首先看拓扑：

一个面试考官问我一个这样的问题，拓扑如上，为什么R1上的lo0 PING 不通 R6 上的lo0,说是一切都按正常配置，说是考我EIGRP的特性。我当然很纳闷，如果都正常配置怎么会不通呢，最后他告诉我主要是考我，EIGRP的域内管理距离是90，域外管理距离是170。当时可能不够自信也没多想，回来后越想越不对，一般来说，只有到达目的地有两条路由的时候才会考虑管理距离，但这里没有这个情况啊，于是自已设计了一个实验加以验证，结果是，可以通。

R3 与 R5  R4与R5 使用帧中继相连，DLCI号分别为：305 503 405 504

帧中继只能用点到点子接口。

主要配置如下：

R1：

interface Loopback0
 ip address 1.1.1.1 255.255.255.0

interface Serial1/1
 ip address 10.10.12.1 255.255.255.252

router rip
 version 2
 network 1.0.0.0
 network 10.0.0.0
 no auto-summary

R2：

interface FastEthernet0/0
 ip address 10.10.24.1 255.255.255.252
 duplex half
!
interface Serial1/0
 ip address 10.10.12.2 255.255.255.252
 serial restart-delay 0
 clock rate 64000

router eigrp 1
 redistribute rip metric 10000 100 255 1 1500
 network 10.10.23.0 0.0.0.255
 network 10.10.24.0 0.0.0.255
 no auto-summary
!
router rip
 version 2
 redistribute eigrp 1 metric 2
 network 10.0.0.0
 no auto-summary

R3：

interface Serial1/0
 ip address 10.10.23.2 255.255.255.252
 serial restart-delay 0
!

interface Serial1/2
 ip address 10.10.35.1 255.255.255.252
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.10.35.2 305 broadcast   //静态映射，DLCI号是帧中继交换分配置的，如果不配置就不通。

no frame-relay inverse-arp //静态映射要关闭反向ARP

router eigrp 1
 network 10.10.23.0 0.0.0.255
 network 10.10.35.0 0.0.0.255
 no auto-summary
!

R4：

interface FastEthernet0/0
 ip address 10.10.24.2 255.255.255.252
 duplex half

interface Serial1/2
 ip address 10.10.45.1 255.255.255.252
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.10.45.2 405 broadcast
 no frame-relay inverse-arp

router eigrp 1
 network 10.10.24.0 0.0.0.255
 network 10.10.34.0 0.0.0.255
 network 10.10.45.0 0.0.0.255
 no auto-summary

R5：

interface Serial1/1
 ip address 10.10.56.1 255.255.255.252
 serial restart-delay 0

interface Serial1/2.1 point-to-point
 ip address 10.10.45.2 255.255.255.252
 frame-relay interface-dlci 504  
!
interface Serial1/2.2 point-to-point
 ip address 10.10.35.2 255.255.255.252
 frame-relay interface-dlci 503

router eigrp 1
 redistribute ospf 100 metric 10000 100 255 1 1500
 network 10.10.35.0 0.0.0.255
 network 10.10.45.0 0.0.0.255
 no auto-summary
!
router ospf 100
 log-adjacency-changes
 redistribute eigrp 1 subnets   //默认为TYPE 2，cost 为20
network 10.10.56.0 0.0.0.255 area 0

R6：

interface Serial1/0
 ip address 10.10.56.2 255.255.255.252
 serial restart-delay 0

router ospf 100
 log-adjacency-changes
 network 6.6.6.0 0.0.0.255 area 0
 network 10.10.56.0 0.0.0.255 area 0

结果测试：R1 PING R6

R1#ping 6.6.6.6 so 1.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 6.6.6.6, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/92/132 ms
R1#

R6 PING R1

R6#ping 1.1.1.1 so 6.6.6.6

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 6.6.6.6
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 84/102/120 ms
R6#