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New Member

Spanning-Tree help needed

Hi all, I have 4 switches  (2 x 2960 & 2 x 3500) connected together in 1 big loop (1 to 2 to 3 to 4) using fibre on the gigabit interface ports. My question relates to spanning-tree.

Switch 1 is the root bridge. Between switch 1 and switch4  i cannot establish lights on the interfaces g 0/1 (these interfaces are directly connected with fibre). Below is the output from both switches:-

       

switch1#show spanning-tree interface g 0/1
no spanning tree info available for GigabitEthernet0/1

switch4#
Interface Gi0/1 (port 40) in Spanning tree 1 is down
  Port path cost 4, Port priority 128
  Designated root has priority 24577, address d824.bd16.b500
  Designated bridge has priority 32768, address 0006.2828.d180
  Designated port is 40, path cost 12
  Timers: message age 0, forward delay 0, hold 0
  BPDU: sent 3, received 667

I would have thought one interface (int g 0/1 on switch 1 or switch4) would be in block status and the other remaining interface to be in fwd status. However as you can see from the above output there is no spanning-tree info available on switch1. On switch4 the interface is showing as down, which indicates there is no physical connection? I have replaced the fibre lead and the gbic modules in sw1 & sw4.

The result here is I have no redundant link (there is already a break between switch1 & switch4 becuase of this issue)

Can anyone shed any light on this please

Everyone's tags (1)
8 REPLIES
New Member

Re: Spanning-Tree help needed

Hi Shane,

I dont exactly know how to solve your problem, just wondering - if SW1 is root and is directly connected to SW4, you should expect Gi0/1 on SW1 to be designated - FWD state, but at SW4 Gi0/1 will be root port, so in FWD state too (not blocked). Correct me somebody if I am wrong.

Have you tried to change fiber to classical cross-over cable? Maybe it would also help to look in output of show int gi0/1 at both switches while they are connected and expected to work. Do these interterfaces work well in general?

Best Regards

Jan Janovic

New Member

Spanning-Tree help needed

Thanks for the reply Jan. I have checked the interfaces g 0/1 on switch1 and also switch4 as suggested, both are showing as down. I have replaced switch4, replaced the fibre connecting switch 1 and switch4 and replaced both gbics used on the interfaces g 0/1 of switch 1 & switch4. Interface g 0/2 on switch1 (connected to switch2) is DESG fwd.

Cisco Employee

Spanning-Tree help needed

Hello Shane,

Jan is heading in the correct direction - the up/down status of your ports is something that precedes STP, and is related to basic Layer1/Layer2 connectivity. If your ports are reported as down then they basically tell you they are disconnected - not blocked by STP.

Can you please post the complete output of the following commands from both Sw1 and Sw4?

  • show interface gi0/1
  • show interface status | inc Gi0/1
  • show interface gi0/1 capabilities
  • show run int gi0/1

Thank you!

Best regards,

Peter

New Member

Spanning-Tree help needed

Hello Peter, thanks for the reply. Please see below the outputs of sw1 and sw4 as suggested. On sw4 (3500xl) the cmd "show interface gi0/1 capabilities" is not allowed

SWITCH1#show interface gi0/1

GigabitEthernet0/1 is down, line protocol is down (notconnect)

  Hardware is Gigabit Ethernet, address is d824.bd16.b519 (bia d824.bd16.b519)

  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive not set

  Auto-duplex, Auto-speed, link type is auto, media type is 1000BaseSX SFP

  input flow-control is off, output flow-control is unsupported

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 21w6d, output 21w6d, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/0 (size/max)

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     66734 packets input, 12311737 bytes, 0 no buffer

     Received 3894 broadcasts (1799 multicasts)

     14 runts, 0 giants, 0 throttles

     14 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 1799 multicast, 0 pause input

     0 input packets with dribble condition detected

     168878 packets output, 42300964 bytes, 0 underruns

     0 output errors, 0 collisions, 1 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 PAUSE output

     0 output buffer failures, 0 output buffers swapped out

SWITCH1#show interface status | inc Gi0/1

Gi0/1                        notconnect   1            auto   auto 1000BaseSX SFP

SWITCH1#show interface gi0/1 capabilities

GigabitEthernet0/1

  Model:                 WS-C2960-24PC-L

  Type:                  1000BaseSX SFP

  Speed:                 1000

  Duplex:                full

  Trunk encap. type:     802.1Q

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100)

  Flowcontrol:           rx-(off,on,desired),tx-(none)

  Fast Start:            yes

  QoS scheduling:        rx-(not configurable on per port basis),

                         tx-(4q3t) (3t: Two configurable values and one fixed.)

