Introduction to Access Lists

At initial level the role of an access list is just as a filter for a router that checks whether to pass the data or to block it. The Access lists examine the network data packets by using multiple features such as source address, destination address, protocols, and port numbers. The rules that are defined in the access lists are the parameters for the checking of data packet coming from the network whether it should be denied or permitted. To understand the phenomena an example is quoted, an entry in the access list is compared to the rules; if it specifies the rule then it is permitted to enter otherwise it is denied and dropped.

A few things should be kept in mind before using the access. The access list is just a series of rules that compare the data coming so that it follows the rules of our network and don’t cause any problem. If this list of rules is not applied to the router interface it is of no use and it can do nothing. First you create an access list and then you apply it to get the work done. Access lists can be used to control the inbound and out bound or both at one time. If you have created an access list and also applied it to the respective interface and you have possibly missed some of the rules. There is no problem you can edit the list and add new rules.

Initially the access list is very simple and easy to apply but ass you add up rules in it. It gets complex and it is difficult to handle it for a non experienced user. That may result in the collapse of. In a single access list there can be different rules for different filtering technique.