Re: IGP metrics on WAN links

[Joe Abley <jabley () automagic org>]

On Fri, Jul 19, 2002 at 02:11:29PM -0600, Me wrote:
> I think you missed part of his comment:
> " of course there are always some "twinking" done regularly to give higher
> priorities to the higher bandwidth, link condition etc"
>
> so fiber mileage is just the base, with modifications to make it work
> correctly, based on bandwidth, etc.

Yeah, my (limited) experience is the opposite. At the previous large
operator at which I had enable, the IGP metrics were chosen primarily
according to circuit size, and were subsequently tweaked for other
issues (such as circuit latency, or the requirement to balance cross-
US traffic across non-parallel circuits).

In my experience, congestion is a much more effecive killer of service
than latency due to optical distance. Hence attracting traffic to
circuits where there is more likely to be headroom seems a more
reasonable first-order approach for choosing metrics.

That experience is all in networks where intra-AS traffic engineering
was done at the IP layer, however; in networks where there is a lower
layer of soft traffic engineering maybe other approaches would be more
appropriate.


Joe