Computer networks

With this article, which just summarizes the general basics about computer networks, I would like to start a series of articles about the basics of computer networks, or networking. In this article you will find a brief description of the term computer network and the basic divisions of networks.

In the second part of the description of basic terms and functions of computer networks, I briefly discuss network topologies. A network topology describes the arrangement of network elements, whether physical or logical. The basic topologies used in local area networks (LANs) are bus, star, and ring.

The third part of the series on computer networks. The OSI model is the established term for the Open Systems Interconnection Basic Reference Model. It is an abstract description of network communication and the protocols used for communication between computers, which is divided into seven layers. In communication, encapsulation is performed - encapsulate on the sender side and unpack on the receiver side. It starts with layer 7, which is encapsulated in layer 6, and so on. This model was created to standardize communication so that hardware and software from different vendors could communicate with each other.

The fourth part of the description of basic terms of computer networks is devoted to the most used network technology (mainly in LAN) Ethernet. It also describes the related terms collision domain and duplex (half and full). If you're looking for a third part, it's a description of the ISO/OSI model that I posted earlier.

In the fifth part of the series on computer networks, I briefly summarize basic information about the most widely used TCP/IP protocol. The TCP/IP model and the principle of encapsulation when sending data are mentioned here. I am trying to describe the differences between the common terms packet and frame. And finally the frame format is displayed.

The sixth part of the basics of computer networks is devoted to transmitting methods (I don't know if this is the most appropriate label). Broadcast, unicast and multicast transmission in the network is briefly described here.

The seventh part of the series on computer networks is more interesting and provides practical information. At the beginning there is a description of the basic terms for networks and subnets, IP addresses and masks. Next, the various network classes and how to write subnets are discussed. The second part deals with practical calculations of network ranges, network masks, number of hosts and subnets.

The eighth part of the series on computer networks. VLAN, or Virtual Local Area Network, is a common technology these days that brings a number of advantages. I think that all medium-sized and larger companies use VLAN technology, and it can be interesting for small companies as well. VLANs are used to logically divide the network without being tied to physical division. In the article, I try to describe everything necessary to understand what VLAN is, what are the advantages and methods of deployment.

The ninth part of the series on computer networks is again short and concise. It briefly describes how the TCP protocol establishes and terminates connections.

In the tenth part of the series on computer networks, I will focus on the ways in which data (frames) are delivered (and addressed) on the network. I am considering ethernet (and therefore frame and physical addressing) and TCP/IP (packet and logical addressing). In practice, this is either direct delivery or indirect delivery. Everything also depends on the active (passive) elements used, so I describe three common examples (shared medium, switch, router). In the second part of the article, there is a brief description of active network elements and the principles of their function.

In the eleventh part of the series on computer networks, I deal with routing, i.e. routing in networks. There is a brief description, explanation of terms, and then some more common routing methods (RIP, IGRP, EIGRP and OSPF) are described very briefly, including the division of these methods. For the methods, there is a sample of the basic configuration on Cisco. The article is far from exhaustive and the description is often to the point. Finally, rooting on Windows is mentioned.

So far, the last twelfth part of the series on computer networks is briefly devoted to the ARP protocol. This is an important protocol that is used to find the MAC address of a station that has a certain IP address. Because we need MAC addresses for every communication, ARP is used very often.

This article concludes the series on computer networks. Some parts of the series have dealt with simple and familiar things, others with something more complex. I did not try to go into complete details in the description, but rather to give a global view of the subject, and if someone needs a more detailed description, he can simply find the necessary materials on the Internet by keywords. This article summarizes the references to the previous parts and simply describes the links and continuities of the chapters.

This article is thematically related to the series on the basics of computer networks, but is written in a different form. I was inspired to write this article by Microsoft certification tests, which very often contain questions focused on DNS, especially the use of different zone types. So the first part is a sort of theoretical and practical description of DNS functionality, which is by no means exhaustive. And the second part deals with the various uses of DNS as presented by Microsoft. This includes things that I've never used in practice, but are needed for tests.

