[j-nsp] Topology failure on EX4200

[Victor Sudakov]

Dear Colleagues,

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 192.168.1.3
from 192.168.1.2, but not 192.168.1.4 from 192.168.1.2.

One important note. If MUX1 fails, the corresponding interfaces on
192.168.1.2 and 192.168.1.4 don't go down, it is only the traffic
(including BPDUs) that stops flowing through the mux.

If I shutdown the corresponding interfaces on 192.168.1.2 and
192.168.1.4 (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.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
AS43859