[j-nsp] Unequal bandwidth on virtual chassis ports?

[Pavel Lunin]

In fact, the ring is "required" for each type of links: 32/40g stacking
ports, xe and ge separately.

This comes from the underlying ISIS LFA aka VC fast reroute feature. Two
alternative routes are installed into the FIB for each destination, if one
link fails, the corresponding route is withdrawn quickly and the
alternative one is already there, so you don't have to wait while SFP
reconverges. This works only for the same type of links in an LFA pair.

IIRC, VC fast reroute is enabled by default for 40/32G links, for xe and ge
you need to enable it manually.

If you don't have a ring for a given type of VCP links, VC will work
without fast reroute, you'll just have a bit longer outage time in case of
a failure (need to wait until ISIS detects the failure and reconverges).

Regards,
Pavel

26 окт. 2017 г. 11:17 ПП пользователь "Chris Kawchuk" <juniperdude at gmail.com>
написал:

> As VC uses IS-IS as it's underlying protocol (last time I checked), I
> believe there is a metric associated with each VC link. show
> virtual-chassis adjacency/database/etc.. should show those metics.
>
> VC IS-IS will calculate the lowest-metric to the far-end PFE, and use
> that. I also recall that it counts packet-forwarding-engines inside the
> switch itself, and not switches per se as a hop/link count. For example, an
> EX4200 has 3 x PFEs inside the box, and depending on where/how you connect
> the back-side VC cables or front-side revenue ports as VC will affect how
> it sees the topology.
>
> VC will not load balance across unequal-costs (a-la RSVP-TE or something),
> and doesn't use multiple paths (even if they're ECMP) to the destination
> either last time I played with it; but it's been a while ;)
>
> VCF will do the ECMP-trick, BTW.
>
> - CK.
>
>
> On 27 Oct 2017, at 8:05 am, Jonathan Call <lordsith49 at hotmail.com> wrote:
>
> > Typically when I build virtual chassis I set up the recommended "ring"
> topology and give path an equal amount of bandwidth. Would there be any
> technical problems if I give one of the virtual chassis links more
> bandwidth than the others?
> >
> >
> > The Virtual Chassis Feature Guide for the QFX Series doesn't suggest
> there is anything wrong with this, but it doesn't really discuss the
> scenario either.
> >
> >
> >
> > Jonathan
> >
> >
> >
> >
> >
> >
> >
> >
> >
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