Switching

Hi all,

I am facing the following issue: we have a couple of QFX10016 with MC-LAGs configured and we need to connect them to a cloud of Cisco switches without using MC-LAGs.

Spanning-tree is not running on QFXs, while it is running on Cisco side (RPVST+). 

Being spanning-tree disabled, I expected the QFXs to behave transparently in terms of BPDU handling, meaning that when they receive the BPDUs coming from Cisco switches, they should flood them into the vlan as regular mcast traffic, but this is not happening because it seems that the QFX sends the BPDU to the Routing Engine (I saw it through the monitor traffic interface command) which eventually drops the packet.

So I decided to enable spanning-tree, in particular I chose RSTP to follow Juniper Best PRatices saying that MSTP and VSTP shouldn't be used in MC-LAG scenarios (https://www.juniper.net/documentation/us/en/software/junos/mc-lag/topics/concept/best-practices-usage-notes.html), but it worked only for vlan 1, while all other vlans using RPVST+ created a loop since their BPDUs are still not forwarded: if QFXs forwarded the BPDUs, Cisco switches would receive them back and would block ports on their side, but this is not happening.

Is there a way to let the QFX forward Cisco BPDUs without dropping them?

Thanks in advance,

Eridano