Basic NAT<基本NAT>：
配置BASIC NAT，实现一个私网地址通过一个公网地址转换访问INETERNET:
[RTA]int e0/0
[RTA-Ethernet0/0]ip add 10.0.0.254 24
[RTA-Ethernet0/0]undo shutdown
[RTA-Ethernet0/1]int e0/1
[RTA-Ethernet0/1]ip add 198.76.28.1 24
[RTA-Ethernet0/1]undo shutdown
[RTA]rip
[RTA-rip-1]ver 2
[RTA-rip-1]undo summ
[RTA-rip-1]undo summary
[RTA-rip-1]network 198.76.28.0
[RTA]int e0/0
[RTA-Ethernet0/0]ip add 198.76.28.2 24
[RTA-Ethernet0/0]undo shutdown
[RTA-Ethernet0/1]int e0/1
[RTA-Ethernet0/1]ip add 198.76.29.1 24
[RTA-Ethernet0/1]undo shutdown
[RTA]rip
[RTA-rip-1]ver 2
[RTA-rip-1]undo summ
[RTA-rip-1]undo summary
[RTA-rip-1]network 198.76.28.0
[RTA-rip-1]network 198.76.29.0
PCA:10.0.0.1 255.255.255.0 GT:10.0.0.254
PCB:10.0.0.2 255.255.255.0 GT:10.0.0.254
SERVER:198.76.29.4 255.255.255.0 GT:198.76.29.1
此时公网网络已经正常访问，私网无法访问公网server：
[RTA]ping 198.76.29.4
PING 198.76.29.4: 56 data bytes, press CTRL_C to break
Request time out
Reply from 198.76.29.4: bytes=56 Sequence=2 ttl=255 time=1 ms
Reply from 198.76.29.4: bytes=56 Sequence=3 ttl=255 time=1 ms
Reply from 198.76.29.4: bytes=56 Sequence=4 ttl=255 time=15 ms
Reply from 198.76.29.4: bytes=56 Sequence=5 ttl=255 time=10 ms
--- 198.76.29.4 ping statistics ---
5 packet(s) transmitted
4 packet(s) received
20.00% packet loss
round-trip min/avg/max = 1/6/15 ms
C:\Documents and Settings\xiaofei>ping 198.76.29.4
Pinging 198.76.29.4 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 198.76.29.4:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
私网10.0.0.0网段需要访问公网server就需要使用basic nat进行地址转换：
[RTA]firewall enable
[RTA]firewall default permit
[RTA]acl number 2000
[RTA-acl-basic-2000]rule 0 permit source 10.0.0.0 0.0.0.255 定义基本ACL允许私网可以访问的网段。
[RTA-acl-basic-2000]quit
[RTA]nat address-group 1 198.76.28.10 198.76.28.20 创建BASIC NAT公网地址池
[RTA]int e0/0/0
[RTA-Ethernet0/0/0]nat outbound 2000 address-group 1 no-pat 在接口绑定ACL规则和地址池，NO-PAT表示不使用NAPT.
此时的私网网段可以成功访问公网的server：
C:\Documents and Settings\xiaofei>ping 198.76.29.4
Pinging 198.76.29.4 with 32 bytes of data:
Reply from 198.76.29.4: bytes=32 time=1ms TTL=254
Reply from 198.76.29.4: bytes=32 time=2ms TTL=254
Reply from 198.76.29.4: bytes=32 time=15ms TTL=254
Reply from 198.76.29.4: bytes=32 time=16ms TTL=254
Ping statistics for 198.76.29.4:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 1ms, Maximum = 16ms, Average = 8ms
在NAT表中可以看出，每个私网地址通过一个公网地址一个端口进行转换来访问公网server：
[RTA]disp nat session
There are currently 6 NAT sessions:
Protocol GlobalAddr Port InsideAddr Port DestAddr Port
1 198.76.28.10 512 10.0.0.1 512 198.76.29.4 512
×××: 0, status: NOPAT, TTL: 00:01:00, Left: 00:01:00
1 198.76.28.12 512 10.0.0.2 512 198.76.29.4 512
×××: 0, status: NOPAT, TTL: 00:01:00, Left: 00:00:08
