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帧中继多点子接口下配置OSPF
1、实验目的
通过本实验可以掌握
A、帧中继多点子接口的特征
B、帧中继多点子接口的配置
C、NBMA模式下OSPF的配置和调试
D、手工配置OSPF邻居
E、NBMA模式下的DR选举
2、实验拓扑
3、实验步骤
本实验分别在路由器R1、R3和R4尚创建多点子接口，拓扑结构采用Hub-and-Spoke结构，整个网络运行OSPF路由协议。
A.配置路由器R1
R1(config)#int loopback0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#ip ospf networkpoint-to-point //修改OSPF网络类型
R1(config-if)#exit
R1(config)#int s1/0
R1(config-if)#no ip address //物理接口下不要配置IP地址
R1(config-if)#encapsulation frame-relay //接口封装帧中继
R1(config-if)#no frame-relay inverse-arp //关闭帧中继逆向ARP解析
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#int serial 1/0.1 multipoint //创建帧中继多点子接口
【技术要点】
“int serial slot-number/interface-number.subinterface-number{ multipoint|point-to-point }”命令用来创建帧中继子接口，其中：
1）slot-number/interface-number：物理接口的号；
2）subinterface-number：是自接口号，范围为1~4 294 967 293；
3）multipoint |point-to-point：属于必须选择的项，是子接口的类型，要么是多点类型，要么是点到点类型。
R1(config-subif)#ip address 192.168.134.1 255.255.255.0
R1(config-subif)#frame-relay map ip 192.168.134.3 103broadcast
R1(config-subif)#frame-relay map ip 192.168.134.4 104broadcast
R1(config-subif)#frame-relay map ip 192.168.134.1 103
R1(config-subif)#no frame-relay inverse-arp
R1(config-subif)#exit
R1(config)#router ospf 1
R1(config-router)#router-id 1.1.1.1
R1(config-router)#network 192.168.1.0 0.0.0.255 area 0
R1(config-router)#network 192.168.134.0 0.0.0.255 area 0
R1(config-router)#neighbor 192.168.134.3 //手工指定OSPF邻居
R1(config-router)#neighbor 192.168.134.4
B.配置路由器R3：
R3#conf t
Enterconfiguration commands, one per line. End with CNTL/Z.
R3(config)#intlo0
R3(config-if)#ipaddress 192.168.3.1 255.255.255.0
R3(config-if)#noshutdown
R3(config-if)#ipospf network point-to-point
R3(config-if)#exit
R3(config)#ints1/1
R3(config-if)#noip address
R3(config-if)#encapsulationframe-relay
R3(config-if)#noframe-relay inverse-arp
R3(config-if)#noshutdown
R3(config-if)#exit
R3(config)#ints1/1.1 multipoint
R3(config-subif)#ipaddress 192.168.134.3 255.255.255.0
R3(config-subif)#ipospf priority 0
//配置spoke端OSPF接口优先级为0，确保HUB端路由器R1成为DR
R3(config-subif)#frame-relaymap ip 192.168.134.1 301 broadcast
R3(config-subif)#frame-relaymap ip 192.168.134.4 301 broadcast
R3(config-subif)#frame-relaymap ip 192.168.134.3 301
R3(config-subif)#noframe-relay inverse-arp
R3(config-subif)#exit
R3(config)#routerospf 1
R3(config-router)#router-id3.3.3.3
R3(config-router)#network192.168.134.0 0.0.0.255 area 0
R3(config-router)#network192.168.3.0 0.0.0.255 area 0
【提示】
可以使用“no interfaceSerial1/1.1”命令来删除子接口。然而需要重新启动路由器，该子接口才真正被删除。
C.配置路由器R4：
R4#conf t
Enterconfiguration commands, one per line. End with CNTL/Z.
R4(config)#intlo0
R4(config-if)#ipaddress 192.168.4.1 255.255.255.0
R4(config-if)#ipospf network point-to-point
R4(config-if)#noshutdown
R4(config-if)#exit
R4(config)#ints1/2
R4(config-if)#noip address
R4(config-if)#encapsulationframe-relay
R4(config-if)#noframe-relay inverse-arp
R4(config-if)#noshutdown
R4(config-if)#exit
R4(config)#ints1/2.1 multipoint
R4(config-subif)#ipaddress 192.168.134.4 255.255.255.0
R4(config-subif)#ipospf priority 0
R4(config-subif)#frame-relaymap ip 192.168.134.1 401 broadcast
R4(config-subif)#frame-relaymap ip 192.168.134.3 401 broadcast
R4(config-subif)#frame-relaymap ip 192.168.134.4 401
R4(config-subif)#noframe-relay inverse-arp
R4(config-subif)#exit
R4(config)#routerospf 1
R4(config-router)#router-id4.4.4.4
R4(config-router)#network192.168.134.0 0.0.0.255 area 0
R4(config-router)#network192.168.4.0 0.0.0.255 area 0
D．帧中继交换机配置：
R2#conf t
Enterconfiguration commands, one per line. End with CNTL/Z.
