拓扑如下：
R1:
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.
0
ip ospf network point-to-point
ip ospf 1 area 0
!
router ospf 1
R2:
interface FastEthernet0/0
ip address 12.1.1.60 255.255.255.
128
ip ospf network point-to-point
ip ospf 1 area 0
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
ip ospf 1 area 0
!
router ospf 1
结论：
R1与R2 的掩码不同，但OSPF的网络类型为P-to-P或者P-to-MP的话可以正常建立邻居也可以正常
如果网络类型为Broadcast即要选举DR的话就不能建立邻居,因为会产生2类LSA，而2类LSA的内容就是描述掩码的，不一致的话不能建立邻居
拓扑不变
R1:
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.0
ip ospf network
broadcast
ip ospf 1 area 0
R2:
interface FastEthernet0/0
ip address 12.1.1.60 255.255.255.0
ip ospf network
point-to-point
ip ospf 1 area 0
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
ip ospf 1 area 0
!
结论：
如果两边的网络类型不一致，可以建立邻居但不会传递LSA信息