演習で学ぶネットワーク

What is IS-IS

What is IS-IS IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol. Another link state routing protocol is OSPF. IS-IS was originally developed for routing over CLNS (Connectionless Network Servi

2022/09/29 23:23

What is BGP

What is BGP BGP is EGP (Exterior Gateway Protocol). A routing protocol that allows routing information to be exchanged between different autonomous systems (AS). BGP leaves the routing within the AS to the IGP. BGP starte

2022/09/29 23:19

What is an AS (Autonomous System)?

What is an AS (Autonomous System)? The Internet is vast and contains numerous networks. In order to deliver data to destinations all over the world, it is necessary to manage routing information for all networks on the Internet.

2022/09/29 23:15

What is OSPF

Features of OSPF OSPF is a link-state routing protocol standardized by the IETF. Unlike EIGRP, which was originally developed by Cisco, routing is possible between multi-vendor routers other than Cisco routers. One of the maj

2022/09/29 23:11

What is Multihoming?

What is multihomingMulti-homing is a function that can distribute the load over multiple routes to the same destination. You can connect to multiple ISPs at the same time and distribute packets according to the line speed to each I

2022/09/28 23:32

What is HSRP?

HSRP とは デフォルトゲートウェイを失うと、そのデフォルトゲートウェイに接続しているセグメント上の機器は通信できなくなってしまいます。このような障害を回避するための対策としてデフォルトゲートウェイを二重化するという方法があります。 ルータBを増設して、下の図のようにネットワークを構成しなおしたとします。しかし、セグメントAに所属するPCのデフォルトゲートウェイをRouterBに設定しなおさなければなりません。 デフォルトゲートウェ

2022/09/28 23:30

What is Fast Ether Channel?

What is Fast Ether Channel? Fast Ether Channel (FEC) is a Cisco proprietary standard that other vendors call Trunk or Link Aggregation. Gigabit Ethernet Ether Channel (GEC) functionality is also available on switches with Gigabit-

2022/09/28 23:27

What is STP/Spanning Tree Protocol?

What is STP/Spanning Tree Protocol? When configuring a network, the network may be looped to ensure redundancy. However, in such a configuration, broadcasts and all kinds of communication data will circulate forever on the configu

2022/09/28 23:25

VLANs (trunk tagging)

VLAN (trunk tagging)What if I want to create a VLAN that spans multiple switches?For example, consider creating VLAN10, VLAN20, and VLAN30 on two switches.If no trunk port is set, the network configuration will be as shown in t

2022/09/28 23:21

What is VLAN (virtual LAN)?

What is a VLAN (virtual LAN)? Intelligent switches can use VLANs. Even if you say VLAN (virtual LAN), for those who are unfamiliar with this word, I think that it is difficult to understand the image of VLAN.It may be easier t

2022/09/28 23:18

Useful Network Tools

Useful Network ToolsPacket capture (Wireshark) Ethereal, a classic packet analysis software, has become an open source project and has been renamed to Wireshark. Although it is free software, it has a lot of functions. It

2022/09/28 02:09

TFTP server

TFTP serverTFTPD64 There are some TFTP software that can be used for free, but "TFTPD64" is a TFTP server free software that can be easily operated on Windows 10 with a GUI.It can be used simply by setting the "current director

2022/09/28 02:03

terminal emulator

terminal emulatorTera TermA standard terminal emulator.It is open source and supports SSH2 protocol and UTF-8 display.Telnet, SSH and console connections are supported.Supports serial port connection (PC communication).

2022/09/28 01:57

Building a LAN with power line communication (PLC)

What is public key cryptography?In public key cryptography, a pair of keys, a private key and a public key, is created for each user. A private key is a key that is private to you and that you create and keep private until you no l

2022/09/28 01:52

Build a network at home (appliances and game consoles)

Connecting a digital high-definition LCD TV In order to enjoy viewer-participation-type programs on digital TV broadcast interactive services, it is necessary to be connected to the Internet. The settings are easy, so connect to t

2022/09/28 01:48

Build a network at home (DHCP/IP acquisition)

Setting up a DHCP server/PC network settings We live in an age when each individual owns a personal computer, not just one per household. Nowadays, more people use smartphones and tablets than computers. It has become commonp

2022/09/28 01:45

What is VRRP?

