OSPF（二）：接口狀態機（Interface Status Machine）

1、Down——初始化的接口狀態

2、Point-to-Point——僅適用於和點到點、點到多點以及虛電路等網絡相連的接口。在這個狀態下，接口將開始發送Hello報文，並嘗試和接口另一端的路由器建立鄰接關係

3、Waiting——僅適用於和廣播型、NBMA等網絡類型相連的接口。路由器在接口發送Hello報文並設置wait timer的同時試圖識別網絡上的DR和BDR

4、DR——在這種狀態下，路由器成爲所連網絡的DR，並將和多址網絡上的其他路由器建立鄰接關係

5、Backup——在這種狀態下，路由器成爲所連網絡的DR，並將和多址網絡上的其他路由器建立鄰接關係

6、DRother——僅僅會和網絡上的DR和BDR建立鄰接關係

7、Loopback

 

Input Event	Description
IE1	Lower-level protocols indicate that the network interface is operational.
IE2	Lower-level protocols indicate that the network interface is not operational.
IE3	Network management or lower-level protocols indicate that the interface is looped up.
IE4	Network management or lower-level protocols indicate that the interface is looped down.
IE5	A Hello packet is received in which either the originating neighbor lists itself as the BDR or the originating neighbor lists itself as the DR and indicates no BDR.
IE6	The wait timer has expired.
IE7	The router is elected as the DR for this network.
IE8	The router is elected as the BDR for this network.
IE9	The router has not been elected as the DR or BDR for this network.
IE10	A change has occurred in the set of valid neighbors on this network. This change may be one of the following: The establishment of two-way communication with a neighbor The loss of two-way communication with a neighbor The receipt of a Hello in which the originating neighbor newly lists itself as the DR or BDR The receipt of a Hello from the DR in which that router is no longer listed as the DR The receipt of a Hello from the BDR in which that router is no longer listed as the BDR The expiration of the RouterDeadInterval without having received a Hello from the DR or the BDR or both