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Spanning tree protocol problem RSTP(wireshark Dump)

Discussion in 'Networking' started by Profess0rX, Jul 27, 2016.

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  1. Profess0rX

    Profess0rX Thread Starter

    Jul 27, 2016
    Hello guys, this is my first post on this forum,
    Ive been working for 3 months in a nice company as a system admin.
    This is a wired connection problem.
    I am fresh out of school and a little bit inexperienced with real networking equipment. I mostly learned with packet tracer and GNS3.

    Ive installed a netgear m4100-POE-26G for the production department, this switch is working in EtherChannel(LACP) with a DELL PowerWare 5524 24 Port.

    The lacp is working really well, the trunk also.

    We run RSTP for spanning tree protocol, when troubleshooting slow network access and Ip phones losing assignation, Ive realised that there is an RSTP election going on. Its now been three weeks that I am working on this problem. I know that the Hello packets(keep alive) are timed a 2 seconds on every switch. The core switch has the priority 0 so the root should not change.

    After Sniffing packet for 10 minutes I have found some FCS errors on all of my RSTP packets.

    If I unplug and replug the Dell switch the problem is gone for a day or two.

    The Dell switch has a Fiber trunk going towards the root bridge. This is the link that would be flopping up and down in the same second, with a STP-Forwarding state message.

    Here I have some of the Rstp packet collected, if you can help me troubleshoot this, I would be very grateful.:flowers:

    No. Time Source Destination Protocol Length Info
    1 0.000000 Dell_b2:38:07 Spanning-tree-(for-bridges)_00 STP 64 RST. TC + Root = 0/0/a0:63:91:9e:60:54 Cost = 2000 Port = 0x8010 [ETHERNET FRAME CHECK SEQUENCE INCORRECT]

    Frame 1: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface 0
    IEEE 802.3 Ethernet
    Destination: Spanning-tree-(for-bridges)_00 (01:80:c2:00:00:00)
    Source: Dell_b2:38:07 (d0:67:e5:b2:38:07)
    Length: 39
    Padding: 00000000000000
    Frame check sequence: 0x00000000 [incorrect, should be 0x4da67cf2]
    [FCS Good: False]
    [FCS Bad: True]
    Logical-Link Control
    Spanning Tree Protocol
    Protocol Identifier: Spanning Tree Protocol (0x0000)
    Protocol Version Identifier: Rapid Spanning Tree (2)
    BPDU Type: Rapid/Multiple Spanning Tree (0x02)
    BPDU flags: 0x5f, Agreement, Learning, Port Role: Designated, Proposal, Topology Change
    Root Identifier: 0 / 0 / a0:63:91:9e:60:54
    Root Path Cost: 2000
    Bridge Identifier: 28672 / 0 / d0:67:e5:b2:37:f7
    Port identifier: 0x8010
    Message Age: 1
    Max Age: 20
    Hello Time: 2
    Forward Delay: 15
    Version 1 Length: 0
  2. zx10guy

    zx10guy Trusted Advisor Spam Fighter

    Mar 30, 2008
    You need to post up your network topology to show how the switches are connected together which one is the root bridge and the priority assigned to that switch.

    Both switches have the capability to have commands issued through a command line. I suggest you use that. I would do a show spanning tree type command to see what the switch reports as its priority and who it identifies as the root bridge. Next I would look through each of the switch ports as there should be a table displayed from the show spanning tree command to see what each port shows as its operating state (ie forwarding, listening, learning, blocking). Next I would look for what the port role is whether the port is showing as a designate, root, alternate, etc. The port on a non root switch which has the shortest pathway to the root bridge switch should have a port role as root. Make sure the port identified as a root port is the right interface.

    I also haven't ever seen a STP priority value set to 0 (zero). The lowest number I've seen used to assign to a root bridge is 4096.

    If you double check everything and it all seems correct, I would implement spanning tree commands on all ports which you don't expect a switch to be plugged in to have settings such as BPDU guard and/or root guard.
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