1.17 Frustration

Hi,

I've configured this as per the solution provided and cannot get the verification to work properly.

Everything looks fine (port-channel up with correct member interfaces, trunking is fine, CDP neighborship between SW1 and SW4), but I cannot get SW1 and SW4 to see each other with STP.

I've created VLAN interface 146 on SW1 and SW4 with IP addresses 155.1.146.11/24 and 155.1.146.44/24 and can ping between them, without any issue.

I'm unable to ping between R1 and R4 though.

I've even reloaded the four switches, but even that doesn't help.

 

Any idea what to troubleshoot next?

 

Thanks

Comments

  • Can you ping from SW1 to R1 or SW4 to R4? Also what is the output of
    show span vlan 146 on SW1 and SW4?

    --
    Brian Dennis, CCIEx5 #2210 (R&S/ISP-Dial/Security/SP/Voice)
    [email protected]

    Internetwork Expert, Inc.
    http://www.INE.com


    On 04/16/2012 10:43 PM, seal1972 wrote:
    > Hi,
    >
    > I've configured this as per the solution provided and cannot get the
    > verification to work properly.
    >
    > Everything looks fine (port-channel up with correct member interfaces,
    > trunking is fine, CDP neighborship between SW1 and SW4), but I cannot
    > get SW1 and SW4 to see each other with STP.
    >
    > I've created VLAN interface 146 on SW1 and SW4 with IP addresses
    > 155.1.146.11/24 and 155.1.146.44/24 and can ping between them, without
    > any issue.
    >
    > I'm unable to ping between R1 and R4 though.
    >
    > I've even reloaded the four switches, but even that doesn't help.
    >
    > Any idea what to troubleshoot next?
    >
    > Thanks
    >
    >
    >
    >
    > Internetwork Expert - The Industry Leader in CCIE Preparation
    > http://www.internetworkexpert.com
    >
    > Subscription information may be found at:
    > http://www.ieoc.com/forums/ForumSubscriptions.aspx
  • Hi Brian,

    Ping from R1 to SW1 and from R4 to SW4 is successful.

    sh span vlan 146 on both switches shows that they see themselves as the root. No other special output there.

     

    Ping from R1 to SW4 VLAN 146 interface doesn't work, although SW4's MAC address appears in the ARP table. Same the other way around.

    When pinging R1 from R4, the ARP table shows an Incomplete address.

     

    Cheers,

     

  • Some additional troubleshooting results.

     

    When shutting down all but one link in the Port-Channel, STP suddenly starts to work properly.

    SW4 becomes the root and SW1 has Po14 as the port to the root.

    Enabling a second interface in the Port-Channel, keeps a stable environment (SW4 remains the root).

    Enabling a third interface in the Port-Channel (even if it's only on one switch), breaks the environment and suddenly both switches claim to be root.

     

    The only way to get back to a stable environment where SW4 is root, is to disable all but one interfaces in the Port-Channel.

     

    Pretty weird if you ask me.

    Cheers,

  • Hi Seal,

    The sh span vlan 146 should see either SW1 or SW4 as the root bridge and not both. Is your trunking configuration between SW2 and SW3 working correctly and/or the metro VLAN tags exist on switches 2 and 3?

    Would you please paste here the ouptut of your shows commands? sh span, sh ether sum and sh trunk...

    Hi Brian,

    Ping from R1 to SW1 and from R4 to SW4 is successful.

    sh span vlan 146 on both switches shows that they see themselves as the root. No other special output there.

     

    Ping from R1 to SW4 VLAN 146 interface doesn't work, although SW4's MAC address appears in the ARP table. Same the other way around.

    When pinging R1 from R4, the ARP table shows an Incomplete address.

     

    Cheers,

     

     

  • Hi,

    Is this real gear or dynamips? I agree with Ricardo, if you see both switches as the root, then you have a physical or unidirectional link. Are these devices cabled properly? Do you have bpdufilter enabled somewhere?

    Please let us know.

  • Well, the story gets better.

    I've resolved the spanning tree issue...

    How? By changing the system MTU on SW1 and SW4 back to 1500.

    Beats me why this would suddenly allow STP to work properly.

     

    However, verification still fails; R1 is unable to ping R4.

    I've done some simple ARP debugging and when I ping from R1 to R4, I see nothing on R4.

    The other way around though, I can see R1 receive and respond to R4's ARP packets.

    SW1 has both R1 and R4 MAC addresses in CAM, SW4 doesn't have R1.

