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OSPF 87
the network type to P2MP manually. The most common method is to change a
partially connected NBMA network to a P2MP network.
■ NBMA forwards packets by unicast and requires neighbors to be configured
manually. P2MP forward packets by multicast.
Perform the following configuration in VLAN interface view.
After the interface has been configured with a new network type, the original
network type is removed automatically.
Configuring the Cost for Sending Packets on an Interface
The user can control the network traffic by configuring different message sending
costs for different interfaces. Otherwise, OSPF automatically calculates the cost
according to the baud rate on the current interface.
Perform the following configuration in VLAN interface view.
Setting the Interface Priority for DR Election
The priority of the router interface determines the qualification of the interface for
DR election. A router of higher priority is considered first if there is a collision in the
election.
DR is not designated manually, instead, it is elected by all the routers on the
segment. Routers with priorities > 0 in the network are eligible candidates. Among
all the routers self-declared to be the DR, the one with the highest priority is
elected. If two routers have the same priority, the one with the highest router ID is
elected DR. Each router writes the expected DR in the packet and sends it to all the
other routers on the segment. If two routers attached to the same segment
concurrently declare themselves to be the DR, the one with the higher priority
wins. If the priorities are the same, the router with higher router ID wins. If the
priority of a router is 0, it is not eligible to be elected DR or BDR.
If a DR fails, the routers on the network must elect a new DR and synchronize with
the new DR. The process takes a relatively long time, during which, route
calculation can become incorrect. To speed up this DR replacement process, OSPF
implements the BDR as a backup for DR. The DR and BDR are elected at the same
time. The adjacencies are also established between the BDR and all the routers on
the segment, and routing information is exchanged between them. When the DR
Table 27 Configuring a Network Type on the Interface that Starts OSPF
Operation Command
Configure network type on the interface ospf network-type { broadcast | NBMA |
P2MP | P2P }
Restore the default network type of the OSPF
interface
undo ospf network-type
Table 28 Configuring the Cost for Sending Packets on the Interface
Operation Command
Configure the cost for sending packets on
interface
ospf cost value
Restore the default cost for packet
transmission on the interface
undo ospf cost