From: Brian McGahan (brian@cyscoexpert.com)
Date: Sat Apr 12 2003 - 12:56:36 GMT-3
Peter,
cost = reference_bandwidth / bandwidth
By default, reference_bandwidth is 100Mbps. Therefore a Fast Ethernet
(or FDDI) link is a cost of 1.
If you want a 1Gbps link to have a cost of 1, we must solve for
reference_bandwidth
1 = reference_bandwidth / 1000Mbps
1000 * (1) = (reference_bandwidth / 1000) * 1000
1000 = reference_bandwidth
Similarly, if you want a 1Gbps link to have a cost of 5:
5 = reference_bandwidth / 1000Mbps
5000 = reference_bandwidth
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866-CyscoXP
Outside US: 847.674.3392
Fax: 847.674.2625
-----Original Message-----
From: Kash [mailto:kash2331@yahoo.com]
Sent: Saturday, April 12, 2003 8:03 AM
To: pita40; ccielab@groupstudy.com
Cc: Brian McGahan
Subject: Re: auto-cost reference-bandwidth
Hi,
Well as u might know that OSPF calculates the BW in a way that it is
100,000,000/(BW of interface). so for a Gig link it would be
(100,000,000/(1000,000,000)) which comes out to be .1 and is taken as 1.
This makes the Fast ethernet (100,000,000/(100,000,000))=1 also look the
same to OSPF. Ethernet is 10.
To change that u use the command
auto-cost reference-bandwidth nnnnn (where nnnn value will be in Mbits)
for eg to make Gigabit look better than Fast ethernet u would use the
command
auto-cost reference-bandwidth 1000
This would make Gig -1 Fast Ether -10 and Ethernet -100
So based on this u would use the command
auto-cost reference-bandwidth 5000
This would make Gig - 5 Fast Ether - 10 and Ethernet -500
Hope this helps u out.
Kashif
pita40 <pita40@hotmail.com> wrote:
I am confused with this command, according to cco
The following example changes the cost of the FDDI link to 10, while the
gigabit Ethernet link remains at a cost of 1. Thus, the link costs are
differentiated.
router ospf 1
auto-cost reference-bandwidth 1000
How does the router no only to reference the FDDI link?
Also, how do I make the gig link have a cost of 5 ?
Help.
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