Cisco Router Access List Basics

Without the security of networks, many businesses and home users to be exposed to all the world could see and access. Network security is not 100% prevent unauthorized users from accessing your network, but it helps to limit the availability of a network from the outside world. Cisco devices have many tools for monitoring and prevention of security threats. One of the most current Cisco technologies for network security in use, the access control lists or simply access lists (ACLs). If companies depend on their network to generate income, are a potential security breach a major concern.

ACLs are implemented by the Cisco IOS software. define ACLs, used by some packages running on the network can be avoided. The rules on access lists are implemented typically used for a particular network or host access to another network or host limit. However ACL can be more specific in implementing what is called an extended access list. This type of ACL allows you to deny or allow traffic not only on the source or destination IP address in office, but also the type of data that is sent is based.

Extended ACL can study requires several parts of the packet header, all parameters before denying or allowing the market to be coordinated. Standard ACLs are easier to configure, but it is not possible to deny or allow information on specific requirements. Standard access lists, you can allow or deny traffic based on source address, or a network. When creating ACL remember that there is always implicitly deny the statement. This means that if a package is not any of the statements of your access list will be blocked by default. to come, you must configure the option, a statement on the standard ACL and the prospects of finding a message about extended ACL.

Packets can be filtered in various ways. You can filter packets as they will be an interface of the router before any routing decision. You can also filter packets before they leave the interface, after the routing decision is taken. Configurable ACL statements are read from top to bottom. Thus, if a packet matches an explanation before going to the ACL set, he stops and takes a decision on the transmission of this statement that based games. Therefore, the most important statements and specific at the beginning of the list should be made and you must make statements of the most critical to least critical.