问题
网络调通后，保证网络是通畅的。同时也很可能出现未经授权的非法访问。企业网络既要解决连连通的问题，还要解决网络安全的问题。
配置标准ACL实现拒绝PC1（IP地址为192.168.1.1）对外问网络192.168.2.1的访问
方案
访问控制是网络安全防范和保护的主要策略，它的主要任务是保证网络资源不被非法使用和访问。它是保证网络安全最重要的核心策略之一。
访问控制列表（Access Control Lists,ACL）是应用在路由器接口的指令列表。这些指令列表用来告诉路由器哪能些数据包可以收、哪能数据包需要拒绝。至于数据包是被接收还是拒绝，可以由类似于源地址、目的地址、端口号等的特定指示条件来决定。
标准访问控制列表只能根据数据包的源IP地址决定是否允许通过。
步骤
1.在R1上配置接口IP
tarena-R1(config)#interface f0/0
tarena-R1(config-if)#ip address 192.168.1.254 255.255.255.0
tarena-R1(config-if)#no shutdown
tarena-R1(config-if)#interface f0/1
tarena-R1(config-if)#ip address 192.168.2.254 255.255.255.0
tarena-R1(config-if)#no shutdown
2.测试主机到192.168.2.1的连通性
在实施ACL之前先检查网络是否能够正常通信，因为没有任何限制，网络应该是处于连通状态。
PC1测试如下所示：PC>ipconfig
FastEthernet0 Connection:(default port)
Link-local IPv6 Address.........: FE80::2E0:F7FF:FED6:54CC
IP Address......................: 192.168.1.1
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.1.254
PC>ping 192.168.2.100
Pinging 192.168.2.100 with 32 bytes of data:
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Ping statistics for 192.168.2.1:
Packets: Sent = 4, Received = 2, Lost = 2 (50% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
PC2测试如下所示：PC>ipconfig
FastEthernet0 Connection:(default port)
Link-local IPv6 Address.........: FE80::2D0:BAFF:FE98:9E29
IP Address......................: 192.168.1.2
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.1.254
PC>ping 192.168.2.1
Pinging 192.168.2.1 with 32 bytes of data:
Reply from 192.168.2.1: bytes=32 time=2ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Reply from 192.168.2.1: bytes=32 time=0ms TTL=126
Ping statistics for 192.168.2.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 2ms, Average = 0ms
3.在R1上配置标准访问控制列表，并应用到Fa0/0端口
ACL的匹配规则中，最后有一条隐含拒绝全部。如果语句中全部是拒绝条目，那么最后必须存在允许语句，否则所有数据通信都将被拒绝。
tarena-R1(config)#access-list 1 deny host 192.168.1.1
tarena-R1(config)#access-list 1 permit 192.168.1.0 0.0.0.255
tarena-R1(config)#interface f0/0
tarena-R1(config-if)#ip access-group 1 in
4.分别在两台主机上测试到192.168.2.1的连通性
PC1测试如下所示：
PC>ipconfig
FastEthernet0 Connection:(default port)
Link-local IPv6 Address.........: FE80::2E0:F7FF:FED6:54CC
IP Address......................: 192.168.1.1
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.1.254
PC>ping 192.168.2.1
Pinging 192.168.2.1 with 32 bytes of data:
Reply from 192.168.1.254: Destination host unreachable.
Reply from 192.168.1.254: Destination host unreachable.
Reply from 192.168.1.254: Destination host unreachable.
Reply from 192.168.1.254: Destination host unreachable.
Ping statistics for 192.168.2.1:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
PC2测试如下所示：
PC>ipconfig
FastEthernet0 Connection:(default port)
Link-local IPv6 Address.........: FE80::207:ECFF:FE46:CAC0
IP Address......................: 192.168.1.2
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.1.254
PC>ping 192.168.2.1
Pinging 192.168.2.1 with 32 bytes of data:
Reply from 192.168.2.1: bytes=32 time=1ms TTL=127
Reply from 192.168.2.1: bytes=32 time=0ms TTL=127
Reply from 192.168.2.1: bytes=32 time=1ms TTL=127
Reply from 192.168.2.1: bytes=32 time=0ms TTL=127
Ping statistics for 192.168.2.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 1ms, Average = 0ms
结果显示PC2（IP地址为192.168.1.2）可以正常访问192.168.2.1，而PC1（IP地址为192.168.1.1）已经被192.168.1.254（R1）拒绝。
5.在R1上查看相关的ACL信息
tarena-R1#show ip access-lists
Standard IP access list 1
10 deny host 192.168.1.1 (4 match(es))
20 permit 192.168.1.0 0.0.0.255 (8 match(es)
