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41.2. iptables - administration tools for packet filtering and NAT

Linux Iptables Manual

	
      Incoming
       Traffic
          |
          |
          V
     +----------+
     |PREROUTING|
     +----------+
     |   raw    |  <--------------+
     |  mangle  |                 |
     |   nat    |                 |
     +----------+                 |
          |                       |
          |                       |
       Routing                    |
    +- Decision -+                |
    |            |                |
    |            |                |
    V            V                |
  Local        Remote             |
Destination   Destination         |
    |            |                |
    |            |                |
    V            V                |
+--------+  +---------+           |
| INPUT  |  | FORWARD |           |
+--------+  +---------+           |
| mangle |  | mangle  |           |
| filter |  | filter  |           |
+--------+  +---------+           |
    |            |                |
    |            |                |
    V            |                |
  Local          |                |
 Machine         |                |
    |            |                |
    |            |                |
    V            |                |
 Routing         |                |
 Decision        |                |
    |            |                |
    |            |                |
    V            |                |
+--------+       |                |
| OUTPUT |       |                |
+--------+       |                |
|  raw   |       |                |
| mangle |       |                |
|  nat   |       |                |
| filter |       |                |
+--------+       |                |
    |            |                |
    |      +-------------+        |
    |      | POSTROUTING |      Local
    +----> +-------------+ --> Traffic
           |   mangle    |
           |     nat     |
           +-------------+
                 |
                 |
                 V
              Outgoing
              Traffic
	
	

41.2.1. Getting Started

Redhat / CentOS

You can check to see if iptables is installed on your system by:

[root@database ~]# rpm -q iptables
iptables-1.3.5-5.3.el5_4.1
		

And to see if iptables is actually running, we can check that the iptables modules are loaded and use the -L switch to inspect the currently loaded rules:

[root@database ~]# lsmod | grep ip_tables
ip_tables              55201  2 iptable_nat,iptable_filter
x_tables               50505  6 ipt_MASQUERADE,iptable_nat,xt_state,ipt_REJECT,xt_tcpudp,ip_tables

		
[root@database ~]# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere            udp dpt:bootps
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:bootps

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             192.168.122.0/24    state RELATED,ESTABLISHED
ACCEPT     all  --  192.168.122.0/24     anywhere
ACCEPT     all  --  anywhere             anywhere
REJECT     all  --  anywhere             anywhere            reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere            reject-with icmp-port-unreachable

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

		

顯示行號

# iptables --list -nv --line-number 
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1      139 15916 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
2        1    92 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           
3        0     0 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
4        1    40 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:22
5        0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:80
6        0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:25
7        0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:20
8        2   104 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:21
9        1    40 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 137 packets, 24640 bytes)
num   pkts bytes target     prot opt in     out     source               destination		
		

41.2.1.1. CentOS/Redhat TUI 工具

If iptables is not running, you can enable it by running:

# lokkit --enabled --selinux=disabled
# lokkit --disabled --selinux=disabled
			
# lokkit --enabled

# ls /etc/sysconfig/iptables*
iptables         iptables-config  iptables.old

# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-firewall
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

# lokkit --disabled
# ls /etc/sysconfig/iptables*
iptables-config  iptables.old
			

lokkit --enabled作用就是產生/etc/sysconfig/iptables檔案。--disabled的作用是將更名為iptables.old

# system-config-securitylevel
			

41.2.2. 用戶自定義規則連

User-defined Chain

41.2.2.1. Chains List

列出規則鏈

 列出INPUT,OUTPUT,FORWARD規則
iptables -L

列出NAT規則
iptables -t nat -L

列出過濾規則
iptables -t filter -L
			

顯示行號

# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination
1    ACCEPT     all  --  anywhere             192.168.2.10
2    ACCEPT     all  --  anywhere             192.168.2.11
3    ACCEPT     all  --  anywhere             192.168.2.12
4    ACCEPT     all  --  anywhere             192.168.2.13
5    ACCEPT     all  --  anywhere             192.168.2.14
6    DROP       all  --  anywhere             anywhere

Chain FORWARD (policy ACCEPT)
num  target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination
			

顯示包轉發

# iptables -L -v
Chain INPUT (policy ACCEPT 881 packets, 146K bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     all  --  tun0   any     anywhere             192.168.2.10
    0     0 ACCEPT     all  --  tun0   any     anywhere             192.168.2.11
    0     0 ACCEPT     all  --  tun0   any     anywhere             192.168.2.12
    0     0 ACCEPT     all  --  tun0   any     anywhere             192.168.2.13
    0     0 ACCEPT     all  --  tun0   any     anywhere             192.168.2.14
    0     0 DROP       all  --  tun0   any     anywhere             anywhere

