How does an S series switch hide an OSPF route so that the route is not advertised to any other area

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Question: How to hide an OSPF route so that it is not advertised to any other area?
Answer: A filter list on an S series switch supporting OSPF cannot prevent a route from being advertised. You can use either of the following methods:
Configure route summarization on an ABR and specify the keyword no-advertise in the command.
Configure an ABR to filter the routes carried in Type 3 LSAs. The ABR filters routes when advertising Type 3 LSAs between OSPF areas. Only the packets with prefixes meeting requirements can be transmitted from one area to another. In this way, the incoming and outgoing packets of an area are controlled.

Other related questions:
How can an OSPF route be hidden so that it is not advertised to any other area
A filter list cannot solve this problem. You solve this problem through the following methods: Configure route summarization on the Area Border Router (ABR), specifying the no-advertise keyword in the route summarization command. Configure the filtering of OSPF ABR Type-3 LSAs. This feature extends the ABR capabilities so that an ABR can filter routes when advertising Type-3 LSAs between OSPF areas. This feature allows only packets with specified prefixes to be sent from one area to another area and restricts all packets with other prefixes. This type of area filtering can be applied out of a specific OSPF area, into a specific OSPF area, or into and out of the same OSPF areas at the same time.

Configuring OSPF to import default routes on the USG2000 series
Configure OSPF to import default routes on the USG2000 series as follows: 1. In the user view, run the system-view command to enter the system view. 2. Run the ospf [ process-id ] command to access the OSPF view. 3. Select the following configurations as required. To import a default route to the OSPF process, run the default-route-advertise [ [ always | permit ] | cost cost | type type | route-policy route-policy-name ] * command. To specify the default cost of Type-3 summary LSA, run the default-route-advertise summary cost cost command.

Configuring OSPF to import default routes on the USG6000 series
Configure OSPF to import default routes on the USG6000 series as follows: 1. In the user view, run the system-view command to enter the system view. 2. Run the ospf [ process-id ] command to access the OSPF view. 3. Select the following configurations as required. To import a default route to the OSPF process, run the default-route-advertise [ [ always | permit ] | cost cost | type type | route-policy route-policy-name ] * command. To specify the default cost of Type-3 summary LSA, run the default-route-advertise summary cost cost command.

How does OSPF on S series switches create ECMP routes
Question: Two routes learned from two areas with the same cost are not ECMP routes. Why? Answer: According to RFC 2328, OSPF can generate ECMP routes only when the following conditions are met: The routes are learned from the same area. The routes have the same priority and cost. RFC 2328 does not define selection rules of intra-area and inter-area routes for switches. When conditions of multiple routes are the same, a switch may not select the last advertised route. If routes are Type 5 external routes, the route with the largest area ID is preferentially selected, as defined in RFC 2328.

Configure the priority of an OSPF route on an S series switch
The routing protocols may share and select the routing information because a switch may run multiple dynamic routing protocols simultaneously. In this case, a priority should be set for each routing protocol. When different protocols find multiple routes to the same destination, the route discovered by the protocol with a higher priority is preferred. On an S series switch, you can run the preference command in the OSPF process view to configure the OSPF priority. Perform the following operations: 1. Run the ospf [ process-id ] command in the system view to enter the OSPF process view. 2. Run the preference [ ase ] { preference | route-policy route-policy-name } * command to configure the OSPF priority. The parameters are described as follows: ase: indicates the priority of the AS-External route. preference: indicates the OSPF route priority. A smaller value indicates a higher priority. route-policy route-policy-name: indicates the priority for specified routes in the routing policy. The default OSPF priority value is 10. When an ASE is specified, the default OSPF priority is 150. For example, set the priority of routes in OSPF process 100 to 150 as follows: [HUAWEI] ospf 100 [HUAWEI-ospf-100] preference 150

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