On Thu, 30 Apr 2020 at 12:31, Robert Raszuk <rob...@raszuk.net> wrote:
> It is like GPS putting all cars on the big and congested highway when you > have a totally empty asphalt side road next to it :) > > The BW based IGP metric mapping comes from times of F/R, 64 kbps satellite > uplinks and zyxel DTE/DCE V.35 devices. I'm skeptical SPT topology ever was remotely typical where it made sense. It may work approximately, but that's not because it's good SPT, that's because acceptable outcome has large overlap with possible implementations. Two examples spring to mind 1) 10GE network, where you have 1G tails redundantly connected, you don't want the 1G tail to transit any of the 10GE traffic. You actually want overload or similar, the dual-connected 1GE is never desirable to transit. 2) 10GE core, with 1G islands attached to it, 1G will transit 1G inside 1G island, but you don't want 1G island to transit 10GE core. So you actually want a penalty on the island-border, so traffic doesn't cross it. (i.e. role based). In both above cases, people want distance-vector, with constraints, and BW based may approximate correct behaviour, but correct behaviour is actually very different from BW SPT. I think an interesting exercise is, why don't we see BW based ISIS topologies, but we do see OSPF? I think it is status quo bias, because vendors offer OSPF with this default, is must make sense. -- ++ytti _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/