From: Harish DV/peakxv (harish.dv@xxxxxxxxxx)
Date: Wed Jul 17 2002 - 22:06:12 GMT-3
To add to this..
the "ip ospf cost" interface command will override this.
Harish
"Brian McGahan"
<brian@cyscoexper To: "'Shuyi Li'" <shuli@ci
sco.com>, "'Jason Sinclair'"
t.com> <sinclairj@powertel.com.au>
Sent by: cc: "'Tom Young'" <gitsyou
ng@yahoo.co.jp>, <ccielab@groupstudy.com>
nobody@groupstudy Subject: RE: OSPF 's cost and m
etric
.com
07/17/2002 03:54
PM
Please respond to
"Brian McGahan"
Shuyi,
The "bandwidth" value of a link doesn't have anything to do
with
the physical bandwidth of the interface. For example, a serial
interface on a 2500 series router has a bandwidth *value* of 1544 Kbps.
This does not reflect that these interfaces can physically support up to
2Mbps or 4Mbps, and whether or not you have a 256Kbps frame-relay
circuit attached to it. The "bandwidth" value of an interface is
static, and is set using the interface "bandwidth" command.
OSPF computes it's cost value by taking (ReferenceBandwidth /
InterfaceBandwith) ReferenceBandwidth has a default value of 10^8 bps,
or 100Mbps. Therefore a 100Mbps FastEthernet interface has a cost of 1.
The reference bandwidth value can be changed with the OSPF command "
auto-cost reference-bandwidth X" where X is the reference bandwidth in
terms of Mbits per second. If you want a Gigabit link to have a cost of
1, the reference bandwidth should be 1000.
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
http://www.cyscoexpert.com
Voice: 847.674.3392
Fax: 847.674.2625
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Shuyi Li
Sent: Wednesday, July 17, 2002 1:20 PM
To: Jason Sinclair
Cc: 'Tom Young'; ccielab@groupstudy.com
Subject: RE: OSPF 's cost and metric
Jason,
Regarding the OSPF metric, I have a question for you that, the cost of
links is considered to be the current available BW, or just the total BW
even it's being occupied, say 50%. Please advise.
thanks in advance.
/shuyi
At 05:22 PM 7/17/2002 +1000, Jason Sinclair wrote:
>Tom,
>
>In OSPF the metric is the cost. What I mean here is best clarified as
>follows:
>
>1. In RIP the metric as we know is hop count.
>2. EIGRP/IGRP use a composite metric based on things such as bandwidth,
>delay, etc
>3. In OSPF the metric is based on the cost of links. The lower the cost
the
>more preferred the path
>
>Hope this makes sense.
>
>Regards,
>
>Jason Sinclair CCIE #9100
>Manager, Network Control Centre
>POWERTEL
>55 Clarence Street,
>SYDNEY NSW 2000
>AUSTRALIA
>office: + 61 2 8264 3820
>mobile: + 61 416 105 858
>email: sinclairj@powertel.com.au
>
>-----Original Message-----
>From: Tom Young [mailto:gitsyoung@yahoo.co.jp]
>Sent: Wednesday, 17 July 2002 16:35
>To: ccielab@groupstudy.com
>Subject: OSPF 's cost and metric
>
>Hi, group.
>
> The OSPF's "cost" and "metric" parameters made me
>confused. Who can clear it for me?
>
>
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