用模拟器配的，拓扑图很简单，不好上传，描述一下吧！用了4个3640三层交换
机，R1，R2，R3，R4，其中R2模拟帧中继交换机。具体的拓扑连接是这样的：
R2的S0/0连R1的S0/1，R2的S0/1连R3的S0/1，R2的S0/2连R4的S0/1。具体的配
置是这样的：
R1:
interface Loopback0
 ip address 1.1.1.1 255.255.255.0
interface Serial0/1
 ip address 192.168.1.1 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint non-broadcast
 serial restart-delay 0
 frame-relay map ip 192.168.1.3 103
 frame-relay map ip 192.168.1.4 104
 no frame-relay inverse-arp
router ospf 1
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area
FR:
frame-relay switching
interface Serial0/0
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clockrate 64000
 frame-relay intf-type dce
 frame-relay route 103 interface Serial0/1 301
 frame-relay route 104 interface Serial0/2 401
!
interface Serial0/1
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clockrate 64000
 frame-relay intf-type dce
 frame-relay route 301 interface Serial0/0 103
!
interface Serial0/2
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clockrate 64000
 frame-relay intf-type dce
 frame-relay route 401 interface Serial0/0 104
R3:
interface Loopback0
 ip address 3.3.3.3 255.255.255.0
interface Serial0/1
 ip address 192.168.1.3 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint non-broadcast
 ip ospf priority 0
 serial restart-delay 0
 frame-relay map ip 192.168.1.1 301
 no frame-relay inverse-arp
router ospf 1
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area 0
R4:
interface Loopback0
 ip address 4.4.4.4 255.255.255.0
interface Serial0/1
 ip address 192.168.1.4 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint
 ip ospf priority 0
 serial restart-delay 0
 frame-relay map ip 192.168.1.1 401
 no frame-relay inverse-arp
router ospf 1
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area 0