大家好，我是架构君，一个会写代码吟诗的架构师。今天说一说udp端口转发 Linux,Linux iptables 端口转发[通俗易懂],希望能够帮助大家进步!!!
准备：
1， UDP端口范围映射
2， tcp 端口范围映射
3， 本机端口转发
4， 单个端口转发
打开转发
root@CentOS ~# cat /etc/sysctl.conf | grep net.ipv4.ip_forward
net.ipv4.ip_forward = 1
清空规则，修改默认策略，重要数据请备份
root@CentOS ~# iptables -F -t nat
root@CentOS ~# iptables -X -t nat
root@CentOS ~# iptables -P INPUT DROP
root@CentOS ~# iptables -L -t nat
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
root@CentOS ~#
删除reject
root@CentOS ~# vim /etc/sysconfig/iptables
root@CentOS ~# service iptables restart
1， UDP端口范围映射
一一匹配：
root@CentOS ~# iptables -t nat -A PREROUTING -p udp --dport 5000:6000 -j DNAT --to 192.168.66.2:5000-6000
【注意】这样写，将导致不可预测的端口转发匹配：
root@CentOS ~# iptables -t nat -A PREROUTING -p udp --dport 5000:5010 -j DNAT --to 192.168.66.2:6000-6010
【nat内机器：192.168.66.2】端口转发匹配验证，输出源端口是9999
root@CentOS ~# tcpdump -i eth0 -tnn port 9999
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
IP 172.16.20.245.9999 > 192.168.66.2.5500: UDP, length 1
IP 172.16.20.245.9999 > 192.168.66.2.5500: UDP, length 1
IP 172.16.20.245.9999 > 192.168.66.2.5501: UDP, length 1
IP 172.16.20.245.9999 > 192.168.66.2.5501: UDP, length 1
【nat外机器：172.16.20.245】发送给nat机器，发出的数据包源端口是9999， 目的端口是5500-5555
sudo nc -v -u -p 9999 172.16.20.183 5500-5555
端口转发双向通信验证：
nat里面的机器打开监听：
root@CentOS ~# nc -l -u 5555
nat外面的机器向nat 发送数据
nc -u 172.16.20.183 5555
互发数据，双方是可以收到的。
可以发现：端口映射完全匹配，双通互发数据成功！
2， tcp 端口范围映射
tcp 端口范围映射：
root@CentOS ~# iptables -t nat -A PREROUTING -p tcp --dport 2000:2500 -j DNAT --to 192.168.66.2:2000-2500
验证：
接收端：【nat内机器：192.168.66.2】
root@CentOS ~# tcpdump -i eth0 -tnn portrange 2000-2500
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
IP 172.16.20.245.37446 > 192.168.66.2.2000: Flags S, seq 1083771445, win 29200, options mss 1460,sackOK,TS val 3864340 ecr 0,nop,wscale 7, length 0
IP 192.168.66.2.2000 > 172.16.20.245.37446: Flags R., seq 0, ack 1083771446, win 0, length 0
IP 172.16.20.245.47912 > 192.168.66.2.2001: Flags S, seq 629593170, win 29200, options mss 1460,sackOK,TS val 3864344 ecr 0,nop,wscale 7, length 0
IP 192.168.66.2.2001 > 172.16.20.245.47912: Flags R., seq 0, ack 629593171, win 0, length 0
IP 172.16.20.245.34816 > 192.168.66.2.2002: Flags S, seq 680276410, win 29200, options mss 1460,sackOK,TS val 3864345 ecr 0,nop,wscale 7, length 0
IP 192.168.66.2.2002 > 172.16.20.245.34816: Flags R., seq 0, ack 680276411, win 0, length 0
IP 172.16.20.245.37508 > 192.168.66.2.2003: Flags S, seq 1070666075, win 29200, options mss 1460,sackOK,TS val 3864345 ecr 0,nop,wscale 7, length 0
IP 192.168.66.2.2003 > 172.16.20.245.37508: Flags R., seq 0, ack 1070666076, win 0, length 0
发送端：【nat外机器：172.16.20.245】发送给nat机器:
sudo nc -z -w1 -v 172.16.20.183 2000-2500
nc: connect to 172.16.20.183 port 2000 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2001 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2002 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2003 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2004 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2005 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2006 (tcp) failed: Connection refused
nc: connect to 172.16.20.183 port 2007 (tcp) failed: Connection refused
可以看见，虽然连接失败，但是发送的seq和ack回应包都有了，就差握手成功了。
3， 本机端口转发
root@CentOS ~# iptables -t nat -A PREROUTING -p tcp --dport 1234 -j REDIRECT --to-ports 2345
root@CentOS ~# nc -l -k 2345 #开启监听
1，
局域网其他主机直接来访问本机2345端口：看看tcpdump输出
chunli@ubuntu~$ nc 172.16.20.183 2345 #远程机访问本机172.16.20.183 2345
本机tcpdump输出
root@CentOS ~# tcpdump -i eth0 host 172.16.20.245 -tnn
IP 172.16.20.245.44706 > 172.16.20.183.2345: Flags S, seq 33366406, win 29200, options mss 1460,sackOK,TS val 4001328 ecr 0,nop,wscale 7, length 0
IP 172.16.20.183.2345 > 172.16.20.245.44706: Flags R., seq 0, ack 33366407, win 0, length 0
2，局域网其他主机直接来访问本机1234端口：看看tcpdump输出
chunli@ubuntu~$ nc 172.16.20.183 1234 #远程机访问本机172.16.20.183 1234
tcpdump在本机看一下：
root@CentOS ~# tcpdump -i eth0 host 172.16.20.245 -tnn
IP 172.16.20.245.47332 > 172.16.20.183.1234: Flags S, seq 3622624416, win 29200, options mss 1460,sackOK,TS val 4047126 ecr 0,nop,wscale 7, length 0
IP 172.16.20.183.1234 > 172.16.20.245.47332: Flags S., seq 123535638, ack 3622624417, win 14480, options mss 1460,sackOK,TS val 12018501 ecr 4047126,nop,wscale 6, length 0
IP 172.16.20.245.47332 > 172.16.20.183.1234: Flags ., ack 1, win 229, options nop,nop,TS val 4047126 ecr 12018501, length 0
IP 172.16.20.245.47332 > 172.16.20.183.1234: Flags P., seq 1:2, ack 1, win 229, options nop,nop,TS val 4047282 ecr 12018501, length 1
IP 172.16.20.183.1234 > 172.16.20.245.47332: Flags ., ack 2, win 227, options nop,nop,TS val 12019122 ecr 4047282, length 0
IP 172.16.20.245.47332 > 172.16.20.183.1234: Flags P., seq 2:3, ack 1, win 229, options nop,nop,TS val 4047325 ecr 12019122, length 1
IP 172.16.20.183.1234 > 172.16.20.245.47332: Flags ., ack 3, win 227, options nop,nop,TS val 12019297 ecr 4047325, length 0
IP 172.16.20.245.47332 > 172.16.20.183.1234: Flags P., seq 3:4, ack 1, win 229, options nop,nop,TS val 4047353 ecr 12019297, length 1
可以看到三次握手成功！
4， 单个端口转发
端口转发 tcp模式：将访问本机1122端口数据包转发给192.168.66.2:5566
iptables -t nat -A PREROUTING -p tcp --dport 1122 -j DNAT --to-destination 192.168.66.2:5566
端口转发 udp模式：将访问本机2233端口数据包转发给192.168.66.2:4455
iptables -t nat -A PREROUTING -p udp --dport 2233 -j DNAT --to-destination 192.168.66.2:4455
