• Cisco Switches and Routers running the Internet Operating System (IOS) have many things in common. Configuring these devices of course, is a skill that is sharpened the more you touch the device. During this post,...

  • In ACLs – Part 1 we learned the basics of access lists, including the facts that ACLs: Are created in global config mode End with an implicit “deny any” (which can be overridden) Must be placed into service somewhere to have any effect Thus, the commands: Router#conf t Router(config)#access-list 3 deny 172.16.1.1 Router(config)#access-list 3 deny …   Read More

  • In Routing Tables part one, we covered the basic purpose of a routing table and how an end device or intermediate device such as a router or multilayer switch can route based off its table. We also viewed different routing tables and how they are used to find a given destination network. In this blog, …   Read More

  • Welcome back! This time, we’ll take a look at access control lists, often referred to as “access lists” or “ACLs” (sometimes pronounced “ackels”). In Cisco IOS, ACLs are used for many things, including but not limited to: Filtering data packets (“firewalling”) Controlling Telnet or SSH access to a router or switch Filtering routing protocols Specifying …   Read More

  • In VLSM – Part 1, we looked at a quick way to do VLSM. This time, we’ll look at some more VLSM exercises, as well as examples in which VLSM won’t solve the problem. Of...

  • Welcome back! In this installment, we’re going to examine VLSM (Variable-Length Subnet Masking, RFC 1878), and how to use the subnetting shortcuts to solve VLSM problems. I’m sure that it won’t surprise you to know that we’ll need the powers of two chart: n = 8 7 6 5 4 3 2 1 2n = …   Read More

  • In this, our final look at subnetting for now, we’ll examine more “find the subnet” problems, specifically those in which the subnet/host boundary lies within the second or third octets. Here is the powers of...

  • In the previous editions of “Subnetting Shortcuts”, we solved various types of problems involving subnet masks. This time, we’ll look at some more complex cases, specifically those in which the subnet/host boundary lies within the second or third octets. But first, because our lives would be incomplete without it, here is the powers of two …   Read More

  • This time, we’ll use the shortcuts to solve some different types of problem. Instead of “find the mask”, this time the challenge is to “find the subnet”. Ready? Here’s the first problem: given a host address of 192.168.1.100 and a subnet mask of “/27”, determine the host’s subnet, the legal range of host addresses on …   Read More

  • In “Part 3”, we solved a subnet masking problem using shortcuts. This time, we’ll use the shortcuts to solve some additional problems. Here’s the first problem: given an address space of 172.16.1.0/24, divide the network...