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 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 699 0x2 0x4e86 32
	Summary *10.0.0.0 192.168.17.1 0x80000003 289 0x2 0xe7ac 28
	Summary *10.0.0.1 192.168.17.1 0x80000002 289 0x2 0x5830 28
	Summary *10.0.1.0 192.168.17.1 0x80000007 22 0x2 0xdeaf 28
	Summary *10.0.2.0 192.168.17.1 0x80000002 289 0x2 0xd3bf 28
	Summary *10.0.16.0 192.168.17.1 0x80000002 289 0x2 0xb1c7 28
	Summary *192.168.13.1 192.168.17.1 0x80000002 289 0x2 0x9982 28
	Summary *192.168.17.1 192.168.17.1 0x80000002 289 0x2 0x68fc 28
	Summary *192.168.18.1 192.168.17.1 0x80000002 289 0x2 0xe939 28
	Summary *192.168.19.1 192.168.17.1 0x80000002 289 0x2 0xde43 28
	 OSPF AS SCOPE link state database
	 Type ID Adv Rtr Seq Age Opt Cksum Len
	Extern 0.0.0.0 192.168.15.1 0x80000001 590 0x2 0x67f1 36
	Extern 172.19.121.0 192.168.15.1 0x80000001 590 0x2 0x859a 36

With the NSSA configured, these Type 5 routes are injected into the area as Type 7 (NSSA) LSAs:

	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 0x80000002 29 0x0 0x6338 60
	Router 192.168.16.1 192.168.16.1 0x80000004 2 0x0 0xe155 84
	Router *192.168.17.1 192.168.17.1 0x80000003 1 0x0 0x6dc5 36
	Network *10.0.8.1 192.168.17.1 0x80000001 1 0x0 0x6e69 32
	Summary *10.0.0.0 192.168.17.1 0x80000001 55 0x0 0xa8e 28
	Summary *10.0.0.1 192.168.17.1 0x80000001 55 0x0 0x7813 28
	Summary *10.0.1.0 192.168.17.1 0x80000002 1 0x0 0x78e 28
	Summary *10.0.2.0 192.168.17.1 0x80000001 55 0x0 0xf3a2 28
	Summary *10.0.16.0 192.168.17.1 0x80000001 55 0x0 0xd1aa 28
	Summary *192.168.13.1 192.168.17.1 0x80000001 55 0x0 0xb965 28
	Summary *192.168.17.1 192.168.17.1 0x80000001 55 0x0 0x88df 28
	Summary *192.168.18.1 192.168.17.1 0x80000001 55 0x0 0xa1c 28
	Summary *192.168.19.1 192.168.17.1 0x80000001 55 0x0 0xfe26 28
	NSSA 0.0.0.0 192.168.15.1 0x80000001 29 0x8 0xf2e4 36
	NSSA 172.19.121.0 192.168.15.1 0x80000001 29 0x8 0x118d 36
	 OSPF AS SCOPE link state database
	 Type ID Adv Rtr Seq Age Opt Cksum Len
	Extern 0.0.0.0 192.168.15.1 0x80000001 711 0x2 0x67f1 36
	Extern 172.19.121.0 192.168.15.1 0x80000001 711 0x2 0x859a 36

The output shows that the Type 7 NSSAs still originate from the ASBR, RouterE (192.168.15.1).

As with stub areas, you can configure the ABR in the NSSA to not flood Type 3 (Network Summary) LSAs to the routers in the stub area:

	[edit protocols ospf]
	aviva@RouterJ# set area 0.0.0.3 nssa no-summaries

Looking at a router in Area 0.0.0.3, where before its link-state database would have contained Type 3 (Summary) LSAs:

	aviva@RouterE> show ospf database
	 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 429 0x0 0x4167 60
	Router 192.168.16.1 192.168.16.1 0x8000000b 7 0x0 0x94d3 72
	Router 192.168.17.1 192.168.17.1 0x80000006 8 0x0 0xd8ca 48
	Network 10.0.8.2 192.168.16.1 0x80000006 7 0x0 0xbd6 32
	Summary 10.0.0.0 192.168.17.1 0x80000002 8 0x0 0x8552 28
	Summary 10.0.1.0 192.168.17.1 0x80000002 8 0x0 0x8451 28
	Summary 10.0.2.0 192.168.17.1 0x80000002 8 0x0 0x795b 28
	Summary 192.168.18.1 192.168.17.1 0x80000001 17 0x0 0x91d3 28
	NSSA *10.0.15.0 192.168.15.1 0x80000001 429 0x8 0xcaf3 36
	NSSA *172.19.121.0 192.168.15.1 0x80000001 429 0x8 0x118d 36
	NSSA *192.168.15.1 192.168.15.1 0x80000001 429 0x8 0x91cc 36

The Summary LSAs are no longer present:

	aviva@RouterE> show ospf database
	 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 338 0x0 0x4167 60
	Router 192.168.16.1 192.168.16.1 0x80000008 283 0x0 0x9ad0 72
	Router 192.168.17.1 192.168.17.1 0x80000004 278 0x0 0xdcc8 48
	Network 10.0.8.2 192.168.16.1 0x80000004 283 0x0 0xfd4 32
	NSSA *10.0.15.0 192.168.15.1 0x80000001 338 0x8 0xcaf3 36
	NSSA *172.19.121.0 192.168.15.1 0x80000001 338 0x8 0x118d 36
	NSSA *192.168.15.1 192.168.15.1 0x80000001 338 0x8 0x91cc 36






JUNOS Cookbook
Junos Cookbook (Cookbooks (OReilly))
ISBN: 0596100140
EAN: 2147483647
Year: 2007
Pages: 290
Authors: Aviva Garrett
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