2

I have two 3560 switches, and I have 2 uplinks. The goal is to make one link green on both ports on each switch, and the other link amber (standby), so when I pull the active green link out, the other standby link would take 30 seconds to be new active link. I am lost on what I am missing. I made a root switch and the VLANs and everything. I'mot sure how I make one link active and the other standby,

SleepyMan:

second#sh span

VLAN0005
  Spanning tree enabled protocol ieee
  Root ID    Priority    28677
             Address     001a.e3cd.9e80
             Cost        19
             Port        26 (GigabitEthernet0/26)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28677  (priority 28672 sys-id-ext 5)
             Address     0023.abcd.b900
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/26           Root FWD 19         32.26   P2p
Gi0/28           Altn BLK 19        128.28   P2p


VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    28682
             Address     001a.e3cd.9e80
             Cost        19
             Port        26 (GigabitEthernet0/26)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28682  (priority 28672 sys-id-ext 10)
             Address     0023.abcd.b900
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/26           Root FWD 19         32.26   P2p
Gi0/28           Altn BLK 19        128.28   P2p


VLAN0015
  Spanning tree enabled protocol ieee
  Root ID    Priority    28687
             Address     001a.e3cd.9e80
             Cost        19
             Port        26 (GigabitEthernet0/26)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28687  (priority 28672 sys-id-ext 15)
             Address     0023.abcd.b900
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/26           Root FWD 19         32.26   P2p
Gi0/28           Altn BLK 19        128.28   P2p


VLAN0020
  Spanning tree enabled protocol ieee
  Root ID    Priority    28692
             Address     001a.e3cd.9e80
             Cost        19
             Port        26 (GigabitEthernet0/26)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28692  (priority 28672 sys-id-ext 20)
             Address     0023.abcd.b900
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/26           Root FWD 19         32.26   P2p
Gi0/28           Altn BLK 19        128.28   P2p

second#





new#sh span

VLAN0005
  Spanning tree enabled protocol ieee
  Root ID    Priority    28677
             Address     001a.e3cd.9e80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28677  (priority 28672 sys-id-ext 5)
             Address     001a.e3cd.9e80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/24           Desg FWD 19         32.26   P2p
Fa0/26           Desg FWD 19        128.30   P2p


VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    28682
             Address     001a.e3cd.9e80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28682  (priority 28672 sys-id-ext 10)
             Address     001a.e3cd.9e80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/24           Desg FWD 19         32.26   P2p
Fa0/26           Desg FWD 19        128.30   P2p


VLAN0015
  Spanning tree enabled protocol ieee
  Root ID    Priority    28687
             Address     001a.e3cd.9e80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28687  (priority 28672 sys-id-ext 15)
             Address     001a.e3cd.9e80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/24           Desg FWD 19         32.26   P2p
Fa0/26           Desg FWD 19        128.30   P2p


VLAN0020
  Spanning tree enabled protocol ieee
  Root ID    Priority    28692
             Address     001a.e3cd.9e80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    28692  (priority 28672 sys-id-ext 20)
             Address     001a.e3cd.9e80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/24           Desg FWD 19         32.26   P2p
Fa0/26           Desg FWD 19        128.30   P2p
  • You need to describe this a little better. Are the two switches connecting to each other, or are they linking to something else? – Ron Maupin Jun 21 '16 at 15:32
  • A diagram would help. – Ron Trunk Jun 21 '16 at 15:38
  • The two switches are connecting to eachother with 2 ethernet cables plugged in to eachother( 2 uplinks) , they are both 3560 switches I have made .1q trunks on both cables on both switches – Stan234 Jun 21 '16 at 15:45
  • @RonTrunk so it appears that i was speaking about HSRP, do you know in context with what im trying to achieve to apply this? – Stan234 Jun 23 '16 at 13:25
  • I think you should ask a new question about HSRP. – Ron Trunk Jun 23 '16 at 15:21
3

There is nothing you need to do -- the switches are already running spanning tree and one port (G0/28 on the 2nd switch) is blocking.

