Advanced Juniper Networks Routing
Release 5.1, Revision 0
Module 3: OSPF NSSA
Copyright © 2001, Juniper Networks, Inc.
Module Objectives
 Review the basic components of the OSPF Protocol
 Discuss the OSPF neighbor hello protocol and
adjacency formation process
 Examine the function of the Link-State Database
(LSDB) and how it contributes routes to the routing
table
 Look at the different kinds of OSPF packet types
 Configure OSPF on a Juniper Networks router
Copyright © 2001, Juniper Networks, Inc.
LSA Flooding: Default
Area 0
LSA 1
Area 0
LSA 2
Area 1
LSA 2
Area 0
Area 0
LSA 3
LSA 4
Area 2
Area 3
LSA 3
LSA 4
Area 3
Area 0
LSA 3
LSA 5
Area 3
LSA 5
Area 1
External
Routes
Area 0
LSA 5
Area 3
LSA 5
Area 1
LSA 3
Area 1
LSA 1
Backbone
(0.0.0.0)
Area 2
LSA 3
Area 3 Area 3
LSA 3 LSA 4
Area 2
LSA 1
Area 3
LSA 1
Area 3
LSA 2
Area 0
Area 0
LSA 3
LSA 4
Area 1
Area 0
LSA 3
LSA 5
Area 2
LSA 3
Area 3
LSA 5
Area 2
LSA 2
Area 0
LSA 3
Area 1
LSA 3
Area 3
LSA 3
Area 0
LSA 4
Area 3
LSA 4
Area 0
LSA 5
Area 3
LSA 5
Area 2
External
Routes
Copyright © 2001, Juniper Networks, Inc.
Area 3
OSPF Not-So-Stubby Areas
 Allows a stub area to contain external routing
information from a local ASBR
– ASBR injects Type 7 LSAs into NSSA
– ABR converts Type 7 to Type 5 and floods into backbone
 Reachability for other external routes is via a 0/0
default route injected by the ABR
– Manual configuration step for administrator control
 Virtual links can’t transit a NSSA
Copyright © 2001, Juniper Networks, Inc.
LSA Flooding: NSSA
Area 0
LSA 1
Area 0
LSA 2
Area 1
LSA 2
Area 0
LSA 3
Area 2
LSA 3
Area 3
LSA 3
Area 2
LSA 3
Area 0
LSA 5
Area 3 Area 3
LSA 3 LSA 4
Area 2
LSA 1
Area 3
LSA 1
Area 3
LSA 2
Area 0
LSA 3
Area 1
LSA 3
Area 2
LSA 3
Area 3
LSA 7
Area 2
LSA 2
Area 0
LSA 3
Area 1
LSA 3
Area 3
LSA 3
Area 1
Stub
External
Routes
Area 3
LSA 5
Area 1
LSA 3
Area 1
LSA 1
Backbone
(0.0.0.0)
Area 0
LSA 4
Area 3
LSA 4
Area 0
LSA 5
Area 3
LSA 5
Area 2
External
Routes
Copyright © 2001, Juniper Networks, Inc.
Area 3
NSSA
OSPF NSSA No-Summaries
 Behaves like a stub no-summaries area
– ABR does not inject Type 3 LSA from backbone into area
– ASBR injects Type 7 LSAs into NSSA
– ABR converts Type 7 to Type 5 and floods into backbone
 Reachability for other external routes is still via a 0/0
default route injected by the ABR
– Again, a manual configuration step for administrator control
 Virtual links can’t transit a no-summaries NSSA
Copyright © 2001, Juniper Networks, Inc.
LSA Flooding: NSSA No-Summaries
Area 0
LSA 1
Area 0
LSA 2
Area 1
LSA 2
Area 0
LSA 3
Area 2
LSA 3
Area 3
LSA 3
Area 2
LSA 3
Area 0
LSA 5
Area 3 Area 3
LSA 3 LSA 4
Area 2
LSA 1
Area 3
LSA 1
Area 2
LSA 2
Area 0
LSA 3
Area 1
LSA 3
Area 3
LSA 3
Area 1
Stub
External
Routes
Area 3
LSA 5
Area 1
LSA 3
Area 1
LSA 1
Backbone
(0.0.0.0)
Area 0
LSA 4
Area 3
LSA 4
Area 0
LSA 5
Area 3
LSA 5
Area 2
Area 3
LSA 2
Area 3
LSA 7
External
Routes
Copyright © 2001, Juniper Networks, Inc.
Area 3
NSSA
No-Summaries
NSSA Configuration
 Each router in the area is required to configure itself
as a NSSA router
 The ABR can optionally inject a default route via the
default-metric command
– Within the default-lsa configuration hierarchy
[edit protocols ospf area 0.0.0.1]
user@area-1-router# show
nssa;
interface so-0/0/0.0;
[edit protocols ospf area 0.0.0.1]
user@area-1-abr# show
nssa {
default-lsa default-metric 10;
}
interface so-0/1/1.0;
Copyright © 2001, Juniper Networks, Inc.
NSSA No-Summaries Configuration
 Only the ABR is required to configure itself to support
a no-summaries area
 The ABR can optionally inject a default route via the
default-metric command
– Within the default-lsa configuration hierarchy
 Default is a Type 3 LSA by default with no-summaries
– Can be a Type 7 LSA with the type-7 keyword
[edit protocols ospf]
user@area-1-abr# show
area 0.0.0.1 {
nssa {
default-lsa {
default-metric 10;
type-7;
}
no-summaries;
}
interface so-0/1/1.0;
}
Copyright © 2001, Juniper Networks, Inc.
Area-Range
 All ASBR Type 7 routes are forwarded to the backbone
by default
 To summarize routing information, use the arearange command within the NSSA configuration
 A Type 5 LSA will be injected into the backbone
 Configured on the ABR only
[edit protocols ospf]
user@host# set area 1 nssa area-range 192.168.16/20
[edit protocols ospf]
user@host# show
area 0.0.0.1 {
nssa {
default-lsa default-metric 10;
area-range 192.168.16.0/20;
}
interface so-0/1/1.0;
}
Copyright © 2001, Juniper Networks, Inc.
Area-Range Restrict
 Adding the restrict keyword to the area-range
command stops all routes in the range from entering
the backbone
 No Type 3 LSA will be injected into the backbone
 Configured on the ABR only
[edit protocols ospf]
user@host# set area 1 nssa area-range 192.168.16/20 restrict
[edit protocols ospf]
user@host# show
area 0.0.0.1 {
nssa {
default-lsa default-metric 10;
area-range 192.168.16.0/20 restrict;
}
interface so-0/1/1.0;
}
Copyright © 2001, Juniper Networks, Inc.
Review Questions
 What is the difference between area-range in NSSA
and a stub area?
Copyright © 2001, Juniper Networks, Inc.