Flooding And Lsa Group Pacing; Link-State Database - Cisco Nexus 7000 Series Configuration Manual

Chapter 7 Configuring OSPFv3
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 .

Flooding and LSA Group Pacing

OSPFv3 floods LSA updates to different sections of the network, depending on the LSA type. OSPFv3
uses the following flooding scopes:
•
•
•
LSA flooding guarantees that all routers in the network have identical routing information. LSA flooding
depends on the OSPFv3 area configuration (see the
based on the
refresh time.
You can control the flooding rate of LSA updates in your network by using the LSA group pacing
feature. LSA group pacing can reduce high CPU or buffer utilization. This feature groups LSAs with
similar link-state refresh times to allow OSPFv3 to pack multiple LSAs into an OSPFv3 Update
message.
By default, LSAs with link-state refresh times within four minutes of each other are grouped together.
You should lower this value for large link-state databases or raise it for smaller databases to optimize the
OSPFv3 load on your network.

Link-State Database

Each router maintains a link-state database for the OSPFv3 network. This database contains all the
collected LSAs, and includes information on all the routes through the network. OSPFv3 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
section on page
Multi-Area Adjacency
OSPFv3 multi-area adjacency allows you to configure a link on the primary interface that is in more than
one area. This link becomes the preferred intra-area link in those areas. Multi-area adjacency establishes
a point-to-point unnumbered link in an OSPFv3 area that provides a topological path for that area. The
primary adjacency uses the link to advertise an unnumbered point-to-point link in the RouterLSA for the
corresponding area when the neighbor state is full.
The multi-area interface exists as a logical construct over an existing primary interface for OSPF;
however, the neighbor state on the primary interface is independent of the multi-area interface. The
multi-area interface establishes a neighbor relationship with the corresponding multi-area interface on
the neighboring router. See the
information.
OL-20002-02
Link-local—LSA is flooded only on the local link, and no further. Used for Link LSAs and Grace
LSAs.
Area-local—LSA is flooded throughout a single OSPF area only. Used for Router LSAs, Network
LSAs, Inter-Area-Prefix LSAs, Inter-Area-Router LSAs, and Intra-Area-Prefix LSAs.
AS scope—LSA is flooded throughout the routing domain. Used for AS External LSAs.
link-state refresh
7-7.
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
"Areas" section on page
time (every 30 minutes by default). Each LSA has its own link-state
"Configuring Multi-Area Adjacency" section on page 7-25
Information About OSPFv3
7-5). The LSAs are flooded
"Flooding and LSA Group Pacing"
for more
7-7