3Com Switch 8800 Configuration Guide
Chapter 19 OSPF Configuration
19-5
Since all the areas should be connected to the backbone area, virtual link is adopted so
that the physically separated areas can still maintain the logic connectivity to the
backbone area.
V. Route summary
An AS is divided into different areas that are interconnected via OSPF ABRs. The
routing information between areas can be reduced through route summary. Thus, the
size of routing table can be reduced and the calculation speed of the router can be
improved. After calculating an intra-area route of an area, the ABR summarizes
multiple OSPF routes into an LSA and sends it outside the area according to the
configuration of summary.
For example, as shown in Figure 19-1, the Area 19 has three area intra-area routes:
19.1.1.0/24, 19.1.2.0/24 and 19.1.3.0/24. The three routes are summarized into one
route 19.1.0.0/16 after you configured route summary. The RTA only generates an LSA,
describing the summarized route.
Area 12
Area 8
Area 19
Area 0
Virtual Link
19.1.1.0/24
19.1.2.0/24
19.1.3.0/24
RTA
Figure 19-1
Area and route aggregation
19.1.6 OSPF Features Supported by the Switch 8800
The Switch 8800 supports the following OSPF features:
z
Support stub areas: OSPF defines stub areas to decrease the overhead when the
routers within the area receive ASE routes.
z
Support NSSA: OSPF defines NSSA areas, surmounting the restriction of stub
areas on topology. NSSA is the abbreviation of Not-So-Stubby Area.
z
Support OSPF Multi-Process: A router runs multiple OSPF processes.
z
Share the discovered routing information with other dynamic routing protocols:
OSPF currently can import static routes and routes of other dynamic routing
protocols such as RIP into the autonomous system of the router, or advertise the
routing information discovered by OSPF to other routing protocols.
