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This article will explain in detail how to fully configure NSSA in OSPF. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

Application scenarios:

When designing the network, we want to minimize advertisements and routing entries in area 2, but we also need to let R3 act as ASBR, sending routing information from external autonomous systems to other areas.

This requirement fully meets the application of NSSA (non-pure stub area). LSA4 LSA5 will be blocked in the NSSA area, and only receive more notifications such as LSA7 than the stub area, that is, the notification sent by R3 to the external autonomous area.

Configuration:

Configure the conditions according to the schematic diagram (completed in Xiaofan)

Ip address and so on are not explained much.

On R1:

Router (config) # router os 1

Router (config-router) # net 10.0.0.0 0.255.255.255 ar 0 (only one is declared regardless of other interfaces on R1)

On R2:

Router (config) # router os 1

Router (config-router) # net 10.0.0.0 0.255.255.255 ar 0

Router (config-router) # net 20.0.0.0 0.255.255.255 ar 2

On R3, you only need to declare the network segment of the interface in area2, and only configure IP for the external interface.

Router (config) # router os 1

Router (config-router) # net 20.0.0.0 0.255.255.255 ar 2

There is no need to declare routing information on R4, only a default route is needed because this is not a router in this AS.

Router (config) # ip route 0.0.0.0 0.0.0.0 30.0.0.1

At this time, the ping on R4 does not reach R1, because there is no route on R3 to distribute the 30.0.0.0 segment.

But if it is distributed now, R3 will be the same as a normal ASBR, and area 2 will accept advertisements of type 4 and 5 like other ordinary area, and the routing table will not be reduced.

Next, configure NSSA.

On R3:

Router (config-router) # area 2 nssa (set area 2 to the NSSA area)

On R2:

Router (config-router) # area 2 nssa

Then redistribute the 30.0.0.0 network segment on R3:

Router (config-router) # redistribute connected metric 10 subnets (the explanation of this sentence was described in detail in the previous article)

At this point, there will be a NSSA announcement from the LSA7 sent by R3 on R2:

Beginning with O N2:

This is the working principle and configuration of NSSA.

This is the end of this article on "how to fully configure NSSA in OSPF". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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