[c-nsp] ospf cost

[Pete Templin]

Jon Lewis wrote:

> I think what I've run into is a limitation in the default ospf cost
> calculation which causes any interface with BW >= 100mbit to end
> up with a cost of 1.  I see I can raise that with something like:
> 
> router ospf 1
>  auto-cost reference-bandwidth 10000
> 
> but that causes a warning telling me I better make sure all my routers
> have the same reference-bandwidth setting.  I assume that's so other
> routers don't end up with whacked out SP trees based on wildly different
> interface costs across the network.
> 
> If anyone's already changed this, was it the sort of thing you rolled out
> across the whole network as quickly as possible during a late night
> maintenance window?

I had the "joy" of a mixed Cisco/Riverstone network.  After a vicious 
network outage, we helped Riverstone realize that their documentation 
(in a total of five places) gave three different default values, and 
their ref-bw command didn't actually change the cost for WAN interfaces. 
  :)  We were having major issues at the time, so we rapidly changed to 
Riverstone's default of 2Gbps (I had rolled out all of the Cisco stuff, 
and supposedly the Riverstone stuff, with a ref-bw of 10Gbps).

I would guess you could look at your network, develop a "left-to-right" 
sequence, and roll it out in a night.  Alternatively, you could manually 
set each link to a new cost value, change the ref-bw, then optionally 
remove the manual cost values.

pt