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1 应用环境
在OSPF中存在一个DR和BDR 其中DR=选择路由器 BDR=备份选择路由器
在广播和NBMA网络中,任何一台路由器的路由变化都能导致多次传递,浪费资源,为了解决这个问题,OSPF协议定义了选择DR和BDR
所有的路由器都发送LSA 但是只有DR和BDR和DR other 建立连接关系,所有路由器只将信息发送给DR, 由DR将LSA广播出去,BDR是DR的备份,再选取DR的同时也选取BDR, BDR也和本网段内所有的路由器建立邻接关系并且交换路由信息,当DR失效后,BDR将成为DR.除DR和BDR之外的路由器(称为DR Other)之间将不再建立邻接关系,也不再交换任何路由信息。这样就减少了广播网和NBMA网络上各路由器之间邻接关系的数量。
2 配置思路
在控制OSPF的DR选举时候,采用以下思路
1 配置路由器的router id, 启动ospf
2 配置优先级
3 查看相关的DR和BDR信息
3 配置注意事项
需要注意的是:
- 只有在广播或NBMA类型接口时才会选举DR,在点到点或点到多点类型的接口上不需要选举DR。
- DR是指某个网段的概念,是针对路由器的接口而言的。某台路由器在一个接口上可能是DR,在另一个接口上有可能是BDR,或者是DR Other。
- 若DR、BDR已经选择完毕,当一台新路由器加入后,即使它的DR优先级值最大,也不会立即成为该网段中的DR。
- DR并不一定就是DR优先级最大的路由器;同理,BDR也并不一定就是DR优先级第二大的路由器。
组网需求
在下图中,RouterA的GE1/0/0接口的优先级为100,它是网络上的最高优先级,所以RouterA被选为DR;RouterC的GE1/0/0接口的优先级仅次于RouterA的GE1/0/0接口,被选为BDR;RouterB的优先级为0,这意味着它将不参加DR选举;RouterD没有配置优先级,取缺省值1。
控制OSPF的DR选择组网图
适用的产品和版本
路由器端可以使用任意一款NE产品,版本为(VRP5.30)及后续版本。
配置步骤
步骤 1 配置各接口的IP地址(略)
步骤 2 配置OSPF基本功能
# 配置RouterA。
[RouterA] router id 1.1.1.1
[RouterA] ospf
[RouterA-ospf-1] area 0
[RouterA-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
# 配置RouterB。
[RouterB] router id 2.2.2.2
[RouterB] ospf
[RouterB-ospf-1] area 0
[RouterB-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
# 配置RouterC。
[RouterC] router id 3.3.3.3
[RouterC] ospf
[RouterC-ospf-1] area 0
[RouterC-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
# 配置RouterD。
[RouterD] router id 4.4.4.4
[RouterD] ospf
[RouterD-ospf-1] area 0
[RouterD-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
# 查看DR/BDR的状态。
[RouterA] display ospf peer
OSPF Process 1 with Router ID 1.1.1.1
Neighbors
Area 0.0.0.0 interface 192.168.1.1(GigabitEthernet1/0/0)'s neighbors
Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal
State: 2-Way Mode:Nbr is Master Priority: 1
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 32 sec
Neighbor is up for 00:04:21
Authentication Sequence: [ 0 ]
Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 37 sec
Neighbor is up for 00:04:06
Authentication Sequence: [ 0 ]
Router ID: 4.4.4.4 Address: 192.168.1.4 GR State: Normal
State: Full Mode:Nbr is Master Priority: 1
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 37 sec
Neighbor is up for 00:03:53
Authentication Sequence: [ 0 ]
查看RouterA的邻居信息,可以看到DR优先级(缺省为1)以及邻居状态,此时RouterD为DR,RouterC为BDR。
说明
当优先级相同时,router-id高的为DR。如果路由器的某个Ethernet接口成为DR之后,则这台路由器的其他广播接口在进行后续的DR选择时,具有高优先权。即选择已经是DR的路由器作为DR,DR不可抢占。
步骤 3 配置接口上的DR优先级
# 配置RouterA。
[RouterA] interface GigabitEthernet 1/0/0
[RouterA-GigabitEthernet1/0/0] ospf dr-priority 100
[RouterA-GigabitEthernet1/0/0] quit
# 配置RouterB。
[RouterB] interface GigabitEthernet 1/0/0
[RouterB-GigabitEthernet1/0/0] ospf dr-priority 0
[RouterB-GigabitEthernet1/0/0] quit
# 配置RouterC。
[RouterC] interface GigabitEthernet 1/0/0
[RouterC-GigabitEthernet1/0/0] ospf dr-priority 2
[RouterC-GigabitEthernet1/0/0] quit
# 查看DR/BDR的状态。
[RouterD] display ospf peer
OSPF Process 1 with Router ID 4.4.4.4
Neighbors
Area 0.0.0.0 interface 192.168.1.4(GigabitEthernet1/0/0)'s neighbors
