Spanning tree cost question

Unanswered Question
Mar 2nd, 2010

Hi all,

I did a little network diagram and I am hoping somebody can help.

http://img.photobucket.com/albums/v652/mypersonalpics/f34b1916.jpg

As you can see from my diagram, I have 2 core devices which are 6509's and then connected directly to SW1 and SW4, I have 4 3560's. The switches are daisy chained using cooper. I have reduant links on SW1 and SW4 yet I only want to use the primary link unless it fails switch to the secondary link. For this I am using the command "spanning-tree cost 25" on SW4 and on int g0/3 which faces to R2. With my network monitoring software, I am still seeing traffic coming in (recieve) the g0/3 on SW4 yet not going out. I am wondering if the cost is not set properly or if maybe I am doing it the wrong way all together or maybe if this over 100 mb/sec traffic on the port which is in "blocked" state is normal.

Any help is appreciated.

Thanks

I have this problem too.
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peter.troster Tue, 03/02/2010 - 11:26

Vlan                   Root ID          Cost  Time Age Dly  Root Port
---------------- -------------------- ------ ----- --- ---  ----------------
VLAN0010          8193 00d0.0036.0400     12    2   20  15  Gi0/4
VLAN0500          8595 00d0.0036.0400     12    2   20  15  Gi0/4

is the output I get. Thanks

peter.troster Tue, 03/02/2010 - 11:39

SW1

VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    8193
             Address     00d0.0036.0400
             Cost        4
             Port        27 (GigabitEthernet0/3)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0013.c3b2.9b80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/3            Root FWD 4         128.27   P2p
Gi0/4            Desg FWD 4         128.28   P2p

SW2

VLAN0010
  Spanning tree enabled protocol rstp
  Root ID    Priority    8193
             Address     00d0.0036.0400
             Cost        12
             Port        1 (GigabitEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0018.189f.0d80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Root FWD 4         128.1    P2p Peer(STP)

Gi0/4            Desg FWD 4         128.28   P2p

SW3

VLAN0010
   Spanning tree enabled protocol ieee
   Root ID    Priority    8193
              Address     00d0.0036.0400
              Cost        8
              Port        2 (GigabitEthernet0/2)
              Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
              Address     0013.c3e0.2400
              Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
              Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/1            Desg FWD 4         128.1    P2p
Gi0/2            Root FWD 4         128.2    P2p
Gi0/3            Desg FWD 4         128.27   P2p

SW4

VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    8193
             Address     00d0.0036.0400
             Cost        12
             Port        28 (GigabitEthernet0/4)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0013.c3e0.2080
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/3            Altn BLK 25        128.27   P2p
Gi0/4            Root FWD 4         128.28   P2p

Jon Marshall Tue, 03/02/2010 - 11:42

Peter

Sorry i actually meant the 4 switches as in R1/R2 and SW1/SW4. However it doesn't matter because you can see gi0/3 on SW4 is blocked so the link between SW4 and R2 is indeed not forwarding traffic.

Note that at the R2 end it will not necessarily be blocking, it doesn't have to be to break the loop because gi0/3 being blocked breaks the loop. So you will see traffic coming in in gi0/3 but it is not forwarded. It will be control traffic mainly such as STP BPDUs.

Jon

peter.troster Tue, 03/02/2010 - 11:45

John, Sorry for the mis understanding. I see it is being blocked however I still see traffic going upwards of 200 MB/sec at times but it's recieve only.So this is probably because R2 is trying to send traffic to SW4 and it is being blocked? So the command "spanning-tree cost 25" is coreect and not much else I can do?

Gareth, R1 would be the root bridge.

Thanks for the replies guys

Jon Marshall Tue, 03/02/2010 - 11:48

Peter

From R1 and R2 can you post the same ie. "sh spanning-tree vlan 10"

Jon

peter.troster Tue, 03/02/2010 - 11:51

R1

VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    8193
             Address     00d0.0036.0400
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    8193   (priority 8192 sys-id-ext 1)
             Address     00d0.0036.0400
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 480

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/3               Desg FWD 4         128.3    P2p
Gi1/4               Desg FWD 4         128.4    P2p
Gi1/5               Desg FWD 4         128.5    P2p
Gi1/6               Desg FWD 4         128.6    P2p
Gi1/10              Desg FWD 4         128.10   P2p
Gi5/1               Desg FWD 4         128.513  P2p
Gi6/44              Desg FWD 4         128.684  P2p
Gi7/5               Desg FWD 4         128.773  P2p

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------

Gi7/7               Desg FWD 4         128.775  P2p
Po1                 Desg FWD 1         128.1665 P2p
Po9                 Desg FWD 3         128.1666 P2p
Po11                Desg FWD 3         128.1669 P2p
Po3                 Desg FWD 3         128.1670 P2p
Po6                 Desg FWD 3         128.1673 P2p
Po10                Desg FWD 3         128.1675 P2p

R2

VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    8193
             Address     00d0.0036.0400
             Cost        1
             Port        1665 (Port-channel1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    16385  (priority 16384 sys-id-ext 1)
             Address     00d0.0038.4c00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 480

