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ISCOM2600G-HI (A) Series Configuration Guide
Backbone area
After OSPF divides areas, not all areas are equal. A special area with area ID as 0 is called the
backbone area. The backbone area transmits inter-area routes. Routing information from non-
backbone area must be forwarded by the backbone area. The backbone area has the following
information:
Stub area
The border router has low performance, so its routing table must be limited. Configuring the
Stub area is used to prevent external LSAs from entering the area to the minimum extend.
In the Stub area, only Type1, Type2, and Type3 LSAs are advertised, and Type5 LSAs are not
allowed to enter, which reduces the size of the routing table and the number of transmitted
routes. In addition, you can configure the area to Totally Stub area which allows Type1 and
Type2 LSAs and a default Type3 LSA. This further reduces the size and the number. In the
Totally Stub area, the ABR does not transmit inter-area routes and external routes to the area.
Not each area complies with the (Totally) Stub area. Generally, the (Totally) Stub area is at the
border of an AS. To make routes from other areas to the AS or external routes of the AS
reachable, the ABR generates a default route, and advertises it to non-ABR routers in the area.
Route types
OSPF divides routes into four types by priority in descending order: Intra Area route, Inter
Area route, Type1 External route, and Type2 External route.
The Intra Area route and Inter Area route describe network topology of the AS. External
routes describe how to choose the route to a destination address out of the AS. Whether to
calculate interval path cost of AS makes OSPF divide external routes into Type1 External
route or Type2 External route.
OSPF takes Type 1 External route with high credibility, so it chooses Type1 External route
when Type 1 External route and Type2 External route for the same destination address co-
exist regardless of the costs of these two routes.
5.7.2 Configuring basic functions of OSPF
Configure basic functions of OSPF for the ISCOM2600G-HI series switch as below.
1
2
All non-backbone areas must be interconnected with the backbone area.
The backbone area must be internally interconnected.
Cost of Type1 External route = cost from the local router to the corresponding ASBR +
cost from the ASBR to the destination address of the route
Cost of Type2 External route = cost from the ASBR to the destination address of the
route
Step
Raisecom#config
Raisecom(config)#router ospf
process-id
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Command
router-id
[ router-id
Description
Enter global configuration mode.
Start OSPF process, and enter
]
OSPF configuration mode.
5 IP services
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