一.概述： 默認情況下，不管是Inside還是DMZ區映射到Outside區的地址或服務，Inside和DMZ區都無法通過映射后地址來訪問內部服務器。ASA8.3版本之后有一種新的NAT叫Twice-NAT,它可以在一個NAT語句中既匹配源地址，又匹配目標地址，并且可以對源地址、目標地址，端口號，三個參數中一~三個參數的轉換。 二.基本思路：
A.Inside區映射到Outside區
①Outside區訪問Inside區映射后的地址沒有問題
②Inside區訪問Inside區映射后的地址，通過Twice NAT做源地址和目標地址轉換
---將源地址轉換為Inside接口地址，目標地址轉換為Inside設備實際地址
---如果不做源地址，因為訪問的數據流來回路徑不同，無法建立會話
③DMZ區訪問Inside區映射后的地址，通過Twice NAT做目標地址轉換
---將目標地址轉換為Inside設備的實際地址
---因為兩邊都是實際地址，因此需要Inside和DMZ互相有對方的路由
---也可以同時做源地址轉換，將源地址轉換為Iniside接口地址，為了便于審計，不建議這樣做
B.DMZ區映射到Outside區
①Outside區訪問DMZ區映射后的地址沒有問題
②Inside區訪問DMZ區映射后的地址，通過Twice NAT做目標地址轉換
---將目標地址轉換為DMZ區設備的實際地址
---因為兩邊都是實際地址，因此需要Inside和DMZ互相有對方的路由
---也可以同時做源地址轉換，將源地址轉換為DMZ接口地址，為了便于審計，不建議這樣做
---實際用模擬器測試，卻發現不做源地址轉換，經常報 -- bad sequence number的錯誤
---想不來為什么會報序列號錯誤，即使用MPF設置set connection random-sequence-number disable，也只是緩解，還是會偶爾出現，覺得可能是模擬器的緣故
③DMZ區訪問DMZ區映射后的地址，通過Twice NAT做源地址和目標地址轉換
---將源地址轉換為DMZ接口地址，目標地址轉換為DMZ區設備實際地址
---如果不做源地址，因為訪問的數據流來回路徑不同，無法建立會話
三.測試拓撲：
R1-----SW--(Inside)----ASA---（Outside）----R4
| |
| |
R2 R3（DMZ)
四.測試需求：
A.將R2的TCP23端口映射到ASA的Outside接口的23端口上
----要求R1~R4都能通訪問ASA的Outside接口的23端口訪問到R2的23端口
B.將R3的TCP23端口映射到ASA的Outside接口的2323端口上
----要求R1~R4都能通訪問ASA的Outside接口的2323端口訪問到R3的23端口
五.基本配置：
A.R1：
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
no shut
ip route 0.0.0.0 0.0.0.0 10.1.1.10
B.R2
interface FastEthernet0/0
ip address 10.1.1.2 255.255.255.0
no shut
ip route 0.0.0.0 0.0.0.0 10.1.1.10
line vty 0 4
password cisco
login
C.ASA:
interface GigabitEthernet0
nameif Inside
security-level 100
ip address 10.1.1.10 255.255.255.0
no shut
interface GigabitEthernet1
nameif DMZ
security-level 50
ip address 192.168.1.10 255.255.255.0
no shut
interface GigabitEthernet2
nameif Outside
security-level 0 ip address 202.100.1.10 255.255.255.0
no shut
D.R3:
interface FastEthernet0/0
ip address 192.168.1.3 255.255.255.0
no shut
ip route 0.0.0.0 0.0.0.0 192.168.1.10line vty 0 4
password cisco
login
E.R4:
interface FastEthernet0/0
ip address 202.100.1.4 255.255.255.0
no shut
五.ASA的NAT及策略配置：
A.動態PAT允許Inside和DMZ區能訪問公網
object network Inside-NET
subnet 10.1.1.0 255.255.255.0
nat (Inside,Outside) dynamic interface
object network DMZ-NET
subnet 192.168.1.0 255.255.255.0 nat (DMZ,Outside) dynamic interface
B.靜態PAT將R2和R3映射出去：
object network Inside-R2
host 10.1.1.2
nat (Inside,Outside) static interface service tcp 23 23
object network DMZ-R3
host 192.168.1.3
nat (DMZ,Outside) static interface service tcp 23 2323
C.防火墻策略：
①開啟icmp審查：
policy-map global_policy
class inspection_default
inspect icmp
②Outside口放行策略：
access-list OUTSIDE extended permit tcp any object Inside-R2 eq telnet
access-list OUTSIDE extended permit tcp any object DMZ-R3 eq telnet
access-group OUTSIDE in interface Outside
③DMZ口放行策略：
access-list DMZ extended permit tcp any object Inside-R2 eq telnet
access-list DMZ extended permit icmp any any
access-list DMZ extended deny ip any object Inside-NET
access-list DMZ extended permit ip any any
access-group DMZ in interface DMZ
---備注：這里只是測試，實際除非必要，盡量不要放行DMZ到Inside的訪問，要放行也需要針對主機放行
D.測試：
①Inside區和DMZ區能訪問公網：
R1#PING 202.100.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 202.100.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/80/168 ms
R2#ping 202.100.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 202.100.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/67/156 ms
R3#ping 202.100.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 202.100.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/120/204 ms
②被映射后的端口只能被Outside區訪問：
R4#TELNET 202.100.1.10 23
Trying 202.100.1.10 ... Open
User Access Verification
Password:
R2>show users
Line User Host(s) Idle Location
0 con 0 idle 00:55:06
* 66 vty 0 idle 00:00:00 202.100.1.4
Interface User Mode Idle Peer Address
R2>
R4#TELNET 202.100.1.10 2323
Trying 202.100.1.10, 2323 ... Open
User Access Verification
Password:
R3>show users
Line User Host(s) Idle Location
0 con 0 idle 00:51:12
* 66 vty 0 idle 00:00:00 202.100.1.4
Interface User Mode Idle Peer Address
R3>
R1#telnet 202.100.1.10
Trying 202.100.1.10 ...
