Configuring OSPF Routing
Introduction to OSPF
MultiVoice Gateway for the MAX— User’s Guide
Preliminary November 23, 1998
9-7
In a stub area, routing to AS-external destinations is based on a per-area default cost. The
per-area default cost is advertised to all routers within the stub area by a border router, and is
used for all external destinations.
If the MultiVoice Gateway supports external routes across its WAN links, you should not
configure it in a stub area. Because an ABR configuration is not currently recommended for
the MultiVoice Gateway, the area in which it resides should not be a stub area if any of its links
are AS-external.
Not So Stubby Areas (NSSAs)
The MultiVoice Gateway supports OSPF Not So Stubby Areas (NSSAs) as described in RRC
1587. NSSAs allow you to treat complex networks similarly to stub areas. This can simplify
your network’s topology and reduce OSPF-related traffic.
NSSAs and Type-7 LSAs
NSSAs are similar to stub areas, except that they allow limited importing of Autonomous
System (AS) external routes. NSSAs use Type-7 LSAs to import external route information
into an NSSA. Type-7 LSAs are similar to Type-5 LSAs except that:
•
NSSAs can originate and import Type-7 LSAs. Like stub areas, NSSAs cannot originate
or import Type-5 LSAs.
•
Type-7 LSAs can only be advertised within a single NSSA. They are not flooded
throughout the AS as are Type-5 LSAs.
When you configure the MultiVoice Gateway as an NSSA internal router, you define the
Type-7 LSAs you want to advertise throughout the NSSA as static routes.
You must also specify whether these Type-7 LSAs should be advertised outside the NSSA. If
you choose to advertise a Type-7 LSA, the NSSA Area Border Router (ABR) converts it to a
Type-5 LSA, which can then be flooded throughout the AS. If you choose not to advertise a
Type-7 LSA, it is not advertised beyond the NSSA.
(For complete information on NSSAs, see RFC 1587.)
Configuring the MultiVoice Gateway as an NSSA internal router
Because the MultiVoice Gateway cannot be an area border router, when you configure OSPF
on the MultiVoice Gateway keep in mind that:
•
The Area-Type must be the same on all MultiVoice Gateway interfaces running OSPF.
•
The Area ID (configured in the Area parameter) must be the same on all MultiVoice
Gateway interfaces running OSPF.
To configure the MultiVoice Gateway as an NSSA:
1
Select Ethernet > Mod Config > OSPF options.
2
Set AreaType to NSSA.
3
Exit and save the Mod Config profile.
4
Select Ethernet > Static Rtes > any Static Route profile.
5
Configure a static route to the destination outside the NSSA.
