Principles of OSPF stub and NSSA regions

Source: Internet
Author: User

Principles of the OSPF stub and NSSA regions: the ospf stub is a peripheral region. When an OSPF region is at the boundary of the autonomous system, it does not include other routing protocols, in this case, you can configure the OSPF Stub area. After the OSPF Stub area is configured, the router in the Stub area adds a default route entry to the ABR. After the full peripheral area is configured on the ABR (totally stub ), in addition to the direct connection route entry, the route entries of other vrouters in the peripheral area only have one default route entry to reach the ABR. The route entries of other regions are not learned, data packets from other regions are forwarded through the API. This reduces the route entries of other routers in the peripheral region and improves the performance of the router. Because the stub region cannot transmit five types of LSA, it means the ASE route outside the region (outside the autonomous system) it cannot be passed to stub, And the ASE route in the region cannot be passed or learned by other regions.
However, OSPF is configured on all routers in a network, but static routing or other routing protocols are not used. For example, the access server used by the user for dial-up Internet access needs to connect to the Internet on the router. However, generally, the access server does not support (and does not need to) OSPF protocol, but uses static routing to implement routing. In many cases, the ISP uses Static Routing when connecting to the user-side router for the sake of confidentiality or ease of management. -- In this case, the STUB region has very few applicable conditions. It can be said that it does not exist.
About NSSA: in order to compensate for the defects and generate the NSSA region, The NSSA region does not allow Class 5 LSA to be passed in the region, but does allow Class 7 LSA to be passed in the region class, seven types of LSA are generated when nssa introduces ASE routing, and seven types of LSA are converted to five types of LSA and transferred to other regions on the ABR, this removes the restrictions of STUB on two-way ASE propagation (out-of-region, and out-of-region), and changes to one-way restriction (out-of-region, area ). NSSA configuration: area-id nssa [default-information originate] [no-redistribute] [no-summary] area-id: Region id of the region to be configured as NSSA. Parameters in "[]" take effect only when the vroabr is an API. The keyword default-information originate is used to generate the default Type-7 LSA. After this parameter is applied, the default route exists in the ABR no matter whether the routing table exists, the default Type-7 LSA route is generated. In the ASBR table, the default route exists to generate the default Type-7 LSA route. Application: When you want to configure the NSSA region (not the totally NSSA region), by default, the ABR will not automatically generate the default route and pass it to The NSSA region, you must configure this command on the ABR router. Otherwise, you cannot reach the ASE route in other regions. If there is no ASE route in other regions, you do not need to use this command. The no-redistristrikeyword is used on ASBR and ABR, so that the routes introduced by OSPF through the redistribute command are not advertised to the NSSA region. Application:

This command can be used on R2, otherwise, the re-distribution of ASE routes will be transmitted using LSA 7 In The nssa region. Therefore, this command is used when the vro is ABR and ASBR. To further reduce the number of link status releases (LSA) sent to The NSSA region, you can configure the no-summary attribute on the ABR, disable ABR from sending summary_net LSAs (Type-3 LSA) To The NSSA region ). After this parameter is configured, the ABR filters out lsa of the Type3 type, that is, routes between regions are not displayed in the NSSA region, and the route table is further streamlined. Since there are default routes, there is no need for other specific routes pointing outside the region, because nssa has 7 types of LSA, so there is an ASE route. when data is sent to other regions of OSPF, it will arrive through the default route. This parameter is recommended. (This configuration is the totally nssa region ). If the vro is only a vro in a region, you only need to configure area-id nssa. If it is an API, add three optional parameters as needed.

Author zm881225

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