[c-nsp] ospf auto-cost reference-bandwidth on modern gigabit networks

[Mark Tinka]

On 29/Apr/20 17:04, Mike wrote:

> Hello,
>
>      Is there a recommended 'modern default' for ip ospf auto-cost
> reference-bandwidth, to account for the fact that modern networks have
> 1g and faster interfaces?
>
>     My core equipment all has 10G and 1G interfaces today, and it seems
> to me that if I set the reference-bandwidth to 100gbps, Im not losing
> anything, but gaining a useful distinction between the modern
> 1g,10g,40g,and 100g interfaces of today. I understand the necessity of
> setting this on all routers in the network, however, I do have some
> older equipment (cisco 7201) doing T1 aggregation that also has 1g
> interfaces with nothing higher, so I am wondering the practicality of
> maybe just skipping this default change on that and like gear? These
> devices are at the edge and further only have single uplink connections
> to the core so it would seem safe to not worry about this here.

When we moved to IS-IS in 2007, we decided to set our reference
bandwidth to 1Tbps (not in the routers, but as a concept).

My recommendation would be not to set the reference in the network.
Rather, have it as an architecture concept and deliberately design
metrics off of your reference. 1Tbps seemed reasonable in 2007. Who
knows, maybe 10Tbps is reasonable in 2020 (with the downside being that
your metrics will be very high for very slow links).

Mark.