前文我們了解了OSPF建立鄰居關系的條件，回顧請參考https://www.cnblogs.com/qiuhom-1874/p/15032907.html；今天我們來聊一聊OSPF中的DR和BDR；
在說DR和BDR之前我們先來了解下OSPF的網絡類型；
首先OSPF的網絡類型是基于接口來劃分，其次OSPF的網絡類型是通過接口的二層封裝封包的方式進行了劃分，預設情況下OSPF把接口二層是以太網封裝的網絡稱為廣播類型，把接口二層是PPP或者HDLC封裝的網絡稱為點到點類型；
在生活中，廣播就是一個人說話，在同一個房間裡的其他人都可以聽到；在網絡裡，廣播和這個類似；一個網絡裝置在一個廣播域發送一條廣播封包，在同一個廣播域的所有裝置都能收到該裝置的廣播；這樣一來我們要想和其中的一台裝置通訊怎麼通訊呢？在二層為以太網封裝的廣播類型網絡裡，它是通過二層以太網封裝目标MAC和源MAC；其原因是ip位址是變化的，如果單純的使用ip位址不能夠準确的辨別某一台裝置（因為ip位址是變化的），而MAC位址是裝置的硬體位址，這個位址是裝置出廠時就固定了，況且不會發生變化；是以确定一台裝置的唯一性，我們可以通過MAC位址；有了通信雙方的mac位址再結合三層的ip位址，我們就可以準确的将對應資料包發送給對方；
對于點到點類型的網絡，其二層就不需要封裝MAC位址，一條鍊路上就隻有兩個端點，在A端點發送資料B端點就一定能收到；
提示：廣播類型的接口是以太網類型接口（就是我們常常看到的網口），而點到點類型的接口是序列槽；
在點對點類型的網絡中，基于接口封裝的不同又可以分非廣播多路通路和點到多點，如下圖
提示：預設情況下，OSPF認為幀中繼（FR）、異步傳輸（ATM）的網絡類型為NBMA；在幀中繼網絡裡非廣播多路通路和以太網中的廣播類型，兩者有一個相同的特點，就是都可以接多個裝置；不同點是以太網二層封裝需要封裝mac位址，支援廣播發送，而幀中繼網絡二層不需要封裝mac位址，其原因是它不支援廣播；不支援廣播就意味着在ospf裡不支援多點傳播；不支援多點傳播也就是說幀中繼網絡裡，ospf隻能通過單點傳播的方式建立鄰居；
實驗：如下圖兩個拓撲，R1和R2為以太網類型接口，R3和R4為序列槽接口，在兩個實驗環境中配置ospf，抓包看看兩者發送到hello包有什麼不同
sys
sys R1
int g0/0/0
ip add 12.0.0.1 24
ospf 1 router-id 1.1.1.1
area 0
net 12.0.0.1 0.0.0.0
dis ip int b View Code
配置R2
sys
sys R2
int g0/0/0
ip add 12.0.0.2 24
ospf 1 router-id 2.2.2.2
area 0
net 12.0.0.2 0.0.0.0
dis ip int b 配置R3
sys
sys R3
int s4/0/0
ip add 34.0.0.3 24
ospf 1 router-id 3.3.3.3
area 0
net 34.0.0.3 0.0.0.0
dis ip int b 配置R4
sys
sys R4
int s4/0/0
ip add 34.0.0.4 24
ospf 1 router-id 4.4.4.4
area 0
net 34.0.0.4 0.0.0.0
dis ip int b 在R1或R2上抓包
在R3或R4上抓包
提示：預設情況序列槽鍊路的二層封裝為ppp類型，這裡抓包就選擇ppp鍊路類型即可；
提示：從上面的抓包情況可以看到，在以太網封類型的網絡環境下抓包，其二層封裝了目标mac和源mac，而在點到點類型的網絡環境下抓包，其二層就不是使用以太網協定而是用ppp協定，并且資料包裡面也沒有封裝mac位址；
驗證：檢視對應ospf網絡類型
在R1或R2上驗證相關接口的網絡類型
在R3或R4上驗證相關接口的網絡類型
更改R3的s4/0/0的鍊路封裝為FR，看看對應的接口類型是什麼
提示：可以看到修改了R3的s4/0/0接口的封裝為FR以後，對應ospf就down掉了；并且對應接口的類型就變為了NBMA（非廣播多路通路）；
OSPF DR和BDR
DR和BDR的作用
在上述的網絡類型中，在多路通路網絡類型中跑OSPF，每個路由器都會和其他路由器建立鄰居，一個路由器發送一條鍊路更新，其他路由器都會跟着确認，這樣一來，每個路由器都要經過兩兩的互動和确認，在一定程度上會帶來路由器的性能的開銷（hello包，DD，LSR，LSU，LSACK這些包過多，增加路由器的處理壓力，進而導緻路由器的性能降低）；為了降低資料包的交換，在OSPF中會選舉DR和BDR；如下圖
提示：廣播型網絡BMA和NBMA網絡中，為了減少鄰接關系的數量，進而減少資料包交換，次數，最終節省帶寬，降低對路由器處理能力的壓力，選舉DR和BDR。
相關術語概述
DR：Designed Router，指定路由器，類似班長、總經理；
BDR：Backup DR，備用DR，類似副班長、副總經理；
DRouthers：類似普通學生、普通員工；
三者的關系：DR、BDR、DRothers之間都保持鄰接關系（Full），DRothers之間保持鄰居關系（Two-Way）；
通信位址：224.0.0.6向DR和BDR發送鍊路狀态更新，224.0.0.5向所有OSPF路由器發送；
DR選舉規則
1、首先比較Hello封包中攜帶的優先級，優先級範圍是0-255，預設情況下都是1；優先級最高的被選舉為DR，優先級次高的被選舉為BDR；優先級為0的不參與選舉；
2、如果優先級相同的情況下，比較router id大小，router id越大越優先；
3、選舉不具有搶占性，除非當DR和BDR都失效或重新開機OSPF程序；
提示：DRothers的LSU向DR或BDR通過224.0.0.6發送，然後DR收到DRothers發送到LSU以後，會将對應的LSU通過224.0.0.5向其他路由器發送，其他路由器收到DR發送LSU以後，BDR向224.0.0.5直接确認，而DBothers則通過224.0.0.6向DR确認；總結一句話就是從DR或BDR發出的資料包都是發往224.0.0.5，DR和BDR都會監聽224.0.0.6這個位址；DRothers發出的資料會通過224.0.0.6向DR或BDR發送；
實驗：如下圖，全網運作ospf，看看對應的資料包會這麼發送，對應路由器之間是什麼關系
sys
sys R1
int g0/0/0
ip add 1.0.0.1 24
ospf 1 router-id 1.1.1.1