  CoS rewrite:           yes

  ToS rewrite:           yes

  UDLD:                  yes

  Inline power:          no

  SPAN:                  source/destination

  PortSecure:            yes

  Dot1x:                 yes

  Multiple Media Types:  rj45, sfp, auto-select

SWITCH1#show run int gi0/1

Building configuration...

Current configuration : 36 bytes

!

interface GigabitEthernet0/1

end

switch4#show interface gi0/1

GigabitEthernet0/1 is down, line protocol is down

  Hardware is Gigabit Ethernet, address is 0006.2828.d199 (bia 0006.2828.d199)

  MTU 1500 bytes, BW 0 Kbit, DLY 0 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive not set

  Auto-duplex , 1000Mb/s, media type is SX

  output flow-control is off, input flow-control is off

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 16:19:14, output 16:19:59, output hang never

  Last clearing of "show interface" counters never

  Queueing strategy: fifo

  Output queue 0/40, 0 drops; input queue 0/75, 0 drops

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     2584 packets input, 309915 bytes, 0 no buffer

     Received 2536 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 1702 multicast, 0 pause input

     68 packets output, 12336 bytes, 0 underruns

     0 output errors, 0 collisions, 1 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

switch4#show interface status | inc Gi0/1

Gi0/1                      notconnect   1          Auto    1000 1000BASESX

switch4#show interface gi0/1 capabilities

                                   ^

% Invalid input detected at '^' marker.

switch4#show interface gi0/1  ?

  accounting      Show interface accounting

  crb             Show interface routing/bridging info

  ethernet        Show ethernet vlan type

  fair-queue      Show interface Weighted Fair Queueing (WFQ) info

  flow-control    Show flow control information

  irb             Show interface routing/bridging info

  link-trap       Show interface traps on no link

  mac-accounting  Show interface MAC accounting info

  precedence      Show interface precedence accounting info

  pruning         Show interface pruning information

  random-detect   Show interface Weighted Random Early Detection (WRED) info

  rate-limit      Show interface rate-limit info

  status          Show interface line status

  switchport      L2 interface information

  trbrf           Show BRF tokenring vlan type

  type            Show vlan types

  |               Output modifiers

 

switch4#show run int gi0/1

Building configuration...

Current configuration:

!

interface GigabitEthernet0/1

end


Cisco Employee

Spanning-Tree help needed

Hello Shane,

Thank you for the reply. The output you have posted suggests that there is a basic connectivity problem between your two switches.

The most natural question is whether the fiber and the optical GBICs/SFPs are okay and properly matched. Are you able to verify that each GBIC/SFP is capable of linking up successfully with some other GBIC/SFP that is proved to work? If these modules are using two fibers, you could make a test with looping the GBIC/SFP by interconnecting its Tx and Rx port, however, I recommend caution here - a longer fiber or an attenuator is recommended in order not to overload the Rx detector.

Also, the 1000BaseSX needs multimode fiber to be used - I assume you are using the proper fiber type.

Best regards,

Peter

New Member

Spanning-Tree help needed

Hi Paul

If I swap the 'suspect' fibre, gbic & sfp between sw1 & sw4 with the 'working' fibre, gbic & sfp between sw2 & sw3, the fault remains between sw1 & sw4. The connection between sw2 & sw3 becomes active. This proves there is no fault with the fibre, gbic or sfp. I agree there is a basic layer1 / 2 connectivity issue from the output of the interfaces however I believe I have confimed all hw as working. I will do further testing and keep you updated. Thanks for your help so far

Cisco Employee

Spanning-Tree help needed

Hello Shane,

You're welcome but the "thank you" you gave me is not deserved yet.

As the fault seems to be stuck between Sw1 and Sw4, I am starting to wonder if the SFP/GBIC slot itself (not the transceiver but rather the socket) on either of these switches is working properly. Would either of Sw1/Sw4 Gi0/1 ports come up if it was connected to a different and guaranteedly working fiber port/transceiver? Try to avoid interconnecting Sw1 and Sw4 Gi0/1-s in particular.

Also, can you try using the media-type sfp on the 2960 Gi0/1 port? Are you using genuine Cisco SFP/GBIC?

Best regards,

Peter

New Member

Spanning-Tree help needed

Can you provide the running config for both swithces? All that is needed the the config for the interface on switch 1 connected to switch 4 and the config for the interface on swich 4 connect to switch one.

Regards,

Sebastian

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