But:

A preferred way to configure this is to create a port-channel between the two switches. The port channel combines the two physical interfaces into one logical interface. You get twice the bandwidth because both links are forwarding, you still get the redundancy, and you don't have the slow convergence times of spanning tree.

Here is a sample. Do the same on both sides.

interface gi 0/26
channel-group 1 mode active
!
interface gi 0/28
channel-group 1 mode active
!
interface port-channel 1
switchport
switchport mode trunk
switcport trunk allowed vlan 10-20
no shut
  • but how can i make the port colour amber(blocked) and green(forwarding) for the links? so when i pull the green forwarding link, it would take 30 seconds for the amber links to turn forwarding – Stan234 Jun 21 '16 at 17:14
  • With a port channel, both links are forwarding and there are no blocked ports. The two links act as one logical link. – Ron Trunk Jun 21 '16 at 17:16
  • Traffic is split between the two links. If one link fails, all traffic flows across the remaining link with no convergence time. – Ron Trunk Jun 21 '16 at 17:17
  • do i do this for both switches? or just the one switch you recomended – Stan234 Jun 21 '16 at 17:19
  • 1
    In that case, go back to your original configuration. That is how it was working originally – Ron Trunk Jun 21 '16 at 18:39
1

From your second switch:

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/26           Root FWD 19        128.26   P2p
Gi0/28           Altn BLK 19        128.28   P2p

It clearly shows that STP is blocking one of the links for that VLAN. If you pull the plug on the forwarding link, STP will converge and begin forwarding on the blocked link. This is what you want, and it is the default behavior.

  • Your right, but I want to have one of the links as amber and the other as green, the blocked links as amber and the listening links as green, how do i do that? – Stan234 Jun 21 '16 at 17:11
  • If the lights don't look right, be sure you are in the right mode (press the mode switch on the front panel). – Ron Trunk Jun 21 '16 at 17:20
1

I think what you are trying to do is choose which port on the two switches to be in a blocking state.

If you have two switches and they are connected to each other with two Ethernet cables, assuming the port speed are the same, which equals same cost, spanning tree will choose which path is fastest to the root bridge, by looking at the port priority and port id.

Because the BPDU's coming from the root bridge/Upstream switch that count, you need to adjust the port priority to a lower value on the root bridge side, so that the adjacent switch port will receive a lower port priority BPDU compared to the second Ethernet link, causing this to be the preferred path back to the root bridge. Which in turn would set the second port to be in a blocking state, amber LED.

To view port priority numbers, use the

show spanning-tree command on a Cisco switch.

You should see a list of ports and Prio.Nbr something like 128.24.

To change the port priority, you can use the following:

switch(config-if)# spanning-tree port-priority 32

The priority values are 0, 32, 64, 96, 128, 160, 192, and 224. All other values are rejected.

I hope this helps you on your quest.

SleepyMan

  • hey SleepyMan, i made the port priority for each port on each switch, but all 4 ports are green, could you possibley know why, did you need to see sh span output? – Stan234 Jun 22 '16 at 14:49
  • Did you make sure that the priority are not all the same? Yes please, post the output so I can have a better overview on what is going on. If they are all green then perhaps you are using per vlan spanning tree? – SleepyMan Jun 22 '16 at 15:17
  • how do i use default spanning-tree so how it was set when i first turned the switches on? and i posted the output on the question – Stan234 Jun 22 '16 at 15:29
  • The default mode is PVST+ which seems what you are using. Did you create additional VLAN's? Each time you create a VLAN, a new instance of spanning tree is created. You are no longer seeing amber lights because each VLAN can take a different path and all links can be used. This is a good thing because it means you are not wasting any bandwidth and are not congesting a single link with all the VLAN traffic. If you want to go back to the amber LED status, you will need to remove all your VLAN's except VLAN 1 ( which you can't anyway as it is the default). – SleepyMan Jun 23 '16 at 10:09

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