Specifications

Send document comments to [e-mail].
3-2
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
OSPFv2 supports IPv4.
This section includes the following topics:
• Hello Packet, page 3-2
• Neighbors, page 3-2
• Adjacency, page 3-3
• Designated Routers, page 3-3
• Areas, page 3-4
• Link-State Advertisements, page 3-5
• OSPFv2 and the Unicast RIB, page 3-7
• Authentication, page 3-7
• Advanced Features, page 3-8
Hello Packet
OSPFv2 routers periodically send Hello packets on every OSPF-enabled interface. The hello interval
determines how frequently the router sends these Hello packets and is configured per interface. OSPFv2
uses Hello packets for the following tasks:
• Neighbor discovery
• Keepalives
• Designated router election (see the “Designated Routers” section on page 3-3)
The Hello packet contains information about the originating OSPFv2 interface and router, including the
assigned OSPFv2 cost of the link, the hello interval, and optional capabilities of the originating router.
An OSPFv2 interface that receives these Hello packets determines if the settings are compatible with the
receiving interface settings. Compatible interfaces are considered neighbors and are added to the
neighbor table (see the “Neighbors” section on page 3-2).
Hello packets also include a list of router IDs for the routers that the originating interface has
communicated with. If the receiving interface sees its own router ID in this list, then bidirectional
communication has been established between the two interfaces.
OSPFv2 uses Hello packets as a keepalive message to determine if a neighbor is still communicating. If
a router does not receive a Hello packet by the configured dead interval (usually a multiple of the hello
interval), then the neighbor is removed from the local neighbor table.
Neighbors
An OSPFv2 interface must have a compatible configuration with a remote interface before the two can
be considered neighbors. The two OSPFv2 interfaces must match the following criteria:
• Hello interval
• Dead interval
• Area ID (see the “Areas” section on page 3-4)
• Authentication
• Optional capabilities