Specifications

Send document comments to [e-mail].
3-6
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 3 Configuring OSPFv2
Information About OSPFv2
Link Cost
Each OSPFv2 interface is assigned a link cost. The cost is an arbitrary number. By default, Cisco NX-OS
assigns a cost that is the configured reference bandwidth divided by the interface bandwidth. By default,
the reference bandwidth is 40 Gb/s. The link cost is carried in the LSA updates for each link.
Flooding and LSA Group Pacing
When an OSPFv2 router receives an LSA, it forwards that LSA out every OSPF-enabled interface,
flooding the OSPFv2 area with this information. This LSA flooding guarantees that all routers in the
network have identical routing information. LSA flooding depends on the OSPFv2 area configuration
(see the “Areas” section on page 3-4). The LSAs are flooded based on the link-state refresh time (every
30 minutes by default). Each LSA has its own link-state 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 OSPFv2 to pack multiple LSAs into an OSPFv2 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
OSPFv2 load on your network.
Table 3-1 LSA Types
Type Name Description
1 Router LSA LSA sent by every router. This LSA includes the state and the cost of all
links and a list of all OSPFv2 neighbors on the link. Router LSAs trigger an
SPF recalculation. Router LSAs are flooded to local OSPFv2 area.
2 Network LSA LSA sent by the DR. This LSA lists all routers in the multi-access network.
Network LSAs trigger an SPF recalculation. See the “Designated Routers”
section on page 3-3.
3Network
Summary LSA
LSA sent by the area border router to an external area for each destination
in the local area. This LSA includes the link cost from the area border router
to the local destination. See the “Areas” section on page 3-4.
4 ASBR Summary
LSA
LSA sent by the area border router to an external area. This LSA advertises
the link cost to the ASBR only. See the “Areas” section on page 3-4.
5AS External
LSA
LSA generated by the ASBR. This LSA includes the link cost to an external
autonomous system destination. AS External LSAs are flooded throughout
the autonomous system. See the “Areas” section on page 3-4.
7 NSSA External
LSA
LSA generated by the ASBR within a not-so-stubby area (NSSA). This LSA
includes the link cost to an external autonomous system destination. NSSA
External LSAs are flooded only within the local NSSA. See the “Areas”
section on page 3-4.
9–11 Opaque LSAs LSA used to extend OSPF. See the “Opaque LSAs” section on page 3-7.