OSPF与ISIS的双向重分布

　　如圖所示：OSPF與ISIS在路由器Lajoie上雙向重分布。

　　配置很簡單：

　　router ospf 100

　　redistribute i sis level-1-2 metric-type 1 subnets

　　network 172.20.11.0 0.0.0.255 area 0

　　!

　　router isis

　　net 00.0002.0020.0200.6006.00

　　redistribute ospf 100 metric

　　is-type level-2-only

　　metric-style wide

　　!

　　interface Ethernet1/0

　　ip address 172.20.10.1 255.255.255.0

　　ip router isis

　　isis circuit-type level-2-only

　　!

　　然後，在Morgan及Collins上檢查路由表，問題出現了……

　　Morgan上show ip route，看到有172.20.20.0/24的路由(Collins上的接口網段)，從Lajoie學到，ISIS重分布入OSPF所得。

　　但Morgan的路由表裡沒有172.20.10.0/24，而172.20.10.0/24正是ASBR Lajoie上啟用ISIS的接口。重分布沒有將這個接口的網段帶入OSPF。

　　再看Collins上的路由表，172.20.33.192/26，172.20.35.0/24，172.20.34.48/28這三個網段都在。但少了172.20.11.0/24這個網段，該網段是ASBR咝蠴SPF的接口地址所在網段。

　　是不是可以下結論，OSPF與ISIS雙向重分布時，不會將OSPF或ISIS的直連接口一起重分布。

　　解決上述問題的方法就是：

　　在ASBR上，將咝蠴SPF的直連接口，重分布入ISIS：

　　router isis

　　net 00.0002.0020.0200.6006.00

　　redistribute connected route-map CONN_TO_ISIS

　　redistribute ospf 100 metric

　　is-type level-2-only

　　metric-style wide

　　!

　　route-map CONN_TO_ISIS permit 10

　　match interface Ethernet0/0

　　!

　　將咝蠭SIS的直連接口，重分布入OSPF：

　　router ospf 100

　　redistribute connected metric-type 1 subnets route-map CONN_TO_OSPF

　　redistribute isis level-1-2 metric-type 1 subnets

　　network 172.20.11.0 0.0.0.255 area 0

　　!

　　route-map CONN_TO_OSPF permit 10

　　match interface Ethernet1/0

　　!

　　CISCO.COM上有一個CASE 說的也是這個問題：

　　http://www.ciscotaccc.com/iprout/showcase?case=K11552379

　　Core Issue:

　　Route redistribution is used to propagate routes learned using one protocol into another routing protocol. When Intermediate System-to-Intermediate System (IS-IS) is redistributed into Open Shortest Path First (OSPF), some IS-IS routes may not be redistributed successfully. Specifically, routes advertised using IS-IS on the redistributing router are not redistributed. This behavior is expected. If a directly connected network is also advertised by IS-IS, the route is entered into the local routing table as a connected route and not as an IS-IS route. While redistributing IS-IS into OSPF, these directly connected routes are not injected into OSPF.　

　　Resolution:

　　To redistribute connected routes, marked as C in the routing table, perform these steps:

　　Configure an OSPF routing process by issuing the router ospf command.

　　Redistribute the connected routes into OSPF by issuing the redistribute connected command.