What is VRRP?VRRP is an abbreviation for "Virtual Router Redundancy Protocol" and is a protocol that supports router redundancy on the network. Also known as Virtual Router Redundancy Protocol, it allows for high availability and r

2022/09/28 00:49

QoS/Packet Identification

QoS/packet identification QoS functions can be broadly divided into three functions: "packet identification," "priority control," and "bandwidth control." These functions are used to operate.So far, we have explained “priority cont

2022/09/28 00:47

QoS/bandwidth control

QoS/bandwidth controlBandwidth control refers to technology that allocates or limits bandwidth for each type of packet. By using CQ explained in priority control, it is possible to allocate bandwidth according to packet weight.&nbs

2022/09/28 00:44

QoS/priority control mechanism/PQ+WFQ

QoS/priority control mechanism/PQ+WFQ So far, PQ and CQ have been introduced, but there are also methods that achieve QoS with more complicated processing. The processing method is a method that combines a method that divides queu

2022/09/28 00:42

VLSM and Route Aggregation

VLSM and Route AggregationVLSM and route summarization With the spread of the Internet, the number of network routes around the world has increased dramatically. Therefore, routers have to learn a huge amount of route informat

2022/09/27 02:45

VLSM and classful routing

VLSM and classful routingVLSM and classful routing protocols Routing protocols include classful routing protocols that do not support VLSM and classless routing protocols that support VLSM.Classful routing protocol: RIPv1, IGRP

2022/09/27 02:33

How to divide subnets in VLSM

How to divide subnets in VLSM In the network shown below, we will explain how to divide the "192.168.1.0/24" network into subnets and assign IP addresses.The largest network in the diagram above is a network with 60 hosts.

2022/09/27 02:30

What is a Variable Length Subnet Mask (VLSM)

What is a Variable Length Subnet Mask (VLSM)Limitations of fixed-length subnetting Subnetting, which divides networks, is inflexible in large networks. With simple subnet division, all the divided subnets have an equal size, s

2022/09/27 02:04

FTP communication (active mode/passive mode)

FTP communication (active mode/passive mode)FTP communication (active mode) FTP communication has PORT mode (active mode) and PASV mode (passive mode). Here, we will explain the active mode.Active mode is the default trans

2022/09/27 01:57

FTP/TFTP communication

FTP/TFTP communication FTP stands for "File Transfer Protocol" and is also known as File Transfer Protocol. It is a communication protocol for transferring files over a network, and has been the most commonly used file transfer pr

2022/09/27 01:53

Packet flow in DHCP

Packet flow in DHCPPacket flow in DHCP relay Here, we will use a diagram to explain the flow of packets in exchanges between the DHCP client and DHCP server when DHCP relay is performed.The communication between DHCP client and

2022/09/27 01:50

Contents of DHCP message

Contents of DHCP messageHere, we will explain the contents of each frame of DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK. If the DHCP client and server are on the same network, the interaction between the DHCP client and DHCP

2022/09/27 01:48

BOOTP/DHCP message format

BOOTP/DHCP message format Here, I will explain the message format of DHCP. Since DHCP is upward compatible with BOOTP (Bootstrap), the structure of the messages has remained largely unchanged.First, I will explain the BOOTP me

2022/09/27 01:45

UDP broadcast relay for DHCP

Effects of UDP broadcastsThe DHCP relay agent function can be used to relay DHCP UDP broadcast requests. When a router receives a DHCP request (broadcast), it unicasts the DHCP request to a DHCP server on another network. H

2022/09/27 01:42

Build a network at home (wireless router settings)

Building a network at home (wireless router settings) Setting up a router can be a bit difficult for beginners. A long time ago, you had to enter a setting command or set the IP address of the same network address on your computer

2022/09/26 00:13

Build a network at home (repeater)

Build a network at home (repeater) Due to the influence of the new coronavirus, remote work and online classes are becoming popular, and the need for a home network is increasing. Among them, wireless LAN is convenient because it

2022/09/26 00:10

Build a network at home (install a wireless router)

About the installation location Regarding the installation location of the wireless broadband router (hereafter referred to as wireless router), if it is an FTTH line, it will be near the entrance of the optical fiber cable. It is