% Connection timed out; remote host not responding
六.ASA的Twice NAT配置：
A.使得Inside區訪問Inside區映射后的地址時，既做源地址轉換，又做目標地址轉換
①配置對象：
object network Public-R2
host 202.100.1.10
object service tcp23
service tcp destination eq telnet
②配置twice-NAT:
nat (Inside,Inside) source static any interface destination static Public-R2 Inside-R2 service tcp23 tcp23
③允許相同接口的訪問：
same-security-traffic permit intra-interface
---因為訪問時，既從Inside口進，又從Inside出，所以需要這條
④測試：
R1#telnet 202.100.1.10
Trying 202.100.1.10 ... Open
User Access Verification
Password:
R2>show users
Line User Host(s) Idle Location
0 con 0 idle 01:07:35
* 66 vty 0 idle 00:00:0010.1.1.10
Interface User Mode Idle Peer Address
R2>
R2#telnet 202.100.1.10
Trying 202.100.1.10 ... Open
User Access Verification
Password:
R2>show users
Line User Host(s) Idle Location
0 con 0 202.100.1.10 00:00:00
* 66 vty 0 idle 00:00:0010.1.1.10
Interface User Mode Idle Peer Address
B.使得Inside區訪問DMZ區映射后的地址時，只做目標地址轉換
①配置對象：
object network Public-R3
host 202.100.1.10
object network DMZ-R3
host 192.168.1.3
object service tcp2323
service tcp destination eq 2323
②配置twice-NAT:
nat (Inside,DMZ) source static any any destination static Public-R3 DMZ-R3 service tcp2323 tcp23
③測試：
R1#telnet 202.100.1.10 2323
Trying 202.100.1.10, 2323 ...
% Connection timed out; remote host not responding
R3#debug ip tcp packet port 23
TCP Packet debugging is on for port number 23
R3#
*Mar 1 13:18:25.648: tcp0: I LISTEN 10.1.1.1:17155 192.168.1.3:23 seq 1568429504
OPTS 4 SYN WIN 4128
*Mar 1 13:18:25.652: tcp0: O SYNRCVD 10.1.1.1:17155 192.168.1.3:23 seq 1603796811
OPTS 4 ACK 1568429505 SYN WIN 4128
*Mar 1 13:18:25.656: tcp0: I SYNRCVD 10.1.1.1:17155 192.168.1.3:23 seq 4193850862
OPTS 4 SYN WIN 4128
*Mar 1 13:18:25.660: tcp0: O SYNRCVD 10.1.1.1:17155 192.168.1.3:23 seq 1603796811
ACK 1568429505 WIN 4128
*Mar 1 13:18:25.660: TCP0: bad seg from 10.1.1.1 -- bad sequence number: port 23 seq 4193850862 ack 0 rcvnxt 1568429505 rcvwnd 4128 len 0
④解決方法：
---修改NAT，做源地址轉換
nat (Inside,DMZ) source static any interface destination static Public-R3 DMZ-R3 service tcp2323 tcp23
⑤再次測試：
R1#telnet 202.100.1.10 2323
Trying 202.100.1.10, 2323 ... Open
User Access Verification
Password:
R3>show users
Line User Host(s) Idle Location
0 con 0 idle 00:02:15
* 66 vty 0 idle 00:00:00 192.168.1.10
Interface User Mode Idle Peer Address
R3>
R2#telnet 202.100.1.10 2323
Trying 202.100.1.10, 2323 ... Open
User Access Verification
Password:
R3>show users
Line User Host(s) Idle Location
0 con 0 idle 00:03:13
66 vty 0 idle 00:00:58 192.168.1.10
* 67 vty 1 idle 00:00:00 192.168.1.10
Interface User Mode Idle Peer Address
R3>
C.使得DMZ區訪問Inside區映射后的地址時，只做目標地址轉換
①配置對象：
---前面已經定義
②配置twice-NAT:
nat (DMZ,Inside) source static any any destination static Public-R2 Inside-R2 service tcp23 tcp23
③測試：
R3#telnet 202.100.1.10
Trying 202.100.1.10 ... Open
User Access Verification
Password:
R2>show users
Line User Host(s) Idle Location
0 con 0 202.100.1.10 00:02:49
* 66 vty 0 idle 00:00:00192.168.1.3
Interface User Mode Idle Peer Address
R2>
D.使得DMZ區訪問DMZ區映射后的地址時，既做源地址轉換，又做目標地址轉換
①配置對象：
---前面已經定義
②配置twice-NAT:
nat (DMZ,DMZ) source static any interface destination static Public-R3 DMZ-R3 service tcp2323 tcp23
---前面已經配置:same-security-traffic permit intra-interface
④測試：
R3#telnet 202.100.1.10 2323
Trying 202.100.1.10, 2323 ... Open
User Access Verification
Password:
R3>show users
Line User Host(s) Idle Location
0 con 0 202.100.1.10 00:00:00
66 vty 0 idle 00:07:01 192.168.1.10
67 vty 1 idle 00:06:02 192.168.1.10
* 68 vty 2 idle 00:00:00 192.168.1.10
Interface User Mode Idle Peer Address
R3>
