3Com SuperStack 4 Configuration Manual page 124

136 C 6: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
Perform the following configuration in Interface View:
Table 135 Configuring a Network Type on the Interface That Starts OSPF
Operation
Configure network
type on the interface
After the interface has been configured with a new network type, the original
network type of the interface is removed automatically.
Configuring the Cost for Sending Packets on an Interface
You can control 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 Interface View:
Table 136 Configuring the cost for sending packets on the Interface
Operation
Configure the cost for sending packets on Interface
Restore the default cost for packet transmission on the Interface
For the Switch 5500G-EI the default cost for running OSPF protocol on the VLAN
interface is 10.
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 will be 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 the priorities greater than 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 will be elected as the 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 higher priority is elected DR. If the priorities are the same, the router with
the higher router ID is elected DR. If the priority of a router is 0, it will not be
elected as DR or BDR.
If 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 be incorrect. To speed up this DR replacement process, OSPF
implements the BDR as 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
fails, the BDR becomes the DR. Since no re-election is needed and the adjacencies
have already been established, the process is very quick. But in this case, a new
BDR should be elected. Although it also takes a long time, it does not influence
route calculation.
Command
ospf network-type { broadcast | nbma | p2mp | p2p }
Command
value
ospf cost
undo ospf cost