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JUNOS Cookbook by Aviva Garrett

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12.7. Creating a Not-So-Stubby Area

Problem

You want to configure a stub area for an area that has an ASBR to connect it to an external network. This area already sends AS External LSAs to the backbone area and doesn't need to receive them from the backbone.

Solution

Configure the area as an NSSA. Include this configuration on each router in the NSSA area.

	[edit protocols ospf]
	aviva@RouterJ# set area 0.0.0.3 nssa

Discussion

The configuration for NSSA is similar to that for stub areas. Include the nssa statement when configuring each area. Once you commit the configuration, you can see that the router is in an NSSA:

	aviva@RouterJ> show ospf interface fe-0/0/1.0 detail
	Interface                 State     Area      DR ID         BDR ID      Nbrs
	fe-0/0/1.0                BDR      0.0.0.3   192.168.16.1  192.168.17.1    1
	Type: LAN, Address: 10.0.8.1, Mask: 255.255.255.240, MTU: 1500, Cost: 1
	DR addr: 10.0.8.2, BDR addr: 10.0.8.1, Adj count: 1, Priority: 128
	Hello: 10, Dead: 40, ReXmit: 5, Stub NSSA
	Auth type: None

Before you configure the stub area, the OSPF link-state database contains two Type 5 (AS External) LSAs for the external routes that are coming from the ASBR, which is RouterE (192.168.15.1):

	aviva@RouterJ> show ospf database area 0.0.0.3 OSPF link state database, area 0.0.0.3 Type ID Adv Rtr Seq Age Opt Cksum Len Router 192.168.15.1 192.168.15.1 0x80000004 163 0x2 0x4156 60 Router 192.168.16.1 192.168.16.1 0x80000007 49 0x2 0xbd74 84 Router *192.168.17.1 192.168.17.1 0x80000004 290 0x2 0x47ea 36 Network *10.0.8.1 192.168.17.1 0x80000002 ...

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