This is a pretty simple setup. With normal spanning tree one of the redundant links will be blocked. So in order to make use of the blocked port, you can load balance traffic using MSTP (Multiple Spanning Tree). First the basic setup.
user@SW-A# show interfaces ge-0/0/42
description to-SW-B-0/0/42;
unit 0 {
family ethernet-switching {
port-mode trunk;
vlan {
members all;
}
}
}
user@SW-A# show interfaces ge-0/0/47
description to-SW-B-ge-0/0/47;
unit 0 {
family ethernet-switching {
port-mode trunk;
vlan {
members all;
}
}
}
user@SW-A# show vlans
v100 {
vlan-id 100;
}
v200 {
vlan-id 200;
}
user@SW-A# show protocols mstp
msti 1 {
vlan 100-199;
}
msti 2 {
vlan 200-299;
}
user@SW-A# run show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32768.50c58dab9081 20000 FWD DESG
ge-0/0/47.0 128:560 128:560 32768.50c58dab9081 20000 FWD DESG
Spanning tree interface parameters for instance 1
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32769.50c58dab9081 20000 FWD DESG
ge-0/0/47.0 128:560 128:560 32769.50c58dab9081 20000 FWD DESG
Spanning tree interface parameters for instance 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32770.50c58dab9081 20000 FWD DESG
ge-0/0/47.0 128:560 128:560 32770.50c58dab9081 20000 FWD DESG
user@SW-B# show interfaces ge-0/0/42
description to-SW-A-0/0/42;
unit 0 {
family ethernet-switching {
port-mode trunk;
vlan {
members all;
}
}
}
user@SW-B# show interfaces ge-0/0/47
description to-SW-A-ge-0/0/47;
unit 0 {
family ethernet-switching {
port-mode trunk;
vlan {
members all;
}
}
}
user@SW-B# show protocols mstp
msti 1 {
vlan 100-199;
}
msti 2 {
vlan 200-299;
}
user@SW-B# run show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32768.50c58dab9081 20000 FWD ROOT
ge-0/0/47.0 128:560 128:560 32768.50c58dab9081 20000 BLK ALT
Spanning tree interface parameters for instance 1
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32769.50c58dab9081 20000 FWD ROOT <<<<< NOTE
ge-0/0/47.0 128:560 128:560 32769.50c58dab9081 20000 BLK ALT
Spanning tree interface parameters for instance 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32770.50c58dab9081 20000 FWD ROOT
ge-0/0/47.0 128:560 128:560 32770.50c58dab9081 20000 BLK ALT
SW-A is root bridge because of lowest mac address.
As you can see on SW-B, port ge-0/0/47 is blocked for all tagged and untagged traffic.
There are two ways to influence spanning tree to change the forwarding state.
First, to affect the forwarding state of a particular spanning tree instance, you can use priorities on the root switch. This is useful to load balance traffic for under utilized links.
user@SW-A# set protocols mstp msti 1 interface ge-0/0/42 priority 240
On the remote switch SW-B
user@SW-B# run show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32768.50c58dab9081 20000 FWD ROOT
ge-0/0/47.0 128:560 128:560 32768.50c58dab9081 20000 BLK ALT
Spanning tree interface parameters for instance 1
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 240:555 32769.50c58dab9081 20000 BLK ALT <<<<<<<< Here we block traffic
ge-0/0/47.0 128:560 128:560 32769.50c58dab9081 20000 FWD ROOT <<<< now traffic will be forwarded on this interface for vlans in the range 100-199
Spanning tree interface parameters for instance 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32770.50c58dab9081 20000 FWD ROOT
ge-0/0/47.0 128:560 128:560 32770.50c58dab9081 20000 BLK ALT
The second method is to affect the traffic by adjusting the cost locally
user@SW-B# set protocols mstp msti 2 interface ge-0/0/47 cost 10000
user@SW-B# commit
configuration check succeeds
commit complete
user@SW-B# run show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32768.50c58dab9081 20000 FWD ROOT
ge-0/0/47.0 128:560 128:560 32768.50c58dab9081 20000 BLK ALT
Spanning tree interface parameters for instance 1
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 240:555 32769.50c58dab9081 20000 BLK ALT
ge-0/0/47.0 128:560 128:560 32769.50c58dab9081 20000 FWD ROOT
Spanning tree interface parameters for instance 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/42.0 128:555 128:555 32770.50c58dab9081 20000 BLK ALT
ge-0/0/47.0 128:560 128:560 32770.50c58dab9081 10000 FWD ROOT <<<<<<<< HERE
Now only untagged traffic will forward over the ge-0/0/42 interface.
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