OSPF Costs Formula that include delay.

Fri Jan 24 20:36:48 UTC 2014

Some networks I have worked with took the average latency of each link and assigned that (with some constant multiple) as the interface cost.

Of course this all fails miserably if you are using anything like MPLS underneath your OSPF.

Owen

On Jan 24, 2014, at 12:26 PM, Erik Sundberg <ESundberg at nitelusa.com> wrote:

> I understand OSPF default calculation for cost doesn't include delay. I am looking for a formula that I can use to manually set the OSPF costs that factors in delay.
> 
> When using OSPF's default costs, the shortest path is not always the optimal path.
> 
> 
> Example
> 
> New York to Los Angeles. Assuming all links are the same bandwidth and have a ospf cost of 1.
> 
> Path 1 (75ms) - OSPF Cost 2 - New York > Dallas > Los Angeles
> 
> Path 2 (65ms) - OSPF Cost 3 - New York > Chicago > Denver > Los Angeles
> 
> If I left the default cost's alone then path 1 would win because it has a lower ospf cost, however it take traffic 10ms longer to get there.
> 
> However I would like traffic to take Path 2 by adjusting the OSPF cost.
> 
> 
> I am looking for a formula that other people are using .p
> 
> Thanks
> 
> Erik
> 
> 
> -----Original Message-----
> From: Randy [mailto:randy_94108 at yahoo.com]
> Sent: Thursday, January 23, 2014 9:03 PM
> To: Erik Sundberg; nanog at nanog.org
> Subject: Re: OSPF Costs Formula that include delay.
> 
> 
> 
> ----- Original Message -----
>> From: Erik Sundberg <ESundberg at nitelusa.com>
>> To: "nanog at nanog.org" <nanog at nanog.org>
>> Cc:
>> Sent: Thursday, January 23, 2014 4:47 PM
>> Subject: OSPF Costs Formula that include delay.
>> 
>> What is everyone using for an OSPF cost formula that factors in a
>> circuits delay and bandwidth (10M-100G)???
>> 
>> Thanks in advance
> 
> 
> 
> umm..are you sure your question is not about EIGRP?
> OSPF has no concept of interface-delays.
> 
> The default reference bandwidth for OSPF is 100M
> 
> In your case if you set your reference bandwidth to 100000 your 100G links would have a link cost of 1, 10G - 10, 1G-100, 100M-1000 and 10M-10000
> 
> A vendor specific list would be a better place to ask.
> 
> 
> ./Randy
> 
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