[j-nsp] Topology failure on EX4200

Victor Sudakov vas at mpeks.tomsk.su
Sun Jul 16 11:17:13 EDT 2017

Roger Wiklund wrote:
> > There is a ring of EX4200 switches, please look at http://noc.sibptus.ru/jun1.png
> >
> > If MUX1 fails, the MSTP topology adjusts and the PCs continue to see
> > one another just fine.
> >
> > However, some switches become inaccessible in the management vlan
> > (vlan3 in this example). For example, you can still ping
> > from, but not from
> >
> > One important note. If MUX1 fails, the corresponding interfaces on
> > and don't go down, it is only the traffic
> > (including BPDUs) that stops flowing through the mux.
> >
> > If I shutdown the corresponding interfaces on and
> > (or use OAM to shutdown the interfaces automatically when
> > the mux fails), the problem disappears and I can ping any switch from
> > any switch.
> >
> > What's the theory behind this?
> >
> > "clear arp" and "clear ethernet-switching table" don't fix the
> > problem.
> Have you configured loop protection?
> https://www.juniper.net/documentation/en_US/junos/topics/example/stp-loop-protection-qfx-series.html

Dear Roger,

I have configured OAM (link-down on link-adjacency-loss) which helped.

But I'm wondering why the situation in question was happening without
the interfaces going physically down. 

> On a design note, why not use Virtual Chassis instead?

Sorry, I don't understand. Virtual Chassis uses a special short cable,
doesn't it? My switches are not located nearby enough to use that
cable. In fact, they are connected by multiplexers and can be far
away from one another.

Victor Sudakov,  VAS4-RIPE, VAS47-RIPN

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