3.使用iptable实现: 放行ssh,telnet, ftp, web服务80端口，其他端口服务全部拒绝

使用iptable实现: 放行ssh,telnet, ftp, web服务80端口，其他端口服务全部拒绝

服务端口：

Ssh：22

Telnet: tcp 23

 ftp：tcp 20 21

 Web: 80 443

[root@centos7 ~]# iptables -A INPUT -p tcp -m multiport –dport 21,22,23,80,443 -j ACCEPT

[root@centos7 ~]# iptables -A INPUT -j REJECT

[root@centos7 ~]#     

[root@centos7 ~]# iptables -nvL

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)

 pkts bytes target     prot opt in     out     source               destination         

  116  6768 ACCEPT     tcp  —  *      *       0.0.0.0/0            0.0.0.0/0            multiport dports 21,22,23,80

    0     0 REJECT     all  —  *      *       0.0.0.0/0            0.0.0.0/0            reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)

 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 20 packets, 2384 bytes)

 pkts bytes target     prot opt in     out     source               destination         

[root@centos7 ~]#