路由重分命令 redistribute ospf 1和 redistribute ospf 1 metric x的区别

redistribute ospf 1和 redistribute ospf 1 metric x 这两条命令看着基本都是相同的，都是把ospf路由重分布；在对端端的路由器看到路由信息不一样呢？
拓扑如下



R1 OSPF配置：
router ospf 1
log-adjacency-changes
network 1.1.1.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0

R2 OSPF配置：
router ospf 1
log-adjacency-changes
network 2.2.2.0 0.0.0.255 area 1
network 192.168.2.0 0.0.0.255 area 1

R3 OSPF/RIP配置：
router ospf 1
log-adjacency-changes
redistribute rip metric 2 subnets
network 192.168.1.0 0.0.0.255 area 0
network 192.168.2.0 0.0.0.255 area 1
!
router rip
version 2
redistribute ospf 1
network 3.0.0.0
network 192.168.3.0
no auto-summary
!

R4 RIP配置：
router rip
version 2
network 4.0.0.0
network 192.168.3.0
no auto-summary

R4的路由学习：
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

3.0.0.0/24 is subnetted, 1 subnets
R 3.3.3.0 [120/1] via 192.168.3.3, 00:00:20, Ethernet0/3
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback4
R 192.168.1.0/24 [120/1] via 192.168.3.3, 00:00:20, Ethernet0/3
R 192.168.2.0/24 [120/1] via 192.168.3.3, 00:00:20, Ethernet0/3
C 192.168.3.0/24 is directly connected, Ethernet0/3

比较奇怪的是：R4上能够学习OSPF重分到RIP中的物理接口的路由信息而学习不到loopback的路由信息。
如果把R3上的ospf重分布到RIP中的路由增加metric x 之后 R4就能够学习到loopback的路由信息
R4的路由信息：
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 192.168.3.3, 00:00:12, Ethernet0/3
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 192.168.3.3, 00:00:12, Ethernet0/3
3.0.0.0/24 is subnetted, 1 subnets
R 3.3.3.0 [120/1] via 192.168.3.3, 00:00:12, Ethernet0/3
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback4
R 192.168.1.0/24 [120/1] via 192.168.3.3, 00:00:12, Ethernet0/3
R 192.168.2.0/24 [120/1] via 192.168.3.3, 00:00:13, Ethernet0/3
C 192.168.3.0/24 is directly connected, Ethernet0/3

请各位看官，谁能够解释一下 redistribute ospf 1和redistribute ospf 1 metric x
的区别？
个人理解：

如果后面的metric值不配置的话表示带的其他相应参数的默认值，如果想对默认值修改才会带相应的参数并予以赋值。
如rip路由重分布到OSPF路由当中：redistribute rip subnets 默认是外部的路由的metric是20， OSPF external type 默认是E2

或许有另外一种情况是模拟器的IOS的问题，请各位大大们解释一下。

附件：http://down.51cto.com/data/2368421