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/3               Desg FWD 4         128.3    P2p
Gi1/4               Desg FWD 4         128.4    P2p
Gi1/5               Desg FWD 4         128.5    P2p
Gi1/6               Desg FWD 4         128.6    P2p
Gi1/10              Desg FWD 4         128.10   P2p
Gi5/2               Desg FWD 4         128.514  P2p
Gi6/44              Desg FWD 4         128.684  P2p

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------

Po1                 Root FWD 1         128.1665 P2p
Po9                 Desg FWD 3         128.1668 P2p
Po11                Desg FWD 3         128.1669 P2p
Po3                 Desg FWD 3         128.1670 P2p
Po6                 Desg FWD 3         128.1673 P2p
Po10                Desg FWD 3         128.1674 P2p
Po12                Desg FWD 3         128.1676 P2p

Here is the info

Jon Marshall Tue, 03/02/2010 - 12:09

Peter

Apologies, which ports from R1 and R2 connect to SW1 and SW4 ?

If SW4 gi0/3 to R2 is blocked then R2 should not be learning any of the mac-addresses from SW1 -> SW4 from that link so all traffic to clients on your 4 SW switches from R2 should go via the interconnect to R1.

Can you post from R2 the output of "sh mac-address-table dynamic vlan 10 all"

Jon

peter.troster Tue, 03/02/2010 - 12:13

Hi John,

I do know what you mean and I find it interesting also th. R2 connects to SW4 via G1/5 and SW1 connects to R1 via G1/5 also

Here is the results of sh mac-address-table dynamic vlan 10 all on R2

sh mac-address-table dynamic vlan 10 all
Legend: * - primary entry
        age - seconds since last seen
        n/a - not available

  vlan   mac address     type    learn     age              ports
------+----------------+--------+-----+----------+--------------------------
Module 4:
*    1  0022.bd1b.7c29   dynamic  Yes         10   Po1
     1  0023.5d14.07af   dynamic  Yes        160   Po12
*    1  001d.b3fd.4600   dynamic  Yes         45   Po1
     1  0023.5d14.07b0   dynamic  Yes        160   Po12
     1  001f.288e.c180   dynamic  Yes        160   Gi1/3
     1  0023.5d14.07c0   dynamic  Yes         25   Po12
*    1  00d0.0036.0400   dynamic  Yes          5   Po1
     1  0019.e878.7b40   dynamic  Yes         55   Gi5/2
Active Supervisor:
     1  0022.bd1b.7c29   dynamic  Yes        195   Po1
*    1  0023.5d14.07af   dynamic  Yes         10   Po12
     1  001d.b3fd.4600   dynamic  Yes        195   Po1
*    1  0023.5d14.07b0   dynamic  Yes         10   Po12
*    1  001f.288e.c180   dynamic  Yes         55   Gi1/3
*    1  0023.5d14.07c0   dynamic  Yes         25   Po12
     1  00d0.0036.0400   dynamic  Yes         35   Po1
*    1  0019.e878.7b40   dynamic  Yes         60   Gi5/2

contech-nelsong Tue, 03/02/2010 - 12:15

Is VLAN 500 configured the same as VLAN 10?

Is there any untagged traffic on the network?

peter.troster Tue, 03/02/2010 - 12:18

Hey,

No vlan 500 isn't the same as vlan 10. Vlan 10 is mostly the admin vlan and vlan 500 is the edge vlan for users of the 1st floor. No un-tagged traffic on the network and vlan 1 is shutdown

Jon Marshall Tue, 03/02/2010 - 12:18

Peter

So not traffic is being sent to clients via SW4 from the output. I'm assuming that Po1 or Po12 is the interconnect ?

So the question remains what is the traffic. Perhaps you could also look at "sh spanning-tree vlan 500" to make sure that no traffic should be forwarded on the gi1/5 link as well.

If not then it may be worth spanning the port gi1/5 or the port gi0/3 on SW4 to see exactly what is accounting for the traffic.

Jon

peter.troster Tue, 03/02/2010 - 12:24

Hi John,

Yes Po1 is the interconnect from R1 and R2 and I have done sh span vlan 500 across all switches and compared as I previously have with vlan 10 with a co-worker and we see no issues. As per spanning port, a co-worker suggested that to the network admin yet there is limitations to how many we can do and we are currently spanning some ports for more serious issues until tomorrow night so possible tomorrow night I will switch it and sniff some traffic and possible see what is what. My purpose here was that the config was configured properly as I have done the same in lab trying to replicate the same issue and I am not able to and there is zero traffic when using a traffic genorator on the test lab.

Thanks

Jon Marshall Tue, 03/02/2010 - 12:31

Peter

The output of the commands you posted show that blocking is occuring where you want it to and that client mac-addresses are being learnt via R1 so i would say from what we can see you have configured things correctly.

Labs always produce slightly different results

Let me know how you get on if you decide to SPAN the port.

Jon

peter.troster Tue, 03/02/2010 - 12:35

Thanks for the help Jon, I really appreicate it. If I am able to span the port, I will do some more work and let you know of my findings. As for the lab, everything always works as it is suppose to in the labs so this is no different as I have learnt with my little experience.

Thanks again

gianluca2891 Tue, 03/02/2010 - 12:40

If there is a high level of multicast (or broadcast) traffic in the network, it ma be the incoming one you see on the blocked interface.

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