[50148] in North American Network Operators' Group
RE: IGP metrics on WAN links
daemon@ATHENA.MIT.EDU (Frank Scalzo)
Fri Jul 19 16:53:46 2002
Date: Fri, 19 Jul 2002 16:51:27 -0400
From: "Frank Scalzo" <frank.scalzo@amerinex.net>
To: "Daniel Golding" <dgolding@sockeye.com>,
"Joe Abley" <jabley@automagic.org>, "Me" <smentzer@mentzer.org>
Cc: "Sush Bhattarai" <netnews@sush.org>, <nanog@merit.edu>,
"Tom Holbrook" <tomhol@corp.earthlink.net>
Errors-To: owner-nanog-outgoing@merit.edu
MPLS allows you to do the best of both worlds. You can set your TE =
metrics to the latency/route-miles and then build bandwidth constrained =
LSPs from place to place and they will take the least latent, =
uncongested path that they fit on.=20
Similar things can be done with ATM routing costs, and contracts on =
spvcs.=20
Both of these are considerably more work, but it gets traffic flows on =
good paths very well.
There is at least one large ISP doing metrics in that manner.
-----Original Message-----
From: Daniel Golding [mailto:dgolding@sockeye.com]
Sent: Fri 7/19/2002 4:43 PM
To: Joe Abley; Me
Cc: Sush Bhattarai; nanog@merit.edu; Tom Holbrook
Subject: RE: IGP metrics on WAN links
I suspect the approach you take depends on how your network looks. If =
you
have many pipes of a variety of sizes, doing IGP metrics based on pipe =
size
makes a good deal of sense, then adding twists for things like ckt =
latency.
However, folks with uniform sized networks, and uniform traffic between
coasts probably tend to set IGP metrics for latency, with pipe size =
being
the exception that they bias for afterwards.
The latter is probably more prevelent in an established network, the =
former
in a network undergoing a large fiber build.
- Dan
> -----Original Message-----
> From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of
> Joe Abley
> Sent: Friday, July 19, 2002 4:25 PM
> To: Me
> Cc: Sush Bhattarai; nanog@merit.edu; Tom Holbrook
> Subject: Re: IGP metrics on WAN links
>
>
>
> 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
>
