Specifications

Send document comments to [e-mail].
3-4
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
All other routers establish adjacency with the DR and the BDR and use the IPv4 multicast address
224.0.0.6 to send LSA updates to the DR and BDR. Figure 3-1 shows this adjacency relationship
between all routers and the DR.
DRs are based on a router interface. A router might be the DR for one network and not for another
network on a different interface.
Figure 3-1 DR in Multi-Access Network
Areas
You can limit the CPU and memory requirements that OSPFv2 puts on the routers by dividing an
OSPFv2 network into areas. An area is a logical division of routers and links within an OSPFv2 domain
that creates separate subdomains. LSA flooding is contained within an area, and the link-state database
is limited to links within the area. You can assign an area ID to the interfaces within the defined area.
The Area ID is a 32-bit value that you can enter as a number or in dotted decimal notation, such as
10.2.3.1.
Cisco NX-OS always displays the area in dotted decimal notation.
If you define more than one area in an OSPFv2 network, you must also define the backbone area, which
has the reserved area ID of 0. If you have more than one area, then one or more routers become area
border routers (ABRs). An ABR connects to both the backbone area and at least one other defined area
(see Figure 3-2).
Router A Router B Router C
Router ERouter D
or DR
= Multi-access network
= Logical connectivity to Designated Router for OSPF
182982