OSPF - Part 4

OSPF Costs
Default costs
1.1785 on 56kbps serial link
2.64 on T1 (1.544Mbps serial link)
3.10 on Ethernet
4.1 on Fast Ethernet
5.1 on Gigabit Ethernet

Calculation
Cost = 100Mbps/bandwidth, where 100Mbps is default reference bandwidth

Command syntax:
router(config-if)# ip ospf cost value(0~65535)
OR
router(config-if)# ospf auto-cost reference-bandwidth value(1~4,294,967)

100Mbps သည္ default reference bandwidth ျဖစ္ကာ ၄င္းအားတိုးျမင့္ျခင္းျဖင့္ (eg. 1000Mbps) network performance ကို ျမင့္တင္နိုင္သည္။ ဥပမာ… default အားျဖင့္ Gigabit Ethernet cost ကို 1 (Fast Ethernet နွင့္တူသည္) ဟုထားေသာေၾကာင့္ ထိေရာက္ေသာ network performance ကိုမရရွိနုိင္ပါ… reference bandwidth ကိုတိုးျမင့္ျခင္းျဖင့္ ေျဖရွင္းရသည္။

Example: ref: http://ccietobe.blogspot.com/

R1#show ip route | begin Gateway
Gateway of last resort is not set
1.0.0.0 /32 is subnetted, 2 subnets
C 1.1.1.1 is directly connected, Loopback0
C 1.1.1.2 is directly connected, Loopback1
2.0.0.0 /32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 172.12.12.2, 00:08:50, Serial1/0
4.0.0.0 /32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/129] via 172.12.12.2, 00:08:50, Serial1/0
172.12.0.0 /24 is subnetted, 2 subnets
C 172.12.12.0 is directly connected, Serial1/0
O IA 172.12.23.0 [110/128] via 172.12.12.2, 00:08:50, Serial1/0

R1#show ip ospf int s1/0 | inc Cost
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64

Chaging the reference-bandwidth:

R1(config)#router ospf 1
R1(config-router)#auto-cost reference-bandwidth 1000
% OSPF: Reference bandwidth is changed.

R1#show ip ospf int s1/0 | inc Cost
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 647

Calculations:

100000000/1544000 = 64
1000000000/1544000 = 647

R1#show ip route | begin Gateway
Gateway of last resort is not set
1.0.0.0 /32 is subnetted, 2 subnets
C 1.1.1.1 is directly connected, Loopback0
C 1.1.1.2 is directly connected, Loopback1
2.0.0.0 /32 is subnetted, 1 subnets
O 2.2.2.2 [110/648] via 172.12.12.2, 00:01:30, Serial1/0
4.0.0.0 /32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/712] via 172.12.12.2, 00:01:30, Serial1/0
172.12.0.0 /24 is subnetted, 2 subnets
C 172.12.12.0 is directly connected, Serial1/0
O IA 172.12.23.0 [110/711] via 172.12.12.2, 00:01:30, Serial1/0

19/4/2011