I have some Juniper switches (Model: ex4550-32f) connected together with trunk ports.

I want to allow VLAN 6 on all below interfaces because it is the main switch and connected to other switches in other locations with one connection only. Why it is blocked on some interfaces? How can I solve it?

You can see the results below:

J**U-MAIN-CORE-SW# run show spanning-tree interface vlan-id 6
Spanning tree interface parameters for instance 0
Interface    Port ID    Designated      Designated         Port    State  Role
                         port ID        bridge ID          Cost
xe-0/0/0.0     128:513      128:513  32768.5c4527ddd701      2000  FWD    DESG
ge-0/0/1.0     128:514      128:514  32768.5c4527ddd701     20000  BLK    DESG
xe-0/0/2.0     128:515      128:515  32768.5c4527ddd701      2000  BLK    DESG
xe-0/0/27.0    128:540      128:540  32768.5c4527ddd701      2000  BLK    DESG
xe-0/0/31.0    128:544       128:53  32769.6899cd9eed00      2000  FWD    ROOT**
  • 1
    We need to see a network diagram showing the other switches that are connected to it. Also please post the relevant parts of the configuration.
    – Ron Trunk
    Feb 1 '16 at 13:08
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 7 '17 at 18:57

It's blocked on some ports because this switch is not the root switch for that VLAN. The root switch for VLAN 6 is connected (directly, or through another switch) to port xe-0/0/31.0.

If you want this switch to be the root switch, you need to lower the Bridge ID. You left the priority at the default of 32768. I assume you left all the switches at the default, and the root bridge will be determined by the lowest MAC address. You should lower the priority to determine the root, otherwise the determination is left to the lowest MAC address.


Configuring Rapid Spanning Tree Protocol (RSTP)

The root bridge is the ONLY switch in the layer 2 topology, rather it be STP, RSTP or VSTP (VLAN STP) that will forward traffic out on all ports. The root bridge however is elected by the lowest priority and/or the lowest MAC address.

The root bridge however is elected by the lowest priority and/or the lowest MAC address.

It is best practice to set your root switch as 4096 and the backup root switch as 8192.

show spanning-tree bridge
show spanning-tree interface brief 
set protocols rstp bridge-priority #
set interfaces ge-0/0/23.0 family ethernet-switching port-mode trunk native-vlan-id 6 vlan members [allowed vlans]
show ethernet-switching interface ge-0/0/23 detail
show ethernet-switching interfaces detail | match Trunk
show ethernet-switching interfaces detail <interface-name>

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