Chain FORWARD (policy ACCEPT 1190 packets, 440K bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy ACCEPT 888 packets, 437K bytes)
 pkts bytes target     prot opt in     out     source               destination
			
# iptables -L -t nat -v
Chain PREROUTING (policy ACCEPT 509 packets, 43877 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain POSTROUTING (policy ACCEPT 94 packets, 6038 bytes)
 pkts bytes target     prot opt in     out     source               destination
  163 13140 MASQUERADE  all  --  any    br0     10.8.0.0/24          anywhere

Chain OUTPUT (policy ACCEPT 94 packets, 6038 bytes)
 pkts bytes target     prot opt in     out     source               destination
			

41.2.2.2. Chains Refresh

刷新規則

/sbin/iptables -F
/sbin/iptables -F -t filter
/sbin/iptables -F -t nat
/sbin/iptables -t nat -P PREROUTING ACCEPT
/sbin/iptables -t nat -P POSTROUTING ACCEPT
/sbin/iptables -P INPUT ACCEPT
/sbin/iptables -P OUTPUT ACCEPT
/sbin/iptables -P FORWARD ACCEPT
			

41.2.2.3. Chains Admin

創建新鏈

				iptables -N netkiller
			

刪除新鏈

				# iptables -X netkiller
			

41.2.2.4. 重置

例 41.1. /etc/sysconfig/iptables

/sbin/iptables -F
/sbin/iptables -F -t filter
/sbin/iptables -F -t nat
/sbin/iptables -t nat -P PREROUTING ACCEPT
/sbin/iptables -t nat -P POSTROUTING ACCEPT
/sbin/iptables -t nat -P OUTPUT ACCEPT
/sbin/iptables -P INPUT ACCEPT
/sbin/iptables -P OUTPUT ACCEPT
/sbin/iptables -P FORWARD ACCEPT

sysctl net.ipv4.ip_forward=1
				

/etc/sysconfig/iptables

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited				
				

41.2.3. Protocols 協議

-p tcp
-p udp
		

41.2.4. Interfaces 網絡適配器介面

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i eth0 -j ACCEPT
iptables -A INPUT -i ppp0 -j ACCEPT
		

41.2.5. 源IP地址

# Accept packets from trusted IP addresses
 iptables -A INPUT -s 192.168.0.4 -j ACCEPT # change the IP address as appropriate

# Accept packets from trusted IP addresses
 iptables -A INPUT -s 192.168.0.0/24 -j ACCEPT  # using standard slash notation
 iptables -A INPUT -s 192.168.0.0/255.255.255.0 -j ACCEPT # using a subnet mask


# Accept packets from trusted IP addresses
 iptables -A INPUT -s 192.168.0.4 -m mac --mac-source 00:50:8D:FD:E6:32 -j ACCEPT
		

多地址輸入方法

iptables -t filter -A INPUT -s 192.168.1.1,2.2.2.2,10.10.10.10 -j ACCEPT		
		

連續範圍

-A INPUT -i eth0 -m iprange --src-range 192.168.1.90-192.168.1.101 -j ACCEPT		
		

41.2.6. Ports 連接埠

# Accept tcp packets on destination port 6881 (bittorrent)
 iptables -A INPUT -p tcp --dport 6881 -j ACCEPT
		

41.2.6.1. range

# Accept tcp packets on destination ports 6881-6890
iptables -A INPUT -p tcp --dport 6881:6890 -j ACCEPT
			

41.2.6.2. multiport

多連接埠

-A INPUT -s 116.24.13.13/32 -p tcp -m tcp -m multiport --dports 21,20 -j ACCEPT
			

41.2.7. NAT

41.2.7.1. Redirect

重定向規則

連接埠重定向
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 21 -j REDIRECT --to-port 2401

將80連接埠重定向到8080
# iptables -t nat -A PREROUTING -j REDIRECT -p tcp --destination-port 80 --to-ports 8080
			

連接埠轉發

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A PREROUTING -d 192.168.3.9 -p tcp -m tcp --dport 1000 -j DNAT --to-destination 192.168.3.137:8080
iptables -t nat -A POSTROUTING -s 192.168.3.0/255.255.255.0 -d 192.168.3.137 -p tcp -m tcp --dport 8080 -j SNAT --to-source 192.168.3.9
			

