Without network security, many businesses and residential users alike would be exposed for all you world to see and access. Network security doesn’t 100% prevent unauthorized users from entering your network but it helps limit a network’s availability on the surface world. Cisco devices have several tools to help monitor preventing security threats. One of the most common technologies found in Cisco network security are Access Control Lists or perhaps Access Lists (ACLs). When businesses depend on their network to generate income, potential security breaches turn into a huge concern.

ACL’s are implemented through Cisco IOS Software. ACL’s define rules which you can use in order to avoid some packets from flowing over the network. The rules implemented on access-lists are usually accustomed to limit a specific network or host from accessing another network or host. However ACL’s may become more granular by implementing what is known as an extended access-list. Such a ACL permits you to deny or permit traffic based not only on source or destination Ip, and also depending on the type data that’s being sent.



Extended ACL’s can examine multiple elements of the packet headers, requiring that most the parameters be matched before denying or allowing the traffic. Standard ACL’s are simpler to configure such as the enable you to deny or permit information based on more specific requirements. Standard Access-Lists only permit you to permit or deny traffic using the source address or network. When making ACL’s do not forget that there is always an implicit deny statement. Which means if your packet does not match all of your access list statements, it’s going to be blocked by default. To over come this you must configure the permit any statement on Standard ACL’s as well as the permit any any statement on Extended ACL’s.

Packets may be filtered often. You are able to filter packets as they enter a router’s interface before any routing decision is created. It’s also possible to filter packets before they exit an interface, following your routing decision is done. Configured ACL’s statements are always read throughout. Therefore if a packet matches an argument before going through the whole ACL, it stops and is really a forwarding decision according to that statement which it matches. And so the most important and specific statements should be made at the outset of your list and you need to create statements beginning from one of the most essential to the least critical.

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