R2(config)#frame-relayswitching
R2(config)#ints1/0
R2(config-if)#clockrate 64000
R2(config-if)#encapsulationframe-relay
R2(config-if)#nosh
R2(config-if)#frame-relaylmi-type cisco
R2(config-if)#frame-relayintf-type dce
R2(config-if)#frame-relayroute 103 interface s1/1 301
R2(config-if)#frame-relayroute 104 interface s1/2 401
R2(config-if)#exit
R2(config)#ints1/1
R2(config-if)#clockrate 64000
R2(config-if)#encapsulationframe-relay
R2(config-if)#noshutdown
R2(config-if)#frame-relaylmi-type cisco
R2(config-if)#frame-relayintf-type dce
R2(config-if)#frame-relayroute 301 interface s1/0 103
R2(config-if)#exit
R2(config)#ints1/2
R2(config-if)#clockrate 64000
R2(config-if)#encapsulationframe-relay
R2(config-if)#frame-relaylmi-type cisco
R2(config-if)#frame-relayintf-type dce
R2(config-if)#frame-relayroute 401 interface s1/0 104
R2(config-if)#
【技术要点】
1）在帧中继网络上，OSPF接口默认的网络类型为NON_BROADCAST。在这种模式下，OSPF不会在帧中继接口上发送Hello包，因此无法建立最基本的OSPF邻接关系。可以手工使用“neighbor”命令来指定邻居，这时Hello包以单播形式发送。
2）NBMA属于多路访问网络，所以要进行DR选举，由于Hello包只能传1跳，所以在Hub-and-Spoke结构中，必须控制处于“HUB”端的路由器成为DR，最保险的办法就是将“Spoke”端路由器OSPF接口优先级配置为0，使之不参与DR选举，“HUB”端的路由器自然就成为DR；否则，可能会导致路由学习不正常。
3）在接口模式下，可以通过如下命令修改OSPF的网络类型：
R3(config-if)#ip ospf network { broadcast | point-to-point| non_broadcast | point-to-multipoint }
4）多点子接口不能解决接口水平分割的问题，只是节省了物理接口而已。
4、实验调试
1）show frame-relay map
R1#showframe-relay map
Serial1/0.1(up): ip 192.168.134.1 dlci 103(0x67,0x1870), static,
CISCO, status defined, active
Serial1/0.1(up): ip 192.168.134.3 dlci 103(0x67,0x1870), static,
broadcast,
CISCO, status defined, active
Serial1/0.1(up): ip 192.168.134.4 dlci 104(0x68,0x1880), static,
broadcast,
CISCO, status defined, active
R1#
以上输出表明路由器R1使用多点子接口S1/0.1，该子接口下有3条帧中继静态映射。
2）show ip ospf interface
R1#showip ospf interface
Serial1/0.1is up, line protocol is up
Internet Address 192.168.134.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network TypeNON_BROADCAST, Cost: 64
//接口网络类型为NBMA模式
Transmit Delay is 1 sec, State DR, Priority 1
//状态为DR，接口优先级为1
Designated Router (ID) 1.1.1.1, Interfaceaddress 192.168.134.1
//DR的ID和接口地址
No backup designated router on this network
//没有BDR
Timer intervals configured, Hello 30, Dead120, Wait 120, Retransmit 5
//NBMA模式下，Hello间隔为30S，Dead保持时间为120S
oob-resync timeout 120
Hello due in 00:00:10
Supports Link-local Signaling (LLS)
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 4msec
Neighbor Count is 2, Adjacent neighbor countis 2
//有2个OSPF邻居，都形成了邻接关系
Adjacent with neighbor 3.3.3.3
Adjacent with neighbor 4.4.4.4
//以上两行表明路由器R1与路由器R3和R4形成邻接关系
Suppress hello for 0 neighbor(s)
3）show ip route
R1#showip route ospf
O 192.168.4.0/24 [110/65] via 192.168.134.4,00:40:37, Serial1/0.1
O 192.168.3.0/24 [110/65] via 192.168.134.3,00:40:37, Serial1/0.1
R1#
R3#showip route ospf
O 192.168.4.0/24 [110/65] via 192.168.134.4,00:41:32, Serial1/1.1
O 192.168.1.0/24 [110/65] via 192.168.134.1,00:41:32, Serial1/1.1
R3#
R4#showip route ospf
O 192.168.1.0/24 [110/65] via 192.168.134.1,00:42:10, Serial1/2.1
O 192.168.3.0/24 [110/65] via 192.168.134.3,00:42:10, Serial1/2.1
R4#
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