41.2.7.2. Postrouting and IP Masquerading

			
iptables -P FORWARD ACCEPT
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -j MASQUERADE
iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -o eth0 -j MASQUERADE

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -t nat -I POSTROUTING -j MASQUERADE
sudo iptables -t nat -A POSTROUTING -j MASQUERADE -s 172.16.0.0/24 -d 0.0.0.0/0
sudo iptables -t nat -A POSTROUTING -j MASQUERADE -o eth1 -s 172.16.1.0/24 -d 0.0.0.0/0
sudo iptables -t nat -A POSTROUTING -j MASQUERADE -p tcp -o eth1 -s 172.16.1.0/24 -d 0.0.0.0/0
			
			

41.2.7.3. Prerouting

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to 172.31.0.23:80
		

If you have a default policy of DROP in your FORWARD chain, you must append a rule to forward all incoming HTTP requests so that destination NAT routing is possible. To do this, use the following command:

iptables -A FORWARD -i eth0 -p tcp --dport 80 -d 172.31.0.23 -j ACCEPT
		

This rule forwards all incoming HTTP requests from the firewall to the intended destination; the Apache HTTP Server behind the firewall.

41.2.7.4. DNAT and SNAT

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A PREROUTING -d 202.103.96.10 -j DNAT --to-destination 192.168.0.10
iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -j SNAT --to-source 202.96.244.56
		

41.2.7.5. DMZ zone

#
# DMZ zone
#
$iptables -t nat -A PREROUTING -p TCP -m multiport -i eth0 --dport 22,25,113,80,8080 -j DNAT --to 10.0.0.10
$iptables -t nat -A PREROUTING -p UDP -i eth0 --dport 25 -j DNAT --to-destination 10.0.0.10
			

DNAT ppp0/eth0

			
iptables -t nat -A PREROUTING -p tcp -i ppp0 --dport 80 -j DNAT --to-destination <web server ip>
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.0.4.2:80
			
			

41.2.8. Module(模組)

41.2.8.1. IPTables and Connection Tracking


NEW — A packet requesting a new connection, such as an HTTP request.

ESTABLISHED — A packet that is part of an existing connection.

RELATED — A packet that is requesting a new connection but is part of an existing connection. For example, FTP uses port 21 to establish a connection, but data is transferred on a different port (typically port 20).

INVALID — A packet that is not part of any connections in the connection tracking table.

放行已經啟動的服務

-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
			
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
			

禁止新的連接埠listen,在防火牆啟動後,不在允許啟動任何新的連接埠。

-A INPUT -m state --state INVALID,NEW -j DROP		
			

41.2.8.2. string

iptables -m string -h
			
# iptables -A INPUT -p tcp --dport 80 -m string --algo bm --string "XXDD0S" -j DROP
			

41.2.8.3. connlimit

限制同一IP同時最多100個http連接
iptables -I INPUT -p tcp --syn --dport 80 -m connlimit --connlimit-above 100 -j REJECT

只允許每組C類IP同時100個http連接
iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 100 --connlimit-mask 24 -j REJECT

只允許每個IP同時5個80連接埠轉發,超過的丟棄
iptables -I FORWARD -p tcp --syn --dport 80 -m connlimit --connlimit-above 5 -j DROP

限制某IP最多同時100個http連接
iptables -A INPUT -s xxx.xxx.xxx.xxx -p tcp --syn --dport 80 -m connlimit --connlimit-above 100 -j REJECT		
			

限制多少IP連結你的伺服器

# allow 2 telnet connections per client host
iptables -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT

# you can also match the other way around:
iptables -p tcp --syn --dport 23 -m connlimit ! --connlimit-above 2 -j ACCEPT

# limit the nr of parallel http requests to 16 per class C sized
# network (24 bit netmask)
iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16 \
        --connlimit-mask 24 -j REJECT

# Skip proxy server IP 1.2.3.4 from this kind of limitations:
iptables -A INPUT -p tcp --syn --dport 80 -d ! 1.2.3.4 -m connlimit --connlimit-above 20 -j REJECT --reject-with tcp-reset

iptables -A INPUT -i ppp0 -p tcp --syn -m connlimit --connlimit-above 15 -j DROP
iptables -A INPUT -s 192.186.0.0/24 -p tcp --syn -m connlimit --connlimit-above 15 -j DROP
iptables -I INPUT -p tcp --dport 80 -m connlimit --connlimit-above 50 -j REJECT
			
iptables -A INPUT -p tcp -m state --state NEW -m tcp --dport 443 --syn -m connlimit --connlimit-above 50 -j REJECT
			