a 0
net 1.0.0.0 0.0.0.255
dis ip int b
dis ospf peer brief 在R1上檢視g0/0/0的接口資訊，看看誰是DR和BDR
提示：可以看到隻配置了R1上的OSPF以後，對應DR就是它自己，因為此時沒有其他裝置和它競選DR，是以隻有它是DR；對于BDR來說，它不知道，因為目前就隻有它自己在ospf裡面，沒有看到其他裝置；
sys
sys R2
int g0/0/0
ip add 1.0.0.2 24
ospf 1 router-id 2.2.2.2
a 0
net 1.0.0.0 0.0.0.255
dis ip int b
dis ospf peer brief <Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sys R2
[R2]int g0/0/0
[R2-GigabitEthernet0/0/0]ip add 1.0.0.2 24
[R2-GigabitEthernet0/0/0]ospf 1 rout
Jul 24 2021 12:08:39-08:00 R2 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP on the interface GigabitEthernet0/0/0 has entered the UP state.
[R2-GigabitEthernet0/0/0]ospf 1 router-id 2.2.2.2
[R2-ospf-1]a 0
[R2-ospf-1-area-0.0.0.0]net 1.0.0.0 0.0.0.255
[R2-ospf-1-area-0.0.0.0]dis ip int b
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 2
The number of interface that is DOWN in Physical is 2
The number of interface that is UP in Protocol is 2
The number of interface that is DOWN in Protocol is 2
Interface IP Address/Mask Physical Protocol
GigabitEthernet0/0/0 1.0.0.2/24 up up
GigabitEthernet0/0/1 unassigned down down
GigabitEthernet0/0/2 unassigned down down
NULL0 unassigned up up(s)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[1]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[2]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[3]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=ExStart)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[4]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=NegotiationDone, NeighborPreviousState=ExStart, NeighborCurrentState=Exchange)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[5]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=ExchangeDone, NeighborPreviousState=Exchange, NeighborCurrentState=Loading)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:08:44-08:00 R2 %%01OSPF/4/NBR_CHANGE_E(l)[6]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=LoadingDone, NeighborPreviousState=Loading, NeighborCurrentState=Full)
[R2-ospf-1-area-0.0.0.0]dis ospf peer brief
OSPF Process 1 with Router ID 2.2.2.2
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.0 GigabitEthernet0/0/0 1.1.1.1 Full
----------------------------------------------------------------------------
[R2-ospf-1-area-0.0.0.0]
提示：可以看到當R2配置好ospf以後，它會和R1先建立其鄰接關系；
再次在R1上檢視g0/0/0的接口資訊，看看此時誰是DR和BDR
提示：此時可以看到DR是R1的接口ip位址，BDR是R2的接口位址；
sys
sys R3
int g0/0/0
ip add 1.0.0.3 24
ospf 1 router-id 3.3.3.3
a 0
net 1.0.0.0 0.0.0.255
dis ip int b
dis ospf peer brief <Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sys R3
[R3]int g0/0/0
[R3-GigabitEthernet0/0/0]ip add 1.0.0.3 24
Jul 24 2021 12:14:41-08:00 R3 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP on the interface GigabitEthernet0/0/0 has entered the UP state.
