Cisco OSPF N1 和 N2 路由配置场景

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OSPF N1 and N2 Routes: Configuration Scenario

Introduction to OSPF Routes

OSPF路由介绍

Before discussing OSPF N1 and N2 routes, it is essential to understand OSPFroutes.
在讨论 OSPF N1 和 N2 路由之前，必须了解 OSPF 路由。

OSPF external routes in a normal area would appear as either E1 routes or E2 routes. By default when we configure the redistribution of external routes in an OSPF area the route type for the external network is E2 which appear as OE2 in the routing table.
正常区域中的 OSPF 外部路由将显示为 E1 路由或 E2 路由。默认情况下，当我们在 OSPF 区域配置外部路由的重新分发时，外部网络的路由类型为 E2，在路由表中显示为 OE2。

E1 are the route when the cost of the internal links is taken into consideration for SPF calculation.
E1 是将内部链接的成本考虑在 SPF 计算中的路由。
E2 are the routes which take only the external link cost into the SPF calculation.
E2 是仅将外部链接成本纳入 SPF 计算的路由。

OSPF N1 and N2 Routes

OSPF N1 和 N2 路由
OE1 or OE2 both are represented by LSA type 5 in the OSPF database. Now in a special OSPF area, NSSA or Totally NSSA the LSA type 5 cannot be propagated. Hence a new LSA type 7 is propagated in these areas by the respective ABR for that area. In the routing table of routers in NSSA OSPF areas the external routes instead of appearing as OE1 or OE2 routes would appear as OSPF N1 and N2 routes (i.e. ON1 route or ON2 route). ON1 routes are very similar to OE1 routes and ON2 are similar to OE2. Default metric for OE2 and ON2 routes are 20.
OE1 或 OE2 在 OSPF 数据库中都用类型为 5 的 LSA 表示。在特定的 OSPF 区域内，不能传播类型为 5 的 LSA NSSA 或 Totally NSSA。因此，一个新的 LSA 类型 7 将由该区域的相应 ABR 在这些区域中传播。在 NSSA OSPF 区域内路由器的路由表中，外部路由不再以 OE1 或 OE2 形式出现，而是以 OSPF N1 和 N2 形式出现 (即 ON1 路由或 ON2 路由)。ON1 路由与 OE1 非常相似，ON2 路由与 OE2 非常相似。OE2 和 ON2 路由的缺省度量值是 20

We will check all these OE1 and OE2 in the topology below –
我们将在下面的拓扑中检查所有这些 OE1 和 OE2 –

In the topology above the route for 9.9.0.6 will be redistributed from EIGRP domain to OSPF area 20 which is NSSA area on router R5 acting as the ASBR. This type 7 LSA (ON2) on reaching the router R3 is converted to Type 5 LSA (OE2) and is propagated to area 0 and area 10 there onwards.
在上面的拓扑中，9.9.0.6 的路由将从 EIGRP 域重新分发到 OSPF 区域 20，即充当 ASBR 的路由器 R5 上的 NSSA 区域。该 7 型 LSA （ON2）在到达路由器 R3 时被转换为 5 型 LSA （OE2)，并从那里传播到区域 0 和区域 10。

Output (OSPF N1 and N2 routes)

输出（OSPF N1 和 N2 路由）
On R4 we see the route for external subnet appears as N2 route by default. If we need to modify the default behaviour and have N1 route then we need to specifically mention that as the time of redistribution of EIGRP in OSPF on router R5.
在 R4 上，我们看到外部子网的路由默认显示为 N2 路由。如果我们需要修改默认行为并具有 N1 路由，那么我们需要特别提到它在路由器 R5 上的 OSPF 中重新分配 EIGRP 的时间。

R4# sh ip route | i N2

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
O N2  9.9.0.6/32 [110/20] via 9.9.45.5, 00:00:51, FastEthernet1/0
O N2  9.9.56.0/24 [110/20] via 9.9.45.5, 00:00:51, FastEthernet1/0

On R1 and R2 if we see route for 9.9.0.6 appears as OE2 route as R3 has converted the type 7 LSA to type 5 LSA.
在 R1 和 R2 上，如果我们看到 9.9.0.6 的路由显示为 OE2 路由，因为 R3 已将类型 7 LSA 转换为类型 5 LSA。

R1#sh ip route | i E2

E1 – OSPF external type 1, E2 – OSPF external type 2
O E2  9.9.0.6/32 [110/20] via 9.9.13.3, 00:03:31, FastEthernet1/0
O E2  9.9.56.0/24 [110/20] via 9.9.13.3, 00:03:31, FastEthernet1/0

R2# sh ip route | i E2

 E1 – OSPF external type 1, E2 – OSPF external type 2
O E2  9.9.0.6/32 [110/20] via 9.9.12.1, 00:03:56, FastEthernet0/0
O E2  9.9.56.0/24 [110/20] via 9.9.12.1, 00:03:56, FastEthernet0/0

On adding the below command on R5 at time of redistribution
在重新分发时在 R5 上添加以下命令时

R5(config-router)#redistribute eigrp 10 subnets metric 10 metric-type 1

Now we will be able to see the route for external subnets as ON1 and OE1.
现在，我们将能够将外部子网的路由视为 ON1 和 OE1。

R4#sh ip route | i N1

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
O N1  9.9.0.6/32 [110/11] via 9.9.45.5, 00:00:59, FastEthernet1/0
O N1  9.9.56.0/24 [110/11] via 9.9.45.5, 00:00:59, FastEthernet1/0

R2#sh ip route | i E1

E1 – OSPF external type 1, E2 – OSPF external type 2
O E1  9.9.0.6/32 [110/14] via 9.9.12.1, 00:01:34, FastEthernet0/0
O E1  9.9.56.0/24 [110/14] via 9.9.12.1, 00:01:34, FastEthernet0/0

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