例 41.2. connlimit 實例

OS: CentOS

# Generated by iptables-save v1.3.5 on Thu Mar  1 19:01:23 2012
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [548:1014604]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A OUTPUT -p udp -m udp --dport 53 -j ACCEPT
-A OUTPUT -p udp -m udp --dport 161 -j ACCEPT
-A OUTPUT -p udp -j DROP
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p esp -j ACCEPT
-A RH-Firewall-1-INPUT -p ah -j ACCEPT
-A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 3306 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN -m connlimit --connlimit-above 50 --connlimit-mask 32 -j REJECT --reject-with icmp-port-unreachable
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 --tcp-flags FIN,SYN,RST,ACK SYN -m connlimit --connlimit-above 50 --connlimit-mask 32 -j REJECT --reject-with icmp-port-unreachable
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Thu Mar  1 19:01:23 2012
				

CentOS

# Firewall configuration written by system-config-firewall
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 443 --tcp-flags FIN,SYN,RST,ACK SYN -m connlimit --connlimit-above 50 --connlimit-mask 32 -j REJECT --reject-with icmp-port-unreachable
-A INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
				

41.2.8.4. recent

限制每IP在一定的時間(比如60秒)內允許新建立最多100個http連接數

iptables -A INPUT -p tcp --dport 80 -m recent --name BAD_HTTP_ACCESS --update --seconds 60 --hitcount 100 -j REJECT
iptables -A INPUT -p tcp --dport 80 -m recent --name BAD_HTTP_ACCESS --set -j ACCEPT				
			

41.2.8.5. limit

iptables -A INPUT -p icmp -m limit --limit 3/s -j LOG --log-level INFO --log-prefix "ICMP packet IN: "
			
iptables -N syn-flood
iptables -A INPUT -p tcp --syn -j syn-flood
iptables -I syn-flood -p tcp -m limit --limit 3/s --limit-burst 6 -j RETURN
iptables -A syn-flood -j REJECT
			

將丟棄包情況記入日誌

新建LOGGING鏈:
iptables -N LOGGING

將所有接收包導入LOGGING 鏈中:
iptables -A INPUT -j LOGGING

設置日誌首碼與日誌級別:
iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables Packet Dropped: " --log-level 7

最後將包倒向DROP,將包丟棄:
iptables -A LOGGING -j DROP			
			

41.2.8.6. nth

41.2.8.6.1. DNAT

利用iptables 實現負載均衡

iptables -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.101:80
iptables -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.102:80
iptables -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.103:80			
				
41.2.8.6.2. SNAT

SNAT 是控製出去的IP

				
# Generated by iptables-save v1.4.21 on Mon Nov 28 21:25:50 2016
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [27:3804]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT
-A INPUT -s 47.90.44.87 -p tcp -m state --state NEW -m tcp --dport 10050 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Mon Nov 28 21:25:50 2016
# Generated by iptables-save v1.4.21 on Mon Nov 28 21:25:50 2016
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -o enp2s0f0 -p tcp -m state --state NEW -m tcp -m statistic --mode nth --every 5 --packet 0 -j SNAT --to-source 104.23.14.186
-A POSTROUTING -o enp2s0f0 -p tcp -m state --state NEW -m tcp -m statistic --mode nth --every 5 --packet 0 -j SNAT --to-source 104.23.14.187
-A POSTROUTING -o enp2s0f0 -p tcp -m state --state NEW -m tcp -m statistic --mode nth --every 5 --packet 0 -j SNAT --to-source 104.23.14.188
-A POSTROUTING -o enp2s0f0 -p tcp -m state --state NEW -m tcp -m statistic --mode nth --every 5 --packet 0 -j SNAT --to-source 104.23.14.189
-A POSTROUTING -o enp2s0f0 -p tcp -m state --state NEW -m tcp -m statistic --mode nth --every 5 --packet 0 -j SNAT --to-source 104.23.14.190
COMMIT
# Completed on Mon Nov 28 21:25:50 2016
				
				

使用 curl 測試

				
$ curl http://ip.cn
$ curl http://ip.cn
$ curl http://ip.cn
$ curl http://ip.cn
$ curl http://ip.cn
				
				

你會發現每次訪問的IP均不同

41.2.8.7. random 模組

			
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m statistic --mode random --probability .25 -j DNAT --to-destination 10.10.0.1:80
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m statistic --mode random --probability .25 -j DNAT --to-destination 10.10.0.2:80
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m statistic --mode random --probability .25 -j DNAT --to-destination 10.10.0.3:80
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m statistic --mode random --probability .25 -j DNAT --to-destination 10.10.0.4:80
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m statistic --mode random --probability .25 -j DNAT --to-destination 10.10.0.5:80
			
