3Com 7700 Configuration Manual page 90

82 C 5: R P
HAPTER OUTING
O
ROTOCOL PERATION
Perform the following configuration in VLAN interface view.
Table 26 Configure 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.
Configure 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.
Table 27 Configure 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
Set 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. Votes are the hello packets. 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 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 also exchanged between them. When the
DR fails, the BDR becomes the DR instantly. Since no re-election is needed and the
adjacencies have already been established, the process is very short. But in this
case, a new BDR must be elected. Although it also takes a long time, it does not
affect the route calculation.
Command
ospf network-type { broadcast | NBMA | P2MP | P2P }
Command
ospf cost value
undo ospf cost