2022/09/26 00:09

Build a network at home

build a network at home Broadband connections such as FTTH (optical fiber) are now the norm for home Internet connections. In addition, we have entered an era in which not only personal computers but also smartphones and tablets a

2022/09/26 00:07

POP before SMTP/APOP before SMTP

Email authentication (POPS before SMTPS)In APOP before SMTP, the password used for authentication was encrypted, but the email text was not encrypted. Although the risk of passwords being intercepted and the SMTP server becoming a

2022/09/25 22:09

E-mail (restricted by domain, linked with blacklist)

Email (restrict by domain) In e-mail, the part after @ represents the domain name. By specifying this domain name, you can block emails with that domain name in the email address. For example, if you specify and restrict the d

2022/09/25 22:07

E-mail (S/MIME and PGP) and mail relay problems

Email (S/MIME and PGP) S/MIME (Secure/Multipurpose Internet Mail Extensions) and PGP (Pretty Good Privacy) are commonly used for email encryption and electronic signatures.S/MIME is pronounced as "esmime" and PGP is pronounced as "

2022/09/25 22:05

Public Key Cryptosystem

What is public key cryptography?In public key cryptography, a pair of keys, a private key and a public key, is created for each user. A private key is a key that is private to you and that you create and keep private until you no l

2022/09/25 22:03

Common Key Cryptosystem

What is public key cryptography?In public key cryptography, a pair of keys, a private key and a public key, is created for each user. A private key is a key that is private to you and that you create and keep private until you no l

2022/09/25 21:59

What is MIME? E-mail encryption and electronic signature

What is MIME Although e-mail is now a service that everyone uses, e-mail itself has a long history, dating back to the early days of the Internet. Since the system was originally born in the English-speaking world, it is assume

2022/09/25 21:57

NFS

NFS The NFS (Network File System) service is a service developed by Sun Microsystems for accessing files on a network. The NFS service typically uses UDP or TCP port 2049. By using this service, you can access the file system

2022/09/25 01:04

BOOTP

What is BOOTPBOOTP (Bootstrap Protocol) is a protocol for configuring hosts that was developed before DHCP.BOOTP is defined in RFC 951 of 1985. DHCP is an improvement over BOOTP, addressing the limitations of BOOTP as a service

2022/09/25 00:59

Problems of DHCP ・DHCP function of network equipment

Problems of DHCP ・DHCP function of network equipment DHCP is a convenient protocol that automatically distributes network configuration information such as IP addresses, but the following points should be noted.◆ Do not use for ser

2022/09/25 00:57

DHCP (segment identification/message)

DHCP (segment identification) By using the DHCP relay function, you can build a network as shown in the figure below. DHCP servers can be aggregated and managed by a single DHCP server.Set a scope for each segment (network

2022/09/25 00:53

DHCP relay agent

DHCP relay agent Routers block broadcasts instead of forwarding them, so messages cannot reach DHCP servers beyond the router.To solve this problem, you need to relay DHCP broadcast requests. The function that receives this

2022/09/25 00:51

DHCP server deployment

Problem with multiple DHCP servers on the same segment If the network is configured to obtain IP addresses automatically, if there is only one DHCP server, the DHCP server will be a single point of failure, and if the DHCP server goes

2022/09/25 00:49

DHCP (Gratuitous ARP)

DHCP (Gratuitous ARP)Here, I will explain the relationship between Gratuitous ARP and DHCP. Gratuitous ARP is a type of ARP packet that is mainly used to check if the same IP address has already been assigned to another host when a

2022/09/25 00:47

DHCP (operation, lease renewal and release, command)

DHCP behaviorThe flow of DHCP operation is shown in the figure below.1. DHCP DiscoverThe client broadcasts "255.255.255.255" and requests to be assigned an IP address.2. DHCP offers The DHCP server receive

2022/09/25 00:45

What is DHCP

What is DHCP DHCP is an abbreviation for "Dynamic Host Configuration Protocol", a protocol that automatically assigns information necessary for computers to connect to networks.The following information can be set automatically usi

2022/09/25 00:43

TFTP

What is TFTP TFTP stands for "Trivial File Transfer Protocol" and is defined in RFC 1350. "Trivial" means "insignificant", and you can see from the name that it is a protocol that is not as good as FTP. TFTP is a protocol that