Almost everyone has an idea of ​​what Wake on LAN is, i.e. remote turning on (waking) of the computer. But when I started thinking about using WOL on a computer that is in a different subnet and therefore has a router in between, I realized a number of complications. I have studied a number of articles and discussions and found that most of the time the description is incomplete and often even wrong. Therefore, in this article I comprehensively summarize the entire issue that I have studied. I am describing a solution for waking up a computer in the same but also a remote (perhaps via the Internet) subnet. And I am also providing an example script in PHP.

Internet Protocol (IP) is used for data communication in switched computer networks that use TCP/IP. It is the most widely used protocol on the Internet and on LANs. The first major version is now referred to as IPv4 and is still the majority version in use. Its main disadvantage is that addresses are 32 bits in size. Therefore, a new version of IPv6 has been created, which brings a number of advantages, but the main difference is that the addresses are 128 bits large. IPv6 is now being deployed globally.

Multicast is a method of efficiently communicating from one sender to multiple receivers. An example is Internet radio (and by comparison, regular radio), where there is one source and many receivers receiving the same data at the same time. In practice, this is often handled by making individual connections for each receiver. So the server is heavily loaded and part of the network infrastructure is unnecessarily overloaded with the transmission of duplicate data. With multicast, we deliver information simultaneously to a group of recipients in the most efficient way so that the message travels only once through each network node, with copies being made only when the paths to the recipients are split. This paper explains the general principle of multicast and then discusses the Internet Group Management Protocol (IGMP) and the Protocol Independent Multicast (PIM) routing protocol in all its variants.

This article only summarizes basic information about the most common types of attacks on switches. The information it provides can be found in many places, so I am including it here for completeness. MAC flooding, ARP spoofing, VLAN hopping attacks are described and methods to defend against them on Cisco switches are mentioned. A defense method called Dynamic ARP Inspection is also discussed.

When a router or L3 switch is forwarding packets (routing), it uses one of the methods called Router Switching Path, which determines how fast it can work. Some of these methods are Process Switching, Fast Switching, and Cisco Express Forwarding. The article briefly mentions these methods and also describes related terms such as CAM table, FIB, ARP, as well as switch, MLS and router. Some of these terms are described in more detail in earlier articles.

We will probably not design and implement a larger computer network on our own, but will entrust it to a specialized company. Nevertheless, it is good to have at least a basic overview of this area and ideally detailed knowledge so that the resulting network corresponds to our ideas and not to the view of the implementer. So let's look at the areas and issues we need to consider when designing a network.

NLB is used for what the name says, load balancing on multiple servers, in other words, creating a cluster. The whole principle is quite simple. The advantage (but there are also disadvantages) is that it is a software solution and we can do without HW load balancer. We won't go into the actual configuration of the NLB here (which is quite trivial using the wizard, by the way), but how the NLB behaves in the network (specially with Cisco elements).

In the article, we will look at the types of cables used for LAN telecommunication networks (not only local networks, but also more extensive types of Ethernet networks) and data (storage) SAN networks. The same transmission media, cabling and connectors are used for both types of networks. We will focus on metallic and optical media (cables).

We will follow up on the previous article, which described the types of cables used for LAN telecommunication networks and data (storage) SAN networks, and describe the used connectors, Transceivers (converters) and Direct Attach (direct connecting) cables. We will again focus on metallic media (twisted pair) and optical media (optical fiber).

DNSSEC is used to secure DNS records from spoofing by using a digital signature and chain of trust. When we use DNSSEC on a domain (DNS zone), we sign all DNS source records. This allows DNS Resolver to check that the record is from its owner and has not been modified. This article attempts to (briefly) describe the principle of DNSSEC and related technologies.

DNSSEC is used to secure DNS records from being spoofed. On Windows Server, we can install the DNS Server role and run an Authoritative Name Server, which manages a specific domain (zone), or a Recursive Name Server, which is used to look up the answer to a client's DNS query. In both cases, DNSSEC is supported. In this article, we will describe how DNSSEC is used on Microsoft DNS Server. We will focus on public domain signing on the Internet, but we will also mention other uses.

When sending messages using SMTP between mail servers, TLS encryption is already heavily used. By default, mail servers do not check the validity of the certificate used. The indication that they support encryption is sent in clear text in the protocol. DNS-based Authentication of Named Entities can be used for security. We publish a special TLSA record in DNS that says that a particular service supports encryption and what certificate it uses.