			

41.2.9. IPV6

		
[root@linux iptables]# modprobe ipv6
[root@linux iptables]# modprobe ip6_tables
[root@linux iptables]# [ ! -f /proc/net/ip6_tables_names ] && echo "Current kernel doesn't support? 'ip6tables' firewalling (IPv6)!"
[root@linux iptables]# ip6tables -A INPUT -i eth0 -p tcp -s 3ffe:ffff:100::1/128 --dport 22 -j ACCEPT
		
		

41.2.10. iptables-xml - Convert iptables-save format to XML

41.2.11. access.log IP封鎖腳本

#!/bin/bash

ACCCESS_LOG=/tmp/myid.access.log
TIMEPOINT='23/May/2012'
BLACKLIST=/var/tmp/black
WHITELIST=/var/tmp/white
if [ ! -f ${BLACKLIST} ]; then
    touch ${BLACKLIST}
fi

if [ ! -f ${WHITELIST} ]; then
    touch ${WHITELIST}
fi

for deny in $(grep ${TIMEPOINT} ${ACCCESS_LOG} | awk '{print $1}' | awk -F'.' '{print $1"."$2"."$3"."$4}' | sort | uniq -c | sort -r -n | head -n 30| awk '{print $2}')
do

    if [ $(grep -c $deny ${WHITELIST}) -ne 0 ]; then
        echo 'Allow IP:' $deny
	continue
    fi

    if [ $(grep -c $deny ${BLACKLIST}) -eq 0 ] ; then

	echo 'Deny IP:' $deny
        echo $deny >> ${BLACKLIST}
        iptables -I INPUT -p tcp --dport 443 -s $deny -j DROP
        iptables -I INPUT -p tcp --dport 80 -s $deny -j DROP
    fi
done
		

41.2.12. Example

Common Chains Filtering

41.2.12.1. INPUT Rule Chains

41.2.12.1.1. OpenSSH
# Accept tcp packets on destination port 22 (SSH)
 iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Accept tcp packets on destination port 22 (SSH) from private LAN
 iptables -A INPUT -p tcp -s 192.168.0.0/24 --dport 22 -j ACCEPT
			
41.2.12.1.2. FTP
/sbin/iptables -A INPUT -p tcp --dport 21 -j ACCEPT
/sbin/iptables -A INPUT -p tcp --dport 20 -j ACCEPT
			
41.2.12.1.3. DNS
iptables -A INPUT -i eth0 -p tcp --dport 53   -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 53   -j ACCEPT
			
41.2.12.1.4. WWW
# WWW
/sbin/iptables -A INPUT -p tcp --dport 80 -j ACCEPT
# HTTPS
/sbin/iptables -A INPUT -p tcp --dport 443 -j ACCEPT
# Tomcat
/sbin/iptables -A INPUT -p tcp --dport 8080 -j ACCEPT
			
41.2.12.1.5. SOCKS5
/sbin/iptables -A INPUT -p tcp --dport 1080 -j ACCEPT
			
41.2.12.1.6. Mail Server
# SMTP
/sbin/iptables -A INPUT -p tcp --dport 25 -j ACCEPT
# SMTPS
/sbin/iptables -A INPUT -p tcp --dport 465 -j ACCEPT
# POP3
/sbin/iptables -A INPUT -p tcp --dport 110 -j ACCEPT
# POP3S
/sbin/iptables -A INPUT -p tcp --dport 995 -j ACCEPT
# IMAP
/sbin/iptables -A INPUT -p tcp --dport 143 -j ACCEPT
# IMAPS
/sbin/iptables -A INPUT -p tcp --dport 993 -j ACCEPT
			
41.2.12.1.7. MySQL
/sbin/iptables -A INPUT -p tcp --dport 3306 -j ACCEPT
			
41.2.12.1.8. PostgreSQL
/sbin/iptables -A INPUT -p tcp --dport 5432 -j ACCEPT
			
41.2.12.1.9. DHCP
iptables -A INPUT -p UDP -i eth0 --dport 67 -j ACCEPT
iptables -A INPUT -p UDP -i eth0 --dport 68 -j ACCEPT
			
