CCNA refined analysis of test sites – Access Control List
Access Control List used:
1, limit network traffic and improve network performance. For example, queue technology, not only limits the network traffic and reduced congestion
2, provides the means to control the flow of communication. For example, can use its control of a router through a network of traffic
3, provides network access as a basic means of security. For example, in the company, the Ministry of Finance to allow employees access to financial computer server refused to visit other parts of the financial server
4, the router interface, the decision to allow or deny certain traffic to be transmitted. For example, FTP can allow the flow of communications, and refused to TELNET communications traffic.
How it works:
ACL provisions in the two operations, all of the applications are around two to complete the operation: to allow refuse
Attention: ACL is the CISCO IOS in a section of the procedures for the importation of the administrator’s instructions, has its own implementation of the order, it is the execution of the order from top to bottom, the implementation of his trip to find the match, once the match is to stop looking for If not found at the end of the match, then the period of implementation of the code implied – discarded DENY. So write ACL, we must pay attention to the order.
For example: to refuse traffic from 172.16.1.0/24 to the following written in the form of ACL
Allow 172.16.0.0/18
Refused to 172.16.1.0/24
Allow 192.168.1.1/24
Refused to 172.16.3.0/24
Then the results will be expected to run counter to the tables I and II to change over, you see there is no problem:
Refused to 172.16.1.0/24
Allow 172.16.0.0/18
Allow 192.168.1.1/24
Refused to 172.16.3.0/24
172.16.3.0/24 found and the situation just like this table does not play a key role to the implementation of the table on the second match was found, the router will allow, and we demand the opposite, then we should be table Four of the location moved to the front
End this:
Refused to 172.16.1.0/24
Refused to 172.16.3.0/24
Allow 172.16.0.0/18
Allow 192.168.1.1/24
Can be found in the ACL configuration of a law: the more accurate the more the front of the table, and the more general items tables on the more after the place.