配置如下表所示：
ROUTE1#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 10.1.1.1/24, Area 0
Process ID 20, Router ID 10.1.2.1, Network Type BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 10.1.2.1, Interface address 10.1.1.1
Backup Designated router (ID) 10.1.1.2, Interface address 10.1.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
ROUTE2#show ip ospf interface serial 1/1
Serial1/1 is up, line protocol is up
Internet Address 10.1.1.2/24, Area 0
Process ID 20, Router ID 10.1.1.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.2.1
Suppress hello for 0 neighbor(s)
從上面可以看出，路由器Router1是配置broadcast模式，而路由器Roure2配置成點(diǎn)對(duì)點(diǎn)模塊。這種網(wǎng)絡(luò)類型的不匹配，導(dǎo)致了路由通告的不可達(dá)。
ROUTE1#show ip ospf database router 10.1.1.2
Adv Router is not-reachable
LS age: 418
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.1.1.2
Advertising Router: 10.1.1.2
LS Seq Number: 80000002
Checksum: 0xFA63
Length: 60
Number of Links: 3
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 10.1.2.1
(Link Data) Router Interface address: 10.1.1.2
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.1.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 64
ROUTE2#show ip ospf database router 10.1.2.1
Adv Router is not-reachable
LS age: 357
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.1.2.1
Advertising Router: 10.1.2.1
LS Seq Number: 8000000A
Checksum: 0xD4AA
Length: 48
Number of Links: 2
Link connected to: a Transit Network
(Link ID) Designated Router address: 10.1.1.1
(Link Data) Router Interface address: 10.1.1.1
Number of TOS metrics: 0
TOS 0 Metrics: 64
可以看出，對(duì)于子網(wǎng)10.1.1.0/24, 路由器ROUTE2產(chǎn)生一個(gè)點(diǎn)對(duì)點(diǎn)連接，而路由器Router2則產(chǎn)生一個(gè)透過的連接，這就在鏈路狀態(tài)數(shù)據(jù)庫中產(chǎn)了不一致，從而導(dǎo)致路由信息不會(huì)出現(xiàn)在路由表中。
ROUTE2#show ip route
10.1.0.0/16 is variably subnetted, 3 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Serial1/1
C 10.1.3.1/32 is directly connected, Loopback0
解決方案：
為了解決這個(gè)問題，需要將兩邊的網(wǎng)絡(luò)類型配置為一致。既可以將Router1上的網(wǎng)絡(luò)類型改為點(diǎn)對(duì)點(diǎn)，也可以將Router2上的網(wǎng)絡(luò)類型改為broadcast.在這個(gè)例子中我們將Router1上的網(wǎng)絡(luò)類型修改為點(diǎn)對(duì)點(diǎn)類型。
ROUTE1#configure terminal
ROUTE1(config)#interface serial 1
ROUTE1(config-if)#no ip ospf network broadcast
ROUTE1(config-if)#end
ROUTE1#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 10.1.1.1/24, Area 0
Process ID 20, Router ID 10.1.2.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.2
Suppress hello for 0 neighbor(s)
至此，故障排除。
需要注意的是，如果有一端的接口是多接口，而另一端是子接口，那么需要將兩邊都修改為broadcast接口。
實(shí)例二、一端Unnumbered另一端Numbered
配置如下表：
ROUTER1#show interface serial 1
Serial1 is up, line protocol is up
Hardware is cxBus Serial
Interface is unnumbered. Using address of Loopback0 (10.1.2.1)
ROUTER2#show interface serial 1/1
Serial1/1 is up, line protocol is up
Hardware is cxBus Serial
Internet address is 10.1.1.2/24
上面的輸出顯示出ROUTER1的Serial 1接口是個(gè)unnumbered 接口，使用Loopback0的地址,而ROUTER2的Serial 1/1則配置有IP地址。
ROUTER1#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 0.0.0.0/24, Area 0
Process ID 20, Router ID 10.1.2.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.2
Suppress hello for 0 neighbor(s)
ROUTER2#show ip ospf interface serial 1/1
Serial1/1 is up, line protocol is up
Internet Address 10.1.1.2/24, Area 0
Process ID 20, Router ID 10.1.1.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.2.1
Suppress hello for 0 neighbor(s)
從上面可以看出，兩邊的網(wǎng)絡(luò)類型都是點(diǎn)對(duì)點(diǎn)的，出現(xiàn)問題的原因是一邊是unnumbered 而另一邊則配置有IP地址，這就造成了OSPF數(shù)據(jù)庫中的不一致。
ROUTER1#show ip ospf database router 10.1.1.2
Adv Router is not-reachable
LS age: 418
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.1.1.2
Advertising Router: 10.1.1.2
LS Seq Number: 80000002
Checksum: 0xFA63
Length: 60
Number of Links: 3
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 10.1.2.1
(Link Data) Router Interface address: 10.1.1.2
Number of TOS metrics: 0
TOS 0 Metrics: 64
ROUTER2#show ip ospf database router 10.1.2.1
Adv Router is not-reachable
LS age: 357
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.1.2.1
Advertising Router: 10.1.2.1
LS Seq Number: 8000000A
Checksum: 0xD4AA
Length: 48
Number of Links: 2
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 10.1.1.2
(Link Data) Router Interface address: 0.0.0.4
Number of TOS metrics: 0
TOS 0 Metrics: 64
可以看見ROUTER1為這個(gè)點(diǎn)到點(diǎn)鏈路產(chǎn)生了一個(gè)包括它的接口地址信息的LSA，而Router2同樣產(chǎn)生了一個(gè)包括IfIndex值的LSA，這就在鏈路狀態(tài)數(shù)據(jù)庫中產(chǎn)生了不一致，也就意味著路由信息不會(huì)在路由表中出現(xiàn)。從以下的命令可以看到：
ROUTER2#show ip route
10.1.0.0/16 is variably subnetted, 3 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Serial1/1
C 10.1.3.1/32 is directly connected, Loopback0
解決辦法：
要解決這個(gè)問題，可以將兩邊路由器都楝配為unnumbered的，或者為兩連路由器的接口都配置上IP地址。在這個(gè)例子中我們把Router1的serial1口配置上IP地址。
ROUTER1#configure terminal
ROUTER1(config)#interface serial 1
ROUTER1(config-if)#no ip unnumbered loopback 0
ROUTER1(config-if)#ip address 10.1.1.1 255.255.255.0
ROUTER1)#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 10.1.1.1/24, Area 0
Process ID 20, Router ID 10.1.2.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.2
Suppress hello for 0 neighbor(s)
ROUTER2#show ip route
10.1.0.0/16 is variably subnetted, 3 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Serial1/1
O 10.1.2.1/32 [110/65] via 10.1.1.1, 00:03:08, Serial1/1
C 10.1.3.1/32 is directly connected, Loopback0
至此，問題解決。
