Chapter 11: OSPF Configuration Guide

Default Cost of an OSPF Interface

The default cost of an OSPF interface is calculated using its bandwidth. A VLAN that is attached to an interface could have several ports of differing speeds. The bandwidth of an interface is represented by the highest bandwidth port that is part of the associated VLAN. The cost of an OSPF interface is inversely proportional to this bandwidth. The cost is calculated using the following formula:

Cost = 2000000000 / speed (in bps)

The following is a table of the port types and the OSPF default cost associated with each type:

Table 7. OSPF Default Cost Per Port Type

Port Media Type

Speed

OSPF Default Cost

 

 

 

Ethernet 1000

1000 Mbps

2

 

 

 

Ethernet 10/100

100 Mbps

20

 

 

 

Ethernet 10/100

10 Mbps

200

 

 

 

WAN (T1)

1.5 Mbps

1333

 

 

 

WAN (T3)

45 Mbps

44

 

 

 

To configure OSPF interface parameters, enter one of the following commands in Configure mode:

Enable OSPF state on interface.

ospf set interface <name-or-IPaddr>all

 

state disableenable

 

 

Specify the cost of sending a packet

ospf set interface <name-or-IPaddr>all

on an OSPF interface.

cost <num>

 

 

Specify the priority for determining

ospf set interface <name-or-IPaddr>all

the designated router on an OSPF

priority <num>

interface.

 

 

 

Specify the interval between OSPF

ospf set interface <name-or-IPaddr>all

hello packets on an OSPF interface.

hello-interval <num>

 

 

Configure the retransmission interval

ospf set interface <name-or-IPaddr>all

between link state advertisements for

retransmit-interval <num>

adjacencies belonging to an OSPF

 

interface.

 

 

 

114

SmartSwitch Router User Reference Manual

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Cabletron Systems 9032578-05 manual Default Cost of an Ospf Interface, Ospf Default Cost Per Port Type