Designated Routers - Cisco Nexus 7000 Series Configuration Manual

Information About 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 .
updated. The local router sends a Link State Request packet for each LSA that it needs new or updated
information on. The neighbor responds with a Link State Update packet. This exchange continues until
both routers have the same link-state information.

Designated Routers

Networks with multiple routers present a unique situation for OSPFv3. If every router floods the network
with LSAs, the same link-state information will be sent from multiple sources. Depending on the type
of network, OSPFv3 might use a single router, the
represent the network to the rest of the OSPFv3 area (see the
fails, OSPFv3 selects a
Network types are as follows:
•
•
The DR and BDR are selected based on the information in the Hello packet. When an interface sends a
Hello packet, it sets the priority field and the DR and BDR field if it knows who the DR and BDR are.
The routers follow an election procedure based on which routers declare themselves in the DR and BDR
fields and the priority field in the Hello packet. As a final tie breaker, OSPFv3 chooses the highest router
IDs as the DR and BDR.
All other routers establish adjacency with the DR and the BDR and use the IPv6 multicast address
FF02::6 to send LSA updates to the DR and BDR.
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 7-1
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
7-4
backup designated router
Point-to-point—A network that exists only between two routers. All neighbors on a point-to-point
network establish adjacency and there is no DR.
Broadcast—A network with multiple routers that can communicate over a shared medium that
allows broadcast traffic, such as Ethernet. OSPFv3 routers establish a DR and BDR that controls
LSA flooding on the network. OSPFv3 uses the well-known IPv6 multicast addresses, FF02::5, and
a MAC address of 0100.5300.0005 to communicate with neighbors.
DR in Multi-Access Network
Router A
Router D
or DR
= Multi-access network
= Logical connectivity to Designated Router for OSPF
designated router (DR), to control the LSA floods and
"Areas" section on page
(BDR). If the DR fails, OSPFv3 uses the BDR.
Figure 7-1 shows this adjacency relationship between
Router B
Router E
Chapter 7 Configuring OSPFv3
7-5). If the DR
Router C
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