除这个IP外 |
| -D | 匹配目标地址 |
| -i | 网卡名称 匹配从这块网卡流入的数据 |
| -o | 网卡名称 匹配从这块网卡流出的数据 |
| -p | 匹配协议,如tcp,udp,icmp |
| –dport num | 匹配目标端口号 |
| –sport num | 匹配来源端口号 |
命令选项输入顺序：
iptables -t 表名 <-A/I/D/R> 规则链名 [规则号] <-i/o 网卡名> -p 协议名 <-s 源IP/源子网> --sport 源端口 <-d 目标IP/目标子网> --dport 目标端口 -j 动作
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