• Binary ANDing: multiplication to two binary numbers with examples

    Binary ANDing is the process of performing multiplication to two binary numbers. In the decimal numbering system, ANDing is addition: 2 and 3 equals 5. In decimal, there are an infinite number of answers when ANDing two numbers together. However, in the binary numbering system, the AND function yields only two possible outcomes, based on four different combinations. These outcomes, or answers, can be displayed in what is known as a truth table:

  • Cisco: Console Error Messages

    You may see three types of console error messages when working in the Cisco CLI:

    • Ambiguous command
    • Incomplete command
    • Invalid input
  • Cisco: Resetting Switch Configuration

    In this article, we will provide a sequence of commands to reset the configuration of a Cisco router. So:

  • Cisco: Shortcuts for Entering Commands

    To enhance efficiency, Cisco IOS Software has some shortcuts for entering commands. Although these are great to use in the real world, when it comes time to take the CCNA 200-301 exam, make sure you know the full commands, not just the shortcuts.

  • Classes of IPv4 Addresses: brief explanation with example

    IPv4 addresses were originally divided into five different classes according to size. These classes are no longer officially used because concepts such as classless interdomain routing (CIDR) and the mere fact that no more addresses are left to hand out have made address classes a moot point. But the terminology still remains out there and many IT professionals learned using this system, so it is a good starting point for understanding networks and, ultimately, subnetting of networks.

  • ip subnet-zero: Cisco IOS command using with examples

    Historically, it was always recommended that a subnet of all 0s or a subnet of all 1s not be used. Therefore, the formula of 2N – 2 was used to calculate the number of valid subnets created. However, Cisco devices can use those subnets, as long as the command ip subnet-zero is in the configuration. This command is on by default in Cisco IOS Software Release 12.0 and later; if it was turned off for some reason, however, you can reenable it by using the following command:

  • IPv6 Address Types: unicast, multicast, and anycast

    In IPv6, there are three types of addresses: unicast, multicast, and anycast. This section gives a (very) high-level overview of these types.

  • IPv6: A Very Brief Introduction

    When IPv4 became a standard in 1980, its 32-bit address field created a theoretical maximum of approximately 4.29 billion addresses (232). IPv4 was originally conceived as an experiment, and not for a practical implementation, so 4.29 billion was considered to be an inexhaustible amount. But with the growth of the Internet, and the need for individuals and companies to require multiple addresses - your home PC, your cell phone, your tablet, your PC at work/school, your Internet-aware appliances - you can see that something larger than 32-bit address fields would be required. In 1993, the Internet Engineering Task Force (IETF) formed a working group called the IP Next Generation working group.

  • IPV6: Prefix Length Notation

    In IPv4, the prefix of the address (the network portion) can be represented either by a dotted-decimal netmask (the subnet mask) or through CIDR notation. When we see or, we know that the network portion of the address is the first 24 bits of the address (192.168.100) and that the last 8 bits (.0) are host bits. IPv6 address prefixes are represented in much the same way as IPv4 address prefixes are written in CIDR notation. IPv6 prefixes are represented using the following format:

  • IT Industry Trends and Transitions: network availability & security

    We’ll start with why you even considered ACI in the first place. Industry changes are impacting almost every aspect of IT. Applications are changing immensely, and we’re seeing their lifecycles being broken into smaller and smaller windows as the applications themselves are becoming less structured. What the network used to control and secure has changed greatly with virtualization via hypervisors. With containers and microservices being deployed more readily, we’re seeing change happen at a much faster pace.

  • Network and Cloud

    books on network and cloud technologies

    This section publishes links to books on network and cloud technologies: the theory and practice of networking, network protocols, routers and telecommunications equipment, architecture and cloud technologies.

    Share books, links, read reviews. Express your opinion and give recommendations to other members of our social network for programmers.

  • Network and subnetwork masks and Ways to write them

    Because IPv4 addresses are hierarchical, there needs to be some way of distinguishing between the network portion of the address and the host portion. To accomplish this, an IPv4 address must be paired with a network mask, which is also sometimes called a subnetwork mask or simply a subnet mask or mask. A network mask is a 32-bit string of binary characters that defines which portion of the address represents the network and which portion of the address represents the specific host.

  • Network, Node and Broadcast Addresses: brief explanation

    When IPv4 addressing was first designed, there needed to be a way for devices and people to recognize whether an address referred to a specific device or to a group of devices. Some rules were created to help determine the difference between a network address and a node (or host) address:

  • Networking, Cloud Computing and virtualization

    Our social network IT professionals blogs on the topic of Network Technologies and Cloud Computing. Setting up local and global networks. Trends, prospects, approaches. Routing, Internet, cloud services, etc. Programming and administration.

  • Reducing the Notation of an IPv6 Address

    Looking at the longest representation of an IPv6 address can be overwhelming:

  • Steps to create an IP plan using VLSM by example

    You follow the same steps in performing VLSM as you did when performing classical subnetting.


    Throughout this blog, I use serial links between routers to help differentiate these networks from Ethernet networks where hosts usually reside. In today’s more modern networks, Ethernet links are used almost exclusively between routers, and serial links are rapidly becoming obsolete. However, using serial links is a very cost-effective way to set up a testing lab for learning purposes; I have seen home labs, school labs, and corporate training labs use serial links for this reason. Even though a simple Ethernet link (10 Mbps) is faster than a serial link (1.544 Mbps), I use serial links in all of my Portable Command Guides to show the difference between an Ethernet link and a point-to-point link to another router.

  • Subnetting a Class B Network Using Binary

    You have an address of /16. You need nine subnets. What is the IP plan of network numbers, broadcast numbers, and valid host numbers? What is the subnet mask needed for this plan?

  • Subnetting a Class C Network Using Binary

    You have an address of /24. You need nine subnets. What is the IP plan of network numbers, broadcast numbers, and valid host numbers? What is the subnet mask needed for this plan?

  • Understanding Route Summarization: Basic concepts with example

    Route summarization, or supernetting, is needed to reduce the number of routes that a router advertises to its neighbor. Remember that for every route you advertise, the size of your update grows. It has been said that if there were no route summarization, the Internet backbone would have collapsed from the sheer size of its own routing tables back in 1997!

  • Using Cables and Connections to Cisco router or switch

    This chapter provides information and commands concerning the following topics:

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