     

    Not sure if my setup is part of the issue (I would say not).

    I've got 4 3550 switches, plugged into a server with 12 NICs, running the routers with Dynamips.

     

    Any more help would be much appreciated.

    And ahm... Happy to post the output of show commands, if these show commands aren't already covered in the solution guide.

  • I see that you're having fun with this one ;-)

    If you want the 802.1q tunneling working properly you need the mtu changed to 1504 on switches 2&3

    And any show commands would still be helpful even though you've a topology matching the scenario on Vol.1.

    And which IOS version are you running on your switches?

    Well, the story gets better.

    I've resolved the spanning tree issue...

    How? By changing the system MTU on SW1 and SW4 back to 1500.

    Beats me why this would suddenly allow STP to work properly.

     

    However, verification still fails; R1 is unable to ping R4.

    I've done some simple ARP debugging and when I ping from R1 to R4, I see nothing on R4.

    The other way around though, I can see R1 receive and respond to R4's ARP packets.

    SW1 has both R1 and R4 MAC addresses in CAM, SW4 doesn't have R1.

     

    Not sure if my setup is part of the issue (I would say not).

    I've got 4 3550 switches, plugged into a server with 12 NICs, running the routers with Dynamips.

     

    Any more help would be much appreciated.

    And ahm... Happy to post the output of show commands, if these show commands aren't already covered in the solution guide.

     

  • Hi Ricardo,


    Your definition of fun must be the opposite of mine...

    I'm running c3550-ipservicesk9-mz.122-44.SE6.bin on all four switches. SW1 is a normal 3550, the other 3 are PoE 3550s. I haven't found any bugs, if that's what you're up to.

     

    As for the output of show commands... I find them pretty useless, since they only show you the obvious.

    But hey... you asked for it:

     

    Trunk between SW2 and SW3 up and running as per required:

    Rack1SW2#sh int trunk

    Port        Mode             Encapsulation  Status        Native vlan
    Fa0/16      on               802.1q         trunking      1

    Port        Vlans allowed on trunk
    Fa0/16      1-4094

    Port        Vlans allowed and active in management domain
    Fa0/16      1,100,200,300

    Port        Vlans in spanning tree forwarding state and not pruned
    Fa0/16      1,100,200,300

    Rack1SW3#sh int trunk

    Port        Mode             Encapsulation  Status        Native vlan
    Fa0/16      on               802.1q         trunking      1

    Port        Vlans allowed on trunk
    Fa0/16      1-4094

    Port        Vlans allowed and active in management domain
    Fa0/16      1,100,200,300

    Port        Vlans in spanning tree forwarding state and not pruned
    Fa0/16      1,100,200,300

     

    Trunk between SW1 and SW4 up and running as per required:

    Rack1SW1#sh int trunk

    Port        Mode             Encapsulation  Status        Native vlan
    Po14        on               802.1q         trunking      1

    Port        Vlans allowed on trunk
    Po14        1-4094

    Port        Vlans allowed and active in management domain
    Po14        1,146

    Port        Vlans in spanning tree forwarding state and not pruned
    Po14        1,146

    Rack1SW4#sh int trun

    Port        Mode             Encapsulation  Status        Native vlan
    Po14        on               802.1q         trunking      1

    Port        Vlans allowed on trunk
    Po14        1-4094

    Port        Vlans allowed and active in management domain
    Po14        1,146

    Port        Vlans in spanning tree forwarding state and not pruned
    Po14        1,146

     

    Port-Channel 14 up on both SW1 and SW4, with correct member interfaces:

    Rack1SW1#sh eth sum
    Flags:  D - down        P - bundled in port-channel
            I - stand-alone s - suspended
            H - Hot-standby (LACP only)
            R - Layer3      S - Layer2
            U - in use      f - failed to allocate aggregator

            M - not in use, minimum links not met
            u - unsuitable for bundling
            w - waiting to be aggregated
            d - default port


    Number of channel-groups in use: 1
    Number of aggregators:           1

    Group  Port-channel  Protocol    Ports
    ------+-------------+-----------+-----------------------------------------------
    14     Po14(SU)        PAgP      Fa0/13(P)   Fa0/14(P)   Fa0/15(P)  

    Rack1SW4#sh eth sum
    Flags:  D - down        P - bundled in port-channel
            I - stand-alone s - suspended
            H - Hot-standby (LACP only)
            R - Layer3      S - Layer2
            U - in use      f - failed to allocate aggregator

