The use of the ‘established’ keyword in Cisco IOS Access Control Lists (ACLs)

So you are looking over your Access Control Entries (ACEs) in your Access Control List (ACL) when you notice the use of the ‘established’ keyword at the end of an entry. In fact, you also notice that the from and to values seem to be reversed. Check out this video tutorial on the use of the ‘established’ keyword where we take a deep dive look at just how it works, why it only allows Transmission Control Protocol (TCP) packets with the ACK or RST flags set and how you can use this to secure your Cisco environment. Enjoy!