Send document comments to nexus7k-docfeedback@cisco.com.
6-7
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 6 Configuring OSPFv2
Information About OSPFv2
Link-State Database
Each router maintains a link-state database for the OSPFv2 network. This database contains all the
collected LSAs, and includes information on all the routes through the network. OSPFv2 uses this
information to calculate the bast path to each destination and populates the routing table with these best
paths.
LSAs are removed from the link-state database if no LSA update has been received within a set interval,
called the MaxAge. Routers flood a repeat of the LSA every 30 minutes to prevent accurate link-state
information from being aged out. Cisco NX-OS supports the LSA grouping feature to prevent all LSAs
from refreshing at the same time. For more information, see the “Flooding and LSA Group Pacing”
section on page 6-6.
Opaque LSAs
Opaque LSAs allow you to extend OSPF functionality. Opaque LSAs consist of a standard LSA header
followed by application-specific information. This information might be used by OSPFv2 or by other
applications. OSPFv2 uses Opaque LSAs to support OSPFv2 Graceful Restart capability (see the “High
Availability and Graceful Restart” section on page 6-11). Three Opaque LSA types are defined as
follows:
• LSA type 9—Flooded to the local network.
• LSA type 10—Flooded to the local area.
• LSA type 11—Flooded to the local autonomous system.
OSPFv2 and the Unicast RIB
OSPFv2 runs the Dijkstra shortest path first algorithm on the link-state database. This algorithm selects
the best path to each destination based on the sum of all the link costs for each link in the path. The
resultant shortest path for each destination is then put in the OSPFv2 route table. When the OSPFv2
network is converged, this route table feeds into the unicast RIB. OSPFv2 communicates with the unicast
RIB to do the following:
• Add or remove routes
• Handle route redistribution from other protocols
• Provide convergence updates to remove stale OSPFv2 routes and for stub router advertisements (see
the “OSPFv2 Stub Router Advertisements” section on page 6-12)
OSPFv2 also runs a modified Dijkstra algorithm for fast recalculation for summary and external (type
3, 4, 5, and 7) LSA changes.
Authentication
You can configure authentication on OSPFv2 messages to prevent unauthorized or invalid routing
updates in your network. Cisco NX-OS supports two authentication methods:
• Simple password authentication
• MD5 authentication digest
You can configure the OSPFv2 authentication for an OSPFv2 area or per interface.
To Next Page
Loading...
