规则链与策略:

规则:

ACCEPT：允许通过
LOG：记录日志
REJECT：拒绝通过，给出返回值
DROP：丢弃

规则链:

PREROUTING：路由前处理
INPUT：处理入站数据
OUTPUT：处理出站数据
FORWARD：处理转发数据
POSTROUTING：路由后处理
raw表：确定是否对数据包状态跟踪
mangle表：设置标记
nat表：修改数据包源、目标IP或端口
filter表：过滤

规则顺序

规则表先后顺序：raw表→mangle表→nat表→filter表
规则链先后顺序：
入站：PREROUTING→INPUT
出站：OUTPUT→POSTROUTING
转发：PREROUTING→FORWARD→POSTROUTING

基本参数：

iptables [-t 表名] 选项 [链名] [条件] [控制类型]

Usage: iptables -[ACD] chain rule-specification [options]
       iptables -I chain [rulenum] rule-specification [options]
       iptables -R chain rulenum rule-specification [options]
       iptables -D chain rulenum [options]
       iptables -[LS] [chain [rulenum]] [options]
       iptables -[FZ] [chain] [options]
       iptables -[NX] chain
       iptables -E old-chain-name new-chain-name
       iptables -P chain target [options]
       iptables -h (print this help information)

Commands:
Either long or short options are allowed.
  --append  -A chain            Append to chain
  --check   -C chain            Check for the existence of a rule
  --delete  -D chain            Delete matching rule from chain
  --delete  -D chain rulenum
                                Delete rule rulenum (1 = first) from chain
  --insert  -I chain [rulenum]
                                Insert in chain as rulenum (default 1=first)
  --replace -R chain rulenum
                                Replace rule rulenum (1 = first) in chain
  --list    -L [chain [rulenum]]
                                List the rules in a chain or all chains
  --list-rules -S [chain [rulenum]]
                                Print the rules in a chain or all chains
  --flush   -F [chain]          Delete all rules in  chain or all chains
  --zero    -Z [chain [rulenum]]
                                Zero counters in chain or all chains
  --new     -N chain            Create a new user-defined chain
  --delete-chain
            -X [chain]          Delete a user-defined chain
  --policy  -P chain target
                                Change policy on chain to target
  --rename-chain
            -E old-chain new-chain
                                Change chain name, (moving any references)
Options:
    --ipv4      -4              Nothing (line is ignored by ip6tables-restore)
    --ipv6      -6              Error (line is ignored by iptables-restore)
[!] --protocol  -p proto        protocol: by number or name, eg. `tcp'
[!] --source    -s address[/mask][...]
                                source specification
[!] --destination -d address[/mask][...]
                                destination specification
[!] --in-interface -i input name[+]
                                network interface name ([+] for wildcard)
 --jump -j target
                                target for rule (may load target extension)
  --goto      -g chain
                              jump to chain with no return
  --match       -m match
                                extended match (may load extension)
  --numeric     -n              numeric output of addresses and ports
[!] --out-interface -o output name[+]
                                network interface name ([+] for wildcard)
  --table       -t table        table to manipulate (default: `filter')
  --verbose     -v              verbose mode
  --wait        -w              wait for the xtables lock
  --line-numbers                print line numbers when listing
  --exact       -x              expand numbers (display exact values)
[!] --fragment  -f              match second or further fragments only
  --modprobe=<command>          try to insert modules using this command
  --set-counters PKTS BYTES     set the counter during insert/append
[!] --version   -V              print package version.

基本使用方法：

查看已有规则：

iptables -L

清空所有规则：

iptables -F

拒绝INPUT

iptables -P INPUT DROP

允许所有ping：

iptables -I INPUT -p icmp -j ACCEPT

在末尾加入允许未被其他规则匹配的数据包：

iptables -t filter -A INPUT -j -ACCEPT

删除INPUT第二条规则：

iptables -D INPUT 2

仅允许来自172.27.8.0/22的用户连接ssh服务

iptables -I INPUT -s 172.27.8.0/22 -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j REJECT

不允许任何用户访问本机3306端口

iptables -I INPUT -p tcp --dport 3306 -j REJECT
iptables -I INPUT -p udp --dport 3306 -j REJECT

拒绝其他用户通过网卡eth1访问本机http服务

iptables -I INPUT -i eth1 -p tcp --dport 80 -j REJECT

禁止用户访问www.baidu.com

iptables -I FORWARD -d www.baidu.com -j DROP

禁止172.27.8.22的用户上网

iptables -I FORWARD -s 172.27.8.22 -j DROP

流量均衡：

将访问流量分流至内网三台不同主机：

iptables -A PREROUTING -i eth1 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT -to-destination 172.27.8.10
iptables -A PREROUTING -i eth1 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT -to-destination 172.27.8.20
iptables -A PREROUTING -i eth1 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT -to-destination 172.27.8.30

使用上述操作，规则仅当前有效，如需重启依然有效，执行service iptables save 将规则写入/etc/sysconfig/iptables中
顺便再贴一个iptables配置：

# Generated by iptables-save v1.4.7 on Thu Apr 16 01:33:03 2015
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
#允许本机回环地址
-A INPUT -i lo -p all -j ACCEPT
##允许这些IP所有操作
-A INPUT -s 110.122.120.54/32 -j ACCEPT 
-A INPUT -s 110.122.120.98/32 -j ACCEPT
##允许DNS解析
-A INPUT -p udp --sport 53 -j ACCEPT
#允许5672端口访问
-A INPUT -s 10.10.2.160 -p tcp --sport 5672 -j ACCEPT
##禁止eth0上27017入站和出站
-A INPUT -i eth0  -p tcp --dport 27017 -j DROP
-A OUTPUT -o eth0 -p tcp --sport 27017 -j DROP
##允许zabbix的10050端口
-A INPUT -s 100.10.2.160 -p tcp --dport 10050 -j ACCEPT
##运许snmp的161端口
-A INPUT -s 100.10.2.160 -p tcp --dport 10050 -j ACCEPT
##允许程序主机访问指定IP的4506端口
-A INPUT -s 172.27.1.75 -p tcp --dport 4506 -j ACCEPT
##允许下列端口访问
-A INPUT -p tcp --dport 8080 -j ACCEPT
-A INPUT -p tcp --dport 8090 -j ACCEPT
-A INPUT -p tcp --dport 13000 -j ACCEPT
-A INPUT -p tcp --dport 9000 -j ACCEPT
-A INPUT -p tcp --dport 8888 -j ACCEPT
COMMIT