ZyXEL Communications XGS-4728F - Manual (Page 275)

Chapter 32 OSPF
XGS-4728F User’s Guide
275
When you configure an OSPF interface, you first set an interface to transmit OSPF
traffic and add the interface to an area.
You can configure a virtual link to establish/maintain connectivity between a non-
backbone area and the backbone. The virtual link must be configured on both
layer 3 devices in the non-backbone area and the backbone.
32.1.4 OSPF and Router Elections
The OSPF protocol provides for automatic election of Designated Router (DR) and
Backup Designated Router (BDR) on network segments. The DR and BDR keep
track of link state updates in their area and make sure LSAs are sent to the rest of
the network.
In most cases the default DR/BDR election is fine, but in some situations it must
be controlled. In the following figure only router A has direct connectivity with all
the other routers on the network segment. Routers B and C do not have a direct
connection with each other. Therefore they should not be allowed to become DR or
BDR. Only router A should become the DR.
Figure 147 OSPF Router Election Example
You can assign a priority to an interface which determines whether this router will
be elected to be a DR or BDR. The router with the highest priority becomes the
DR, while a router with a priority of 0 does not participate in router elections. In
Figure 147 on page 275 you can assign a priority of 0 to routers B and C, thereby
ensuring they do not become DR or BDR and assign a priority of 1 to router A to
make sure that it does become the DR.
32.1.5 Configuring OSPF
To configure OSPF on the Switch , do the following tasks
1
Enable OSPF
2
Create OSPF areas