Solving network problems

- Introduction

Impact if no internet?

cannot play game

cannot validate software license

no social network

no youtube

no google

- Problem type

- Human

cable in the wrong hole?
router turn on?

- Hardware

network cable broken?
router setting?
firewall?
is network adapter working? driver installed? ip assigned?
isp problem?

how to setup a lan connector? Just refer the color of the old connector

- Broadband ISP hotline

- what checking is usually asked by the support?
ipconfig? cable? reboot router? reboot modem?

- Light of network card

The status LED's (right side facing) can show the following:
Off - The card is not receiving power or is in a boot up state
Solid Green - The card has valid IP settings
Solid Orange - The card has a fault
Flashing Green - The card does not have valid IP settings
Flashing Orange - The card is making BootP requests
Alternating Green/Orange
Rapidly - The card is booting up
Slowly - The card is making a DHCP request

The Link LED's (left side facing) can show the following
Off - The card is not receiving power, does not have a connected network cable or the device (switch/hub) connected to the card is not active
Solid Green - The card is on a network that communicates at 10mbps
Solid Orange - The card is on a network that communicates at 100mbps
Flashing Green - The card is receiving data packets at 10mbps
Flashing Orange - The card is receiving data packets at 100mbps

Category 5e

Though Cat5 and Cat5e cables are physically similar, Category 5e Ethernet adheres to more stringent IEEE standards.

“E” is for enhanced, meaning a lower-noise version where the potential for crosstalk is reduced. Crosstalk is interference that transfers from adjacent wires.

Cat5e is the most common type of cabling used for deployments due to its ability to support Gigabit speeds at a cost-effective price.

Even though both Cat5 and Cat5e support a maximum frequency of up to 100MHz, Cat5e has completely replaced its predecessor. Gigabit Ethernet utilizes 4 data pairs in comparison to Fast Ethernet which utilizes 2 data pairs.

Further, Cat 5e supports speeds of up to 1000 Mbps. It’s flexible enough for small space installations like residences, though it is still used in commercial spaces. Of all the current cabling options, Cat5e is your least expensive option.

NOTE: 100-250Mhz/1 Gbps/100m


http://www.cables-solutions.com/wp-content/uploads/2016/10/Cat-5e.jpg

- Category 6

Cat6 wiring can support up to 10 Gbps and frequencies of up to 250 MHz.

While Cat5e cable features 1.5-2 twists per cm, Cat6 cables are more tightly wound and feature 2 or more twists per cm. (The amount of twists per cm varies upon each cable manufacturer).

Cat6 cables also sport thicker sheaths in comparison to Cat5e.

Though standard Ethernet supports distances of up to 100 meters, CAT6 cable only supports 37-55 meters (depending on crosstalk) when transmitting 10 Gbps speeds.

Its thicker sheath protects against Near End Crosstalk (NEXT) and Alien Crosstalk (AXT).

Even though Cat6 and Cat6a cabling offer higher performance rates, many LANs still opt for CAT5e due to its cost-effectiveness and ability to support Gigabit speeds.

NOTE: 250-500Mhz/10 Gbps /100m.
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- Category 7

Cat7 can also support 10 Gbps

Laboratory testing has successfully shown its ability to transmit up to 40 Gb at 50 meters and even 100 Gb at 15 meters.

The newer “Class F” cabling can support frequencies of up to 600 Mhz. That said, Cat7 has not been approved as a cable standard for telecommunications.

Cat7 offers extensive shielding to reduce signal attenuation

Cat7 is relatively stiff in comparison to previous generations of cabling.

Both individual pairs are shielded, with an additional layer of shielding over the entire cable.

The shielding needs to be grounded and Cat7 also requires special GigaGate45 (GG45) connectors to take full advantage of higher performance features.

Cat6a can perform just about the same as Cat7 but at a lower price point.

Most of our AV and IP surveillance customers opt for Cat6a STP or Cat6a FTP. Both offer shielding from alien crosstalk and interference around high voltage lines.

Cat7 is suited for use in datacenters and large enterprise networks.

Note: 600Mhz/10Gbps/100m (40Gbps at 50m/100Gbps at 15m).

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- Windows command

ipconfig/renew

ping google.com -t

tracert google.com

what is default gateway?

what is ip 169.254.x.x?

