sybex书的135页的一个实验：
我照着他的配置去配，但是最后发现D不能到达A，当我在Routerc上的router ospf 24中加入这句：redistribute rip subnet后，D 就可以到达A 了，我看了一下前后的d的路由表是一样的，请问为什么呢？RouterA
interface Ethernet0
ip address 10.1.1.1 255.255.255.0
!
interface Ethernet1
ip address 10.1.2.1 255.255.255.0
!
router ospf 24
network 10.0.0.0 0.255.255.255 area 0
RouterB
interface Ethernet0
ip address 10.1.2.2 255.255.255.0
!
interface Ethernet1
ip address 1.1.1.1 255.255.255.0
!
router ospf 24
network 10.0.0.0 0.255.255.255 area 0
network 1.0.0.0 0.255.255.255 area 1
area 0 range 10.0.0.0 255.255.0.0
area 1 nssa
RouterC
interface Ethernet0
ip address 1.1.1.2 255.255.255.0
!
interface Ethernet1
ip address 172.16.1.1 255.255.255.0
!
router ospf 24
redistribute rip
network 1.0.0.0 0.255.255.255 area 1
default-metric 128
area 1 nssa
!
router rip
redistribute ospf 24
network 172.16.0.0
default-metric 3
RouterD
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Ethernet1
ip address 172.16.2.1 255.255.255.0
!
router rip
network 172.16.0.0
RouterD的路由表：
Gateway of last resort is not set
R 1.0.0.0/8 [120/3] via 172.16.1.1, 00:00:02, Ethernet0
R 10.0.0.0/8 [120/3] via 172.16.1.1, 00:00:02, Ethernet0
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Ethernet0
C 172.16.2.0 is directly connected, Loopback1