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MAC flapping issue with VSTP (Cisco and Juniper)

Hi Everyone,

We have Juniper EX 4200 as core switch at two sites connected Cisco  2960s and Cisco 3560s (access layer switches). For even-numbered VLANs,  one Juniper switch is root bridge and for odd-numbered VLANs, other  Juniper switch is the root bridge.

We have Cox and Verizon Metro-E links connecting core switches (Juniper EX 4200 at both sites).

I want to do VLAN load sharing using VSTP but somehow it is not  working as expected. I want to pass some VLANs through COX and some  through Verizon. When there is any issue with Cox, all VLAN traffic pass  through Verizon and vice-versa. RSTP is also enabled on both Juniper  switches.

I see MAC flapping in log messages on all Cisco access layer switches  when I bring up both Metro-E links together. When only Cox is  connected, everything works fine. When only Verizon is connected,  everything works fine. But when BOTH COX and Verizon are connected,  network gets disrupt and I see MAC flapping on all Cisco switches. All  cisco switches are running PVST.

Anybody knows what is happening  and why VSTP is not working when both COX and VERIZON Metro-E links are active ?

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