            M - not in use, minimum links not met
            u - unsuitable for bundling
            w - waiting to be aggregated
            d - default port


    Number of channel-groups in use: 1
    Number of aggregators:           1

    Group  Port-channel  Protocol    Ports
    ------+-------------+-----------+-----------------------------------------------
    14     Po14(SU)        PAgP      Fa0/19(P)   Fa0/20(P)   Fa0/21(P)  

    CDP working between SW1 and SW4:

    Rack1SW1#sh cdp nei
    Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                      S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

    Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
    Rack1SW4         Fas 0/15          154           S I      WS-C3550- Fas 0/21
    Rack1SW4         Fas 0/14          154           S I      WS-C3550- Fas 0/20
    Rack1SW4         Fas 0/13          155           S I      WS-C3550- Fas 0/19

    Rack1SW4#sh cdp nei
    Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                      S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

    Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
    Rack1SW1         Fas 0/19          133           S I      WS-C3550- Fas 0/13
    Rack1SW1         Fas 0/21          130           S I      WS-C3550- Fas 0/15
    Rack1SW1         Fas 0/20          130           S I      WS-C3550- Fas 0/14

    STP working properly (finaly):

    Rack1SW1#sh span vlan 146

    VLAN0146
      Spanning tree enabled protocol ieee
      Root ID    Priority    32914
                 Address     000e.d74f.5100
                 Cost        9
                 Port        65 (Port-channel14)
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

      Bridge ID  Priority    32914  (priority 32768 sys-id-ext 146)
                 Address     0011.93af.e680
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                 Aging Time 300

    Interface           Role Sts Cost      Prio.Nbr Type
    ------------------- ---- --- --------- -------- --------------------------------
    Fa0/1               Desg FWD 19        128.1    P2p
    Po14                Root FWD 9         128.65   P2p

    Rack1SW4#sh span vlan 146

    VLAN0146
      Spanning tree enabled protocol ieee
      Root ID    Priority    32914
                 Address     000e.d74f.5100
                 This bridge is the root
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

      Bridge ID  Priority    32914  (priority 32768 sys-id-ext 146)
                 Address     000e.d74f.5100
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                 Aging Time 300

    Interface           Role Sts Cost      Prio.Nbr Type
    ------------------- ---- --- --------- -------- --------------------------------
    Fa0/4               Desg FWD 19        128.4    P2p
    Po14                Desg FWD 9         128.65   P2p

     

    Let the fun begin...

     

     

     


  • Believe me Seal this opposite of fun will make you a stronger engineer.

    As per the show commands on your switches the L2 seems to be functional. And lets say that you remove the 802.1q tunneling configuration between SW2 and 3 and leave only the trunking between switches and create vlan 146 on all of them, will R1 and R4 ping each other? 

     


  • Hi Ricardo,


    I'll give it a go tonight.

    I don't think there's an issue in my lab, though.

    FYI: I've already went through WB1-4 about 2 years ago, without too many issues. I haven't touched my lab since (the arrival of offspring is to blame for that).

  • Ok thats fine, let us know your progress then.

    Hi Ricardo,


    I'll give it a go tonight.

    I don't think there's an issue in my lab, though.

    FYI: I've already went through WB1-4 about 2 years ago, without too many issues. I haven't touched my lab since (the arrival of offspring is to blame for that).

     

  • Argh.

    What can I say? Frustration all over!!!

     

    Started up my lab and of course, being a good engineer, I first checked if the problem was still around.

    Of course, now I could ping between R1 and R4!!!

     

    I have admit, Ricardo,

    Issues like these can be fun... when they involve troubleshooting, finding mistakes and resolving the issue by logically deducting what the cause of the issue is.

    In this particular case, I don't like it a single bit that STP didn't work properly with the system MTU set to 1504 on SW1 and S4 (that shouldn't really matter, IMO) and that the ping between R1 and R4 is suddenly successful after a reload of the lab.

    However, thanks for encouraging me to look further; without your endorsement, I would probably have skipped the issue and moved on to the next task.

     

    Cheers,

  • Thats awesome news Seal!

    And for more fun try to set a time (say 10 minute) to solve these issues, also on the exam make sure you don't spend that much time on issues like that instead skip them and try to solve later ;-)

     

  • Trust me, I've sat the exam, and I'm pretty sure basic connectivity is a major requirement to pass.

    Not spending much time on an issue like this, skip it and try to resolve later is not really an option.

Sign In or Register to comment.