[R3-GigabitEthernet0/0/0]ospf 1 router-id 3.3.3.3
[R3-ospf-1]a 0
[R3-ospf-1-area-0.0.0.0]net 1.0.0.0 0.0.0.255
[R3-ospf-1-area-0.0.0.0]dis ip int b
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 2
The number of interface that is DOWN in Physical is 2
The number of interface that is UP in Protocol is 2
The number of interface that is DOWN in Protocol is 2
Interface IP Address/Mask Physical Protocol
GigabitEthernet0/0/0 1.0.0.3/24 up up
GigabitEthernet0/0/1 unassigned down down
GigabitEthernet0/0/2 unassigned down down
NULL0 unassigned up up(s)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:45-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[1]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:45-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[2]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[3]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[4]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[5]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=ExStart)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[6]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=ExStart)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[7]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=NegotiationDone, NeighborPreviousState=ExStart, NeighborCurrentState=Exchange)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[8]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=NegotiationDone, NeighborPreviousState=ExStart, NeighborCurrentState=Exchange)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[9]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=ExchangeDone, NeighborPreviousState=Exchange, NeighborCurrentState=Loading)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[10]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=LoadingDone, NeighborPreviousState=Loading, NeighborCurrentState=Full)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[11]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=ExchangeDone, NeighborPreviousState=Exchange, NeighborCurrentState=Loading)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:14:46-08:00 R3 %%01OSPF/4/NBR_CHANGE_E(l)[12]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=LoadingDone, NeighborPreviousState=Loading, NeighborCurrentState=Full)
[R3-ospf-1-area-0.0.0.0]dis ospf peer brief
OSPF Process 1 with Router ID 3.3.3.3
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.0 GigabitEthernet0/0/0 1.1.1.1 Full
0.0.0.0 GigabitEthernet0/0/0 2.2.2.2 Full
----------------------------------------------------------------------------
[R3-ospf-1-area-0.0.0.0]
提示：可以看到當R3配置好以後，對應R3和R1和R2都建立起鄰接關系；
檢視R3g0/0/0接口資訊，看看DR和BDR變化沒有？
提示：之是以DR和BDR沒有發生變化，其原因是ospf已經選好了DR和BDR，而DR和BDR的選舉是非搶占性，一旦選好，就不變了，除非重新開機ospf程序（所有路由器）來觸發DR和BDR的重新選舉；
sys
sys R4
int g0/0/0
ip add 1.0.0.4 24
ospf 1 router-id 4.4.4.4
a 0
net 1.0.0.0 0.0.0.255
dis ip int b
dis ospf peer brief <Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sys R4
[R4]int g0/0/0
[R4-GigabitEthernet0/0/0]ip add 1.0.0.4 24
Jul 24 2021 12:20:57-08:00 R4 %%01IFNET/4/LINK_STATE(l)[0]:The line protocol IP on the interface GigabitEthernet0/0/0 has entered the UP state.
