实验室之OSPF篇：帧中继承载OSPF – 非广播（Non-Broadcast）

帧中继承载OSPF – 非广播（Non-Broadcast）

目标：

在R1，R4和R5之间的帧中继网络中配置OSPF，网络类型为non-broadcast，实现VLAN A, VLAN B和VLAN C的互通

配置指南：

• 在R1上配置接口Ethernet0/0地址为1.0.0.1/8

• 在R4上配置接口Ethernet0/0地址为4.0.0.4/8

• 在R5上配置接口Ethernet0/0地址为5.0.0.5/8

• 在R1上配置接口Seria0/0地址为10.0.0.1/8

• 在R4上配置接口Serial0/0地址为10.0.0.4/8

• 在R5上配置接口Serial0/0地址为10.0.0.5/8

• 在R1,R4和R5的Serial接口上配置帧中继封装(Frame Relay encapsulation)

• 在R4和R5上禁用帧中继反向地址解析(Frame-Relay Inverse-ARP)

• 在R1上配置静态映射，通过DCLI104到10.0.0.4和通过DLCI105到10.0.0.5

• 在R4上配置静态映射，通过DLCI401到10.0.0.1和10.0.0.5

• 在R5上配置静态映射，通过DLCI501到10.0.0.1 和10.0.0.4

• 在R4和R5配置Serial接口OSPF优先级为0

• 配置R1, R4和R5中所有接口加入area 0

• 在R1上配置对R4 和R5的邻居命令

自我提问：

• 在多点的帧中继接口(multipoint Frame Relay interface)上缺省的OSPF网络类型是什么？

• 这种网络类型中LSA是单播还是组播发送?

• 这种网络类型支持DR/BDR 选举吗?

• 这些属性对配置有什么影响?

最终配置和验证：

R1:

interface Ethernet0/0

ip address 1.0.0.1 255.0.0.0

!

interface Serial0/0

ip address 10.0.0.1 255.0.0.0

encapsulation frame-relay

frame-relay map ip 10.0.0.4 104

frame-relay map ip 10.0.0.5 105

!

router ospf 1

network 0.0.0.0 255.255.255.255 area 0

neighbor 10.0.0.4

neighbor 10.0.0.5

 

R4:

interface Ethernet0/0

ip address 4.0.0.4 255.0.0.0

!

interface Serial0/0

ip address 10.0.0.4 255.0.0.0

encapsulation frame-relay

ip ospf priority 0

frame-relay map ip 10.0.0.1 401

frame-relay map ip 10.0.0.5 401

no frame-relay inverse-arp

!

router ospf 1

network 0.0.0.0 255.255.255.255 area 0

 

R5:

interface Ethernet0/0

ip address 5.0.0.5 255.0.0.0

!

interface Serial0/0

ip address 10.0.0.5 255.0.0.0

encapsulation frame-relay

ip ospf priority 0

frame-relay map ip 10.0.0.1 501

frame-relay map ip 10.0.0.4 501

no frame-relay inverse-arp

!

router ospf 1

network 0.0.0.0 255.255.255.255 area 0

 

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.0.0.4 0 FULL/DROTHER 00:01:58 10.0.0.4 serial0/0

10.0.0.5 0 FULL/DROTHER 00:01:49 10.0.0.5 serial0/0

R4#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.0.0.1 1 FULL/DR 00:01:47 10.0.0.1 serial0/0

R5#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.0.0.1 1 FULL/DR 00:01:56 10.0.0.1 serial0/0

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C 1.0.0.0/8 is directly connected, Ethernet0/0

O 4.0.0.0/8 [110/74] via 10.0.0.4, 00:01:49, Serial0/0

O 5.0.0.0/8 [110/74] via 10.0.0.5, 00:01:49, Serial0/0

C 10.0.0.0/8 is directly connected, Serial0/0

R4#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

O 1.0.0.0/8 [110/74] via 10.0.0.1, 00:02:26, Serial0/0

C 4.0.0.0/8 is directly connected, Ethernet0/0

O 5.0.0.0/8 [110/74] via 10.0.0.5, 00:02:26, Serial0/0

C 10.0.0.0/8 is directly connected, Serial0/0

R5#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

O 1.0.0.0/8 [110/74] via 10.0.0.1, 00:00:11, Serial0/0

O 4.0.0.0/8 [110/74] via 10.0.0.4, 00:00:11, Serial0/0

C 5.0.0.0/8 is directly connected, Ethernet0/0

C 10.0.0.0/8 is directly connected, Serial0/0

 

注解：

对于多点的帧中继接口缺省的网络类型是nonbroadcast，这种网络类型使用单播来传递OSPF hello包，像广播网络一样支持DR/BDR选举。由于hello数据包是单播，所以必须在DR和BDR上手动配置邻居。注意的是在例子的frame-relay map命令中没有使用broadcast选项，因为是单播不是组播包。

前面例子中提到了OSPF不支持抢占和对于hub-spoke网络的特殊要求，所以本例中在R4和R5这两个spoke路由器上配置优先级为0。

通过使用show ip ospf neighbor命令来验证邻居关系，使用show ip ospf interface命令来验证网络类型和DR/BDR。

还有一个有趣的现象就是在show ip route输出中的next-hop 值。比如R4的路由表可以看到到达网络5.0.0.0的下一跳为10.0.0.5，而物理上R4还是先要把数据包发送给R1。这也就是说R4必须有一个针对10.0.0.5地址的三层到二层的解析，同理针对Rr5必须有一个针对10.0.0.4的解析。