Route Redistribution; Route Summarization - Cisco Nexus 7000 Series Configuration Manual

Information About OSPFv2
S e n d d o c u m e n t c o m m e n t s t o n e x u s 7 k - d o c f e e d b a c k @ c i s c o . c o m .
Figure 6-4
Area 0
Area 5
You can also use virtual links to temporarily recover from a partitioned area, which occurs when a link
within the area fails, isolating part of the area from reaching the designated ABR to the backbone area.

Route Redistribution

OSPFv2 can learn routes from other routing protocols by using route redistribution. See the
Redistribution" section on page
routes or a default link cost for all redistributed routes.
Route redistribution uses route maps to control which external routes are redistributed. You must
configure a route map with the redistribution to control which routes are passed into OSPFv2. A route
map allows you to filter routes based on attributes such as the destination, origination protocol, route
type, route tag, and so on. You can use route maps to modify parameters in the AS External (type 5) and
NSSA External (type 7) LSAs before these external routes are advertised in the local OSPFv2
autonomous system. See
route maps.

Route Summarization

Because OSPFv2 shares all learned routes with every OSPF-enabled router, you might want to use route
summarization to reduce the number of unique routes that are flooded to every OSPF-enabled router.
Route summarization simplifies route tables by replacing more-specific addresses with an address that
represents all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and
10.1.3.0/24 with one summary address, 10.1.0.0/16.
Typically, you would summarize at the boundaries of area border routers (ABRs). Although you could
configure summarization between any two areas, it is better to summarize in the direction of the
backbone so that the backbone receives all the aggregate addresses and injects them, already
summarized, into other areas. The two types of summarization are as follows:
•
•
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
6-10
Virtual Links
ABR2
Chapter 16, "Configuring Route Policy Manager,"
Inter-area route summarization
External route summarization
ABR1
1-6. You configure OSPFv2 to assign a link cost for these redistributed
Chapter 6 Configuring OSPFv2
Area 3
"Route
for details on configuring
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