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mrshabbs
Beginner

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

8 REPLIES 8
Angello1812
Beginner

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

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.

Peter Paluch
Hall of Fame Cisco Employee

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

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


Peter Paluch
Hall of Fame Cisco Employee

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

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

Peter Paluch
Hall of Fame Cisco Employee

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

sabbinanti
Beginner

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