DHCP - Dynamic Host Configuration Protocol 動態主機設定通訊協定

動態主機設定協定（DHCP）是一種使網路系統管理員能夠集中管理和自動分配IP網路位址的通信協議。在IP網路中，每個連接Internet的設備都需要分配唯一的IP位址。DHCP使網路系統管理員能從中心結點監控和分配IP地址。當某台電腦移到網路中的其它位置時，能自動收到新的IP位址。

DHCP使用了租約的概念，或稱為電腦IP位址的有效期。租用時間是不定的，主要取決於用戶在某地連接Internet需要多久，這對於教育行業和其它用戶頻繁改變的環境是很實用的。通過較短的租期，DHCP能夠在一個電腦比可用IP位址多的環境中動態地重新配置網路。DHCP支援為電腦分配靜態位址，如需要永久性IP位址的Web伺服器。

BOOTP是一種網路協定，讓電腦或其他周邊儀器可以從伺服器下載啟動程式。

BOOTP（Bootstrap Protocol）是DHCP的前身，本來是設計用來給無磁碟主機透過網路開機用的協定，它與DHCP最大的不同有：

1. 會要求一個boot file，用來開機。
2. 不支援動態 IP 分配，也因此BOOTP 客戶端不知道有關DHCP中租約時間的部份。

由於BOOTP與DHCP的封包格式極為相似，因此有的DHCP 伺服器也支援BOOTP協定， 也能夠回應BOOTP客戶端的請求，但是由於BOOTP不支援DHCP的租約時間選項， 因此DHCP伺服器在發放IP給BOOTP客戶端時，基本上是假設租約時間無上限，也就是不回收發給 BOOTP 客户端的IP地址。 

APIPA - Automatic Private IP Addressing 自動私人 IP 位址

APIPA是一個DHCP容錯移轉機制。當DHCP伺服器出故障時， APIPA在169.254.0.1到 169.254.255.254的私有空間內分配位址，所有設備使用預設的網路遮罩255.255.0.0。客戶機調整它們的位址使用它們在使用ARP的局域網中是唯一的。APIPA可以為沒有DHCP伺服器的單網段網路提供自動配置TCP/IP協定的功能。

Examples of Where APIPA May Be Useful

Example 1: No Previous IP Address and no DHCP Server

When your Windows-based computer (configured for DHCP) is initializing, it broadcasts three or more "discover" messages. If a DHCP server does not respond after several discover messages are broadcast, the Windows computer assigns itself a Class B (APIPA) address. Then the Windows computer will display an error message to the user of the computer (providing it has never been assigned an IP address from a DHCP server in the past). The Windows computer will then send out a Discover message every three minutes in an attempt to establish communications with a DHCP server.

Example 2: Previous IP Address and no DHCP Server

The computer checks for the DHCP server and if none are found, an attempt is made to contact the default gateway. If the default gateway replies, then the Windows computer retains the previously-leased IP address. However, if the computer does not receive a response from the default gateway or if none are assigned, then it uses the automatic private IP addressing feature to assign itself an IP address. An error message is presented to the user and discover messages are transmitted every 3 minutes. Once a DHCP server comes on line, a message is generated stating communications have been re-established with a DHCP Server.

Example 3: Lease Expires and no DHCP Server

The Windows-based computer tries to re-establish the lease of the IP address. If the Windows computer does not find a DCHP server, it assigns itself an IP address after generating an error message. The computer then broadcasts four discover messages, and after every 5 minutes it repeats the whole procedure until a DHCP server comes on line. A message is then generated stating that communications have been re-established with the DHCP Server.

範例 1：沒有先前的 IP 位址，也沒有 DHCP 伺服器

當您的 Windows 電腦 (已設定為適用於 DHCP) 正在初始化時，會廣播 3 項或更多的「探索」訊息。如果廣播數次探索訊息之後，DHCP 伺服器沒有回應，Windows 電腦就會自己指定「類別 B」(APIPA) 的位址。然後，Windows 電腦會向電腦的使用者顯示錯誤訊息 (如果電腦過去沒有從 DHCP 伺服器取得 IP 位址)。接著，Windows 電腦會每 3 分鐘傳送一次「探索」訊息，以試圖建立與 DHCP 伺服器的通訊。

範例 2：具有先前的 IP 位址，但沒有 DHCP 伺服器

電腦會查看 DHCP 伺服器，如果找不到 DHCP 伺服器，就會圖連接預設的閘道。如果預設閘道發出回覆，Windows 電腦就會保留先前租用的 IP 位址。然而，如果電腦沒有收到預設閘道的回應，或者沒有指定的預設閘道，就會使用自動私人 IP 位址自己指定 IP 位址。使用者會收到錯誤訊息，並且每 3 分鐘電腦就會傳送探索訊息。一旦 DHCP 伺服器連線，就會產生訊息，說明已經與 DHCP 伺服器重新建立通訊。

範例 3：租用到期且沒有 DHCP 伺服器

Windows 電腦試著重新建立 IP 位址的租用。如果 Windows 電腦沒有找到 DCHP 伺服器，就會在產生錯誤訊息之後，自己指定 IP 位址。然後電腦會廣播四個 Discover 訊息，之後每隔 5 分鐘便會重複整個程序，直到 DHCP 伺服器連線為止。接著會產生訊息，說明已經與 DHCP 伺服器重新建立通訊。