2022/09/25 00:40

IEEE802.11b/IEEE802.11g channels

IEEE802.11b/IEEE802.11g channels The IEEE802.11b standard is compatible with the existing IEEE802.11 standard. The wireless frequency uses the 2.4 GHz band, and the transmission speed can be increased from 2 Mbps to a theoretical

2022/09/23 12:57

Wireless LAN (what is a channel)

Wireless LAN (what is a channel) Wireless LAN divides the frequency band used so that multiple devices can communicate at the same time. These divided frequency bands are called channels.Wireless LAN devices must use the same

2022/09/23 12:53

Wireless LAN type

Wireless LAN type There are several standards for wireless LAN. Currently popular standards include IEEE802.11b, IEEE802.11g, IEEE802.11a, and IEEE802.11n. Depending on the standard, the radio frequency band to be used and the

2022/09/23 12:51

Wireless LAN (SSID, ESSID, ANY connection, stealth function)

Wireless LAN (SSID/ESSID) IEEE 802.11 series wireless LANs use identifiers called SSIDs to identify access points (wireless bridges, wireless broadband routers, etc.). This identifier can be any alphanumeric string up to 32 charac

2022/09/23 12:46

wireless network

What is a wireless networkWireless technology is now an integral part of building networks in both businesses and homes. After all, with wireless, you don't need to run a LAN cable to connect. You don't have to worry about the

2022/09/23 12:40

CSMA/CA

CSMA/CA CSMA/CA stands for "Carrier Sense Multiple Access with Collision Avoidance" and is also known as a carrier sense multiple access/collision avoidance scheme. It is adopted by the wireless LAN standards IEEE802.11a, IEEE802.

2022/09/23 12:38

PPPoE/PPPoA

What is PPPoEPPPoE (PPP over Ethernet) is a protocol for using PPP functions via Ethernet. PPP was originally developed for connecting to a network by dial-up or ISDN, and PPPoE enables PPP to be used in environments where ADSL and

2022/09/23 03:15

FTTH

What is FTTHFTTH is an abbreviation of Fiber To The Home, and refers to a network configuration that directly leads to general homes among FTTx. FTTx includes FTTH (Fiber To The Home), FTTC (Fiber To The Curb), and FTTB (Fiber To T

2022/09/23 03:12

ADSL

What is ADSL ADSL is an abbreviation for Asymmetric Digital Subscriber Line, and is a technology for high-speed data communication using general telephone lines (metallic cables). The frequency band used to carry phone voice is low

2022/09/23 03:06

PPP

What is PPP PPP is a data link layer protocol based on IOS DHLC and is the most familiar protocol used in WAN. It is used for dial-up, leased line, DSL, FTTH, etc., from abundant options such as authentication and compression.

2022/09/23 03:03

HDLC and Cisco HDLC

HDLC HDLC stands for High-Level Data Link Control. Also called high-level data link control procedures. It is a data link layer protocol standardized by ISO and is used in leased lines and circuit switching. Although poin

2022/09/23 02:58

Point-to-Point Connections and SLIP

point-to-point connectionSo far, we have explained the operation of TCP/IP with a focus on LANs. Then, what should be done to enable the TCP/IP mechanism that can be used in LAN to be used via public lines (telephone lines, etc.)?

2022/09/23 02:55

CSMA/CD

CSMA/CD CSMA/CD stands for "Carrier Sense Multiple Access with Collision Detection" and is a medium access control method used in Ethernet. It is also called a "first-come, first-served medium access control method" and is specifi

2022/09/23 02:50

Internet and Security Issues

Internet and security issues Web services that use HTTP require particular attention to security. Web services on the Internet have become the foundation of our lives. Electronic commerce, such as Internet shopping, auctions,

2022/09/23 02:48

WWW Service Mechanism

Mechanism of WWW service The WWW service operates on a client/server mechanism. On the WWW server side on the Internet, the http daemon is running and waiting. The browser on the client side enables browsing of homepages by c

2022/09/23 02:44

Port number that identifies the service

Port number that identifies the service Email software such as Outlook or Thunderburd has a field for you to enter the port number. Email software requires you to specify port numbers such as POP3 and SMTP. These numbers a

2022/09/23 02:41