Stan,
It's not a problem at all to construct routes where hop count is not the
best metric.
Was this at issue? Where did I say hop count was always best?
Or were you trying to suggest that bandwidth, as a non-cost metric, was
sometimes useful? Well, yes, of course it is.
There are well-known cost metrics that enable comparisons of routes to
select the one with the best bandwidth. I have mentioned them before in
conversations on this list about this subject.
If my part of the discussion is simply to be dismissed as protestations,
I wish someone would just tell me. I'd much prefer to know how to
participate in a constructive discussion.
Regards,
Charlie P.
On 9/27/2015 2:52 PM, Stan Ratliff wrote:
On Sun, Sep 27, 2015 at 5:31 PM, John Dowdell <john.dowdell486@xxxxxxxxx <mailto:john.dowdell486@xxxxxxxxx>> wrote:
Charlie
> On 24 Sep 2015, at 21:48, Charlie Perkins
<charles.perkins@xxxxxxxxxxxxx
<mailto:charles.perkins@xxxxxxxxxxxxx>> wrote:
>
> Hello John,
>
> Follow-up below...
>
>
> Bandwidth is not a cost metric. The calculation of LoopFree()
might be more complicated. I don't like non-cost metrics for
various reasons. One reason is that they contradict the entire
mathematical formulation for metrics and metric spaces. On the
other hand, some people in the IETF don't have much respect for
mathematics, it seems, and I get tired of complaining about it.
>
> Regards,
> Charlie P.
>
Bandwidth is a metric (along with latency, both of which are
declared as metrics in DLEP). You can use it to influence routing
decisions, but I’ll agree that it doesn’t work to completely drive
a route selection in the way that hop count does.
So, let me construct a network scenario where I have two paths to a device:
Source------Router1--------Router2---------Router3-------Router4-------Destination
But, all of the dashed lines in the above description depict 10Gb/sec copper.
Second path:
Source-----Router1-------------------Router3-------Router4------Destination
But the long dashed line between Router1 and Router3 is a satellite backup link, at 1Mb/sec. I understand - it's a hypothetical case. But stuff like this pops up all the time in real networks.
First route, hop count 5. Second route, hop count 4. Based on Charlie's protestations, I should assume the second route is better than the first? FWIW, I don't. If there's any way on earth I can take the first route, I will.
Stan
I believe it is also impossible to calculate LoopFree() just using
bandwidth, so maybe you’d have to use a combination of hop count
and bandwidth, but that is a discussion for another draft.
Regards
John
