Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Designated Router
Depending on the type of network, OSPFv3 might use a single router, the Designated Router (DR), to control the LSA floods
and represent the network to the rest of the OSPFv3 area.
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.
Backup Designated Router
If the DR fails, OSPFv3 will promote the Backup Designated Router (BDR) to DR.
Network Types
Network types are as follows:
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 33:33:00:00:00:05 to communicate with
neighbors.
Router Selection
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 can identify the DR and BDR.
To accomplish this, the routers follow an election procedure based on which the routers declare themselves in the
following:
The DR and BDR fields
The priority field of the Hello packet.
As a final alternative, OSPFv3 chooses the highest router IDs as the DR and BDR.