41.2.12.1.10. Samba
/sbin/iptables -A INPUT -p tcp -s 192.168.0.0/24 --dport 137 -j ACCEPT
iptables -A INPUT -p tcp -s 192.168.0.0/24 --dport 145 -j ACCEPT
iptables -A INPUT -p udp -s 192.168.0.0/24 --dport 138 -j ACCEPT
iptables -A INPUT -p udp -s 192.168.0.0/24 --dport 139 -j ACCEPT
			
41.2.12.1.11. ICMP


accept_redirects
# echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects
or
# sysctl net.ipv4.conf.all.accept_redirects="0"

使自己不能ping 通 127.0.0.1
iptables -A INPUT -s 127.0.0.1 -p icmp -j DROP

192.168.0.0/24 網段無法ping能本機
iptables -A INPUT -s 192.168.0.0/24 -p icmp -j DROP

禁所有機器
# iptables -A INPUT -s 0/0 -p icmp -j DROP

# ICMP(PING) 接受 ! echo-request
iptables -A INPUT -p icmp --icmp-type ! echo-request -j ACCEPT
			
41.2.12.1.12. 禁止IP訪問自己
$sudo iptables -A INPUT -s 192.168.0.253 -j DROP
			
41.2.12.1.13. DENY
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -j DROP
			

41.2.12.2. OUTPUT Rule Chains

41.2.12.2.1. outbound
# Open ports for outbound established connections
$IPT -A OUTPUT -p tcp -s $NET -d 0/0 --destination-port 1:65535 -j ACCEPT
$IPT -A OUTPUT -p udp -s $NET -d 0/0 --destination-port 1:65535 -j ACCEPT
			
41.2.12.2.2. ICMP


本地不允許ping 192.168.0.0/24
iptables -A OUTPUT -s 192.168.0.0/24 -p icmp -j DROP

禁所本地ping任何機器
# iptables -A OUTPUT -s 0/0 -p icmp -j DROP

# ICMP(PING) 接受 ! echo-request
iptables -A OUTPUT -p icmp --icmp-type ! echo-request -j ACCEPT

41.2.12.2.3. NFS
iptables -A OUTPUT -p tcp --dport 2049 -j REJECT
			
41.2.12.2.4. SSH
iptables -A OUTPUT -p tcp -m multiport --dports 22 -j REJECT
			
41.2.12.2.5. 禁止自己訪問某個IP
# iptables -A OUTPUT -d 192.168.0.253 -j DROP
iptables -A OUTPUT -p udp -j DROP
iptables -A OUTPUT -d 125.211.210.46 -j DROP
			

41.2.12.3. Forward

iptables -A FORWARD -i eth1 -j ACCEPT
		
# Network 1 forwarded outgoing client request to network 2
iptables -A FORWARD -i eth1 -p tcp -s 192.168.1.0/24 -d 192.168.2.0/24 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A FORWARD -o eth1 -p tcp -s 192.168.2.0/24 -d 192.168.1.0/24 -m state --state ESTABLISHED,RELATED -j ACCEPT
		
41.2.12.3.1. TCPMSS
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
			

41.2.12.4. Malicious Software and Spoofed IP Addresses

# The following rules drop all TCP traffic that attempts to use port 31337:
iptables -A OUTPUT -o eth0 -p tcp --dport 31337 --sport 31337 -j DROP
iptables -A FORWARD -o eth0 -p tcp --dport 31337 --sport 31337 -j DROP
		

41.2.12.5. /etc/sysconfig/iptables 操作系統預設配置

例 41.3. CentOS 5.6

# iptables-save
# Generated by iptables-save v1.3.5 on Sat Dec 31 18:29:51 2011
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1516:131654]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -i eth0 -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p esp -j ACCEPT
-A RH-Firewall-1-INPUT -p ah -j ACCEPT
-A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 1521 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 3306 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 23 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m state --state NEW -m udp --dport 137 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m state --state NEW -m udp --dport 138 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 139 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 445 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 2049 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Sat Dec 31 18:29:51 2011
			
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -i eth3 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth2 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth0 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth1 -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT


# Generated by iptables-save v1.3.5 on Wed May 23 10:58:21 2012
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [43:8584]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -i eth3 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth2 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth0 -j ACCEPT
-A RH-Firewall-1-INPUT -i eth1 -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p esp -j ACCEPT
-A RH-Firewall-1-INPUT -p ah -j ACCEPT
-A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 --tcp-flags FIN,SYN,RST,ACK SYN -m connlimit --connlimit-above 50 --connlimit-mask 32 -j REJECT --reject-with icmp-port-unreachable
-A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Wed May 23 10:58:21 2012