[R4-GigabitEthernet0/0/0]ospf 1 router-id 4.4.4.4
[R4-ospf-1]a 0
[R4-ospf-1-area-0.0.0.0]net 1.0.0.0 0.0.0.255
[R4-ospf-1-area-0.0.0.0]dis ip int b
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 2
The number of interface that is DOWN in Physical is 2
The number of interface that is UP in Protocol is 2
The number of interface that is DOWN in Protocol is 2
Interface IP Address/Mask Physical Protocol
GigabitEthernet0/0/0 1.0.0.4/24 up up
GigabitEthernet0/0/1 unassigned down down
GigabitEthernet0/0/2 unassigned down down
NULL0 unassigned up up(s)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[1]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[2]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[3]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=ExStart)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[4]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=NegotiationDone, NeighborPreviousState=ExStart, NeighborCurrentState=Exchange)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[5]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=ExchangeDone, NeighborPreviousState=Exchange, NeighborCurrentState=Loading)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:02-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[6]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=2.0.0.1, NeighborEvent=LoadingDone, NeighborPreviousState=Loading, NeighborCurrentState=Full)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:04-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[7]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:04-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[8]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:04-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[9]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=ExStart)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:05-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[10]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=NegotiationDone, NeighborPreviousState=ExStart, NeighborCurrentState=Exchange)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:05-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[11]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=ExchangeDone, NeighborPreviousState=Exchange, NeighborCurrentState=Loading)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:05-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[12]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=1.0.0.1, NeighborEvent=LoadingDone, NeighborPreviousState=Loading, NeighborCurrentState=Full)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:06-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[13]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=3.0.0.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down, NeighborCurrentState=Init)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:06-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[14]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=3.0.0.1, NeighborEvent=2WayReceived, NeighborPreviousState=Init, NeighborCurrentState=2Way)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
Jul 24 2021 12:21:06-08:00 R4 %%01OSPF/4/NBR_CHANGE_E(l)[15]:Neighbor changes event: neighbor status changed. (ProcessId=256, NeighborAddress=3.0.0.1, NeighborEvent=AdjOk?, NeighborPreviousState=2Way, NeighborCurrentState=2Way)
[R4-ospf-1-area-0.0.0.0]dis ospf peer brief
OSPF Process 1 with Router ID 4.4.4.4
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.0 GigabitEthernet0/0/0 1.1.1.1 Full
0.0.0.0 GigabitEthernet0/0/0 2.2.2.2 Full
0.0.0.0 GigabitEthernet0/0/0 3.3.3.3 2-Way
----------------------------------------------------------------------------
[R4-ospf-1-area-0.0.0.0]
提示：可以看到當R4配置好以後，對應R4和R1（DR），R2（BDR）是鄰接關系；而和R3（DRothers）建立的鄰居關系；
驗證：在R1上釋出更新，抓包看看對應的資料包會怎麼發送和确認？
提示：可以看到當R1（DR）發送LSU時，它會直接向224.0.0.5發送；其中R2（BDR）向224.0.0.5确認；R3（DRothers）和R4（DRothers）向224.0.0.6确認；
驗證：在R2上發送LSU，看看對應資料包會這麼發送和确認的呢？
提示：可以看到當R2（BDR）發送LSU時，它和R1發送LSU一樣直接向224.0.0.5發送LSU，對應R1（DR）直接向224.0.0.5确認；R3、R4（DRother）向224.0.0.6确認；
驗證：當R3發送LSU，看看對應資料包會這麼發送和确認呢？
提示：可以看到當R3（DRother）發送LSU時，它首先會把LSU通過224.0.0.6向R1（DR）發送，當R1（DR）收到R3發送的LSU，它會通過224.0.0.5向其他路由器發送LSU（不會再發送給R3）；R2（BDR）收到LSU向224.0.0.5确認，R4（DRother）向224.0.0.6确認；
驗證：當R4 發送LSU時，看看對應資料包會怎麼發送和确認呢？
提示：可以看到R4（DRother）發送LSU和R3（DRother）發送LSU一樣；首先它會把LSU發送給R1（DR），然後由R1（DR）再向其他路由器發送LSU；BDR（R2）直接向224.0.0.5确認；DRother（R3）向224.0.0.6确認；
驗證：全網重新開機ospf程序，看看對應的DR和BDR是否會重新選舉？
提示：可以看到4個路由器分别重新啟動了ospf以後，重置ospf 程序以後，R4當選為DR，R3當選為BDR；因為重新開機ospf程序對應的鄰居和鄰接關系又重建立立，此時4個路由器首先會比較對應的hello包裡的優先級，預設情況下優先級都是1 ，此時優先級一樣，會比較對應接口的ip位址誰大誰就是DR，次大者就為BDR，剩下沒有被選舉成DR或BDR的就淪為DRother；R4的router id 為4.4.4.4，是4個路由器中最大的，是以R4當選DR，R3的router id為3.3.3.3 ，第二大，是以當選BDR；
作者：Linux-1874
出處：https://www.cnblogs.com/qiuhom-1874/
本文版權歸作者和部落格園共有，歡迎轉載，但未經作者同意必須保留此段聲明，且在文章頁面明顯位置給出原文連接配接，否則保留追究法律責任的權利.