Router ID: 1.1.1.1 Address: 192.168.1.1 GR State: Normal
State: Full Mode:Nbr is Slave Priority: 100
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 31 sec
Neighbor is up for 00:11:17
Authentication Sequence: [ 0 ]
Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal
State: Full Mode:Nbr is Slave Priority: 0
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 35 sec
Neighbor is up for 00:11:19
Authentication Sequence: [ 0 ]
Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal
State: Full Mode:Nbr is Slave Priority: 2
DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0
Dead timer due in 33 sec
Neighbor is up for 00:11:15
Authentication Sequence: [ 0 ]
说明
在接口上配置DR优先级之后并不会立即生效。
步骤 4 重启OSPF进程
在各路由器的用户视图下,同时执行命令reset ospf 1 process,以重启OSPF进程。
验证结果
# 查看OSPF邻居状态。
[RouterD] display ospf peer
OSPF Process 1 with Router ID 4.4.4.4
Neighbors
Area 0.0.0.0 interface 192.168.1.4(GigabitEthernet1/0/0)'s neighbors
Router ID: 1.1.1.1 Address: 192.168.1.1 GR State: Normal
State: Full Mode:Nbr is Slave Priority: 100
DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0
Dead timer due in 35 sec
Neighbor is up for 00:07:19
Authentication Sequence: [ 0 ]
Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal
State: 2-Way Mode:Nbr is Slave Priority: 0
DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0
Dead timer due in 35 sec
Neighbor is up for 00:07:19
Authentication Sequence: [ 0 ]
Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal
State: Full Mode:Nbr is Slave Priority: 2
DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0
Dead timer due in 37 sec
Neighbor is up for 00:07:17
Authentication Sequence: [ 0 ]
# 查看OSPF接口的状态。
[RouterA] display ospf interface
OSPF Process 1 with Router ID 1.1.1.1
Interfaces
Area: 0.0.0.0
IP Address Type State Cost Pri DR BDR
192.168.1.1 Broadcast DR 1 100 192.168.1.1 192.168.1.3
[RouterB] display ospf interface
OSPF Process 1 with Router ID 2.2.2.2
Interfaces
Area: 0.0.0.0
IP Address Type State Cost Pri DR BDR
192.168.1.2 Broadcast DROther 1 0 192.168.1.1 192.168.1.3
如果邻居的状态是Full,这说明它和邻居之间形成了邻接关系;如果停留在2-Way的状态,则说明他们都不是DR或BDR,两者之间不需要交换LSA。
如果OSPF接口的状态是DROther,则说明它既不是DR,也不是BDR。
配置文件
#
sysname RouterA
#
router id 1.1.1.1
#
interface GigabitEthernet1/0/0
ip address 192.168.1.1 255.255.255.0
ospf dr-priority 100
#
ospf 1
area 0.0.0.0
network 192.168.1.0 0.0.0.255
#
return
#
sysname RouterB
#
router id 2.2.2.2
#
interface GigabitEthernet1/0/0
ip address 192.168.1.2 255.255.255.0
ospf dr-priority 0
#
ospf 1
area 0.0.0.0
network 192.168.1.0 0.0.0.255
#
return
#
sysname RouterC
#
router id 3.3.3.3
#
interface GigabitEthernet1/0/0
ip address 192.168.1.3 255.255.255.0
ospf dr-priority 2
#
ospf 1
area 0.0.0.0
network 192.168.1.0 0.0.0.255
#
return
#
sysname RouterD
#
router id 4.4.4.4
#
interface GigabitEthernet1/0/0
ip address 192.168.1.4 255.255.255.0
#
ospf 1
area 0.0.0.0
network 192.168.1.0 0.0.0.255
#
return
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u/24661/showart_1169833.html |
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