ASA的twice-nat将互联网访问的源地址转换为内网接口地址测试

一.测试拓扑

二.测试思路

1. 不考虑网络拓扑的合理性，只是考虑网络是否可通
   

2. 外网访问内部服务器在防火墙上映射的公网地址不通是因为R1的默认路由指向的不是防火墙，出现了非对称路由问题，导致TCP连接来回路径不一致而会话失败

3. 如果把外网访问内部服务器的源地址转换为防火墙内网接口地址，则不会出现非对称路由问题

三.基本配置

1. 路由器Server：

   interface FastEthernet0/0
        ip address 192.168.1.8 255.255.255.0
        no shut
   ip route 0.0.0.0 0.0.0.0 192.168.1.1
   

2. 路由器R1：

   interface Ethernet0/0
        ip address 192.168.2.1 255.255.255.0
        no shut!         
   interface Ethernet0/1
        ip address 192.168.3.1 255.255.255.0
        no shut
   interface Ethernet0/2
        ip address 192.168.1.1 255.255.255.0
        no shut!
   ip route 0.0.0.0 0.0.0.0 192.168.3.254
   

3. 路由器R2：

   interface Ethernet0/0
    ip address 202.100.2.1 255.255.255.0
        ip nat outside
        no shut

   interface Ethernet0/1
        ip address 192.168.3.254 255.255.255.0
        ip nat inside
        no shut
   ip route 0.0.0.0 0.0.0.0 202.100.2.2
   ip route 192.168.0.0 255.255.0.0 192.168.3.1

   
   ip nat inside source list PAT interface Ethernet0/0 overload
   ip access-list extended PAT
    permit ip 192.168.0.0 0.0.255.255 any
   

4. 防火墙ASA842：

   interface GigabitEthernet0
        nameif Outside
        security-level 0
        ip address 202.100.1.1 255.255.255.0 
   interface GigabitEthernet1
        nameif Inside
        security-level 100
        ip address 192.168.2.254 255.255.255.0 
   
   route Outside 0.0.0.0 0.0.0.0 202.100.1.2 1
   route Inside 192.168.0.0 255.255.0.0 192.168.2.1 1

5. 路由器Internet：

   interface Loopback0
        ip address 61.1.1.1 255.255.255.0
   interface FastEthernet0/0
        ip address 202.100.1.2 255.255.255.0
        no shut
   interface FastEthernet0/1
        ip address 202.100.2.2 255.255.255.0
        no shut

   
   

四.防火墙twice-nat相关配置

1. 定义内网服务器对象：

   object network ServerReal
        host 192.168.1.8

2. 定义内网服务器映射后的公网IP对象：

   object network ServerMap

   host 202.100.1.8
   

3. 配置twice-nat：

   转换前-----源地址：any 目标地址：内网服务器映射后的公网IP
   

   转换后-----源地址：防火墙inside口地址 目标地址：内网服务器实际

   IP nat (Outside,Inside) source dynamic any interface destination static ServerMap ServerReal

4. 定义防火墙外网口策略：

   access-list Outside extended permit ip any object ServerReal

   ---注意这些是服务器的实际地址，而不是映射后的地址

5. 应用防火墙外网口策略：

   access-group Outside in interface Outside
   

6. 测试：

   
   

   Internet#telnet 202.100.1.8
   Trying 202.100.1.8 ... Open
   
   
   User Access Verification
   
   Password: 
   Server>show user
   % Ambiguous command:  "show user"
   Server>show users
       Line       User       Host(s)              Idle       Location
      0 con 0                idle                 00:05:42   
   *  2 vty 0                idle                 00:00:00 192.168.2.254
   
     Interface    User               Mode         Idle     Peer Address
   
   Server>q
   
   [Connection to 202.100.1.8 closed by foreign host]
   Internet#

   -----从公网来的防火墙已经作了源地址转换

   Server#ping 61.1.1.1
   
   Type escape sequence to abort.
   Sending 5, 100-byte ICMP Echos to 61.1.1.1, timeout is 2 seconds:
   !!!!!
   Success rate is 100 percent (5/5), round-trip min/avg/max = 44/80/144 ms
   

   Server#

   Internet#debug ip icmp 
   ICMP packet debugging is on
   Internet#
   *Aug 22 13:02:57.787: ICMP: echo reply sent, src 61.1.1.1, dst 202.100.2.1
   *Aug 22 13:02:57.967: ICMP: echo reply sent, src 61.1.1.1, dst 202.100.2.1
   *Aug 22 13:02:58.067: ICMP: echo reply sent, src 61.1.1.1, dst 202.100.2.1
   *Aug 22 13:02:58.123: ICMP: echo reply sent, src 61.1.1.1, dst 202.100.2.1
   *Aug 22 13:02:58.127: ICMP: echo reply sent, src 61.1.1.1, dst 202.100.2.1
   Internet#
   

   ------Server可以正常从R2路由器PAT上公网

五.后记

1. 多个内网地址，多个公网地址，都是一对一映射情况

   可以按上面格式配置多个映射，并且都是映射到防火墙内网口地址

   object network ServerMap
   

        host 202.100.1.8
   

   object network ServerReal
        host 192.168.1.8

   object network R1Map
        host 202.100.1.18

   object network R1Real
        host 192.168.1.1
   

   
   

   nat (Outside,Inside) source dynamic any interface destination static ServerMap ServerReal
   

   nat (Outside,Inside) source dynamic any interface destination static R1Map R1Real

   
   

   access-list Outside extended permit tcp any object ServerReal eq telnet 
   access-list Outside extended permit tcp any object R1Real eq telnet 
   access-group Outside in interface Outside

2. 多个内网地址，一个公网地址（比如接口地址），都是端口映射情况

   object network ServerReal
        host 192.168.1.8
   object network R1Real
        host 192.168.1.1

   
   

   object service telnet
        service tcp destination eq telnet 
   object service ServerMapTelnet2321
        service tcp destination eq 2321 
   object service R1MapTelnet2322
        service tcp destination eq 2322

   
   nat (Outside,Inside) source dynamic any interface destination static interface ServerReal service ServerMapTelnet2321 telnet
   nat (Outside,Inside) source dynamic any interface destination static interface R1Real service R1MapTelnet2322 telnet

   
   

   access-list Outside extended permit tcp any object Serverreal eq telnet 
   access-list Outside extended permit tcp any object R1Real eq telnet 
   access-group Outside in interface Outside