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一.测试拓扑：
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二.基本思路和笔试题目：
A.基本思路：
通过使用NAT extendable参数，使得内部一个地址能在不同接口以不同地址NAT出去，否则内部一个地址只能配静态NAT一次。
B.笔试题目：
An internal DNS server requires a NAT on a Cisco IOS router that is dual-homed to separate ISPs using distinct CIDR blocks. Which NAT capability is required to allow hosts in each CIDR block to contact the DNS server via one translated address?
答案：NAT extendable
三.基本配置：
A.R1路由器：
interface Ethernet0/0
ip address 202.100.1.2 255.255.255.0
no shut
B.R2路由器：
interface Ethernet0/0
ip address 61.1.1.2 255.255.255.0
no shut
C.R3路由器：
interface Ethernet0/0
ip address 10.1.1.1 255.255.255.0
ip nat inside
no shut
interface Ethernet0/1
ip address 202.100.1.1 255.255.255.0
ip nat outside
no shut
interface Ethernet0/2
ip address 61.128.1.1 255.255.255.0
ip nat outside
no shut
D.R4路由器
interface Ethernet0/0
ip address 10.1.1.2 255.255.255.0
sno shut
ip route 0.0.0.0 0.0.0.0 10.1.1.1
line vty 0 5
password cisco
login
四.NAT extendable配置：
A.R3路由器：
ip nat inside source static 10.1.1.2 61.128.1.8 extendable
ip nat inside source static 10.1.1.2 202.100.1.8 extendable
B.测试：
R1#telnet 202.100.1.8
Trying 202.100.1.8 ... Open
User Access Verification
Password:
R4>show users
Line User Host(s) Idle Location
0 con 0 idle 06:08:16
*130 vty 0 idle 00:00:00 202.100.1.2
Interface User Mode Idle Peer Address
R2#telnet 61.128.1.8
Trying 61.128.1.8 ... Open
User Access Verification
Password:
R4>show users
Line User Host(s) Idle Location
0 con 0 idle 06:09:06
130 vty 0 idle 00:00:49 202.100.1.2
*131 vty 1 idle 00:00:00 61.128.1.2
Interface User Mode Idle Peer Address