《分享》網段169.254.XX.XX

IP從169.254.0.1到169.254.155.254的這個B級網段，我想網管人員一定都會有印象吧！
順子也是在接觸了部分網管工作後，才發現到這個奇怪的IP網段。

而究竟在什麼樣的情況下，會配發這個網段內的IP呢？
其實，只要DHCP伺服器無法正常配發虛擬IP給client端電腦時，就會由Windows自動配發這個網段的IP。

這是Automatic Private IP Addressing (APIPA)自動私人IP定址所提供的功能。
當TCP/IP通訊協定設定為自動取得位址，但無法使用Dynamic Host Configuration Protocol (DHCP)時，
便會自動設定從169.254.0.1到169.254.155.254之間的IP位址，及255.255.0.0的子網路遮罩。


以下為MSCE Training Kit的說明資料：

Using Automatic Private IP Addressing

The Windows 2000 implementation of TCP/IP supports a new mechanism for automatic address assignment of IP addresses for simple LAN-based network configurations. This addressing mechanism is an extension of dynamic IP address assignment for LAN adapters, enabling configuration of IP addresses without using static IP address assignment or installing the DHCP Service.

For the Automatic Private IP Addressing (APIPA) feature to function properly on a computer running Windows 2000, you must configure a network LAN adapter for TCP/IP and click Obtain An IP Address Automatically in the Internet Protocol (TCP/IP) Properties dialog box.


The following steps outline how APIPA assigns an IP address:

1. Windows 2000 TCP/IP attempts to find a DHCP server on the attached network to obtain a dynamically assigned IP address.
   
2. In the absence of a DHCP server during startup (for example, if the server is down for maintenance or repairs), the client cannot obtain an IP address.
   
3. APIPA generates an IP address in the form of 169.254.x.y (where x.y is the client's unique identifier) and a subnet mask of 255.255.0.0. If the address is in use, APIPA selects another IP address and, if necessary, reselects addresses up to 10 times.
   

♥順子老婆的網拍，請多關照∼

If you don't like something, change it.
If you can't change it, change your attitude.
Don't complain!