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Cisco WAN Switching Modules

Troubleshooting PVC Problems

Document ID: 7115

Updated: Apr 17, 2009

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Introduction

This document describes how to troubleshoot permanent virtual circuit (PVC) problems in a Cisco IGX 8400 or BPX 8600 series switch running 9.1 Switch Software or later.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on this software and hardware:

  • Switch Software 9.1 and later

  • IGX 8400 Universal Switching Module (UXM)

  • BPX 8600 Broadband Switch Module (BXM)

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

UXM and BXM Functionality

UXM and BXM modules support ATM Forum compliant traffic between user and network equipment and within Cisco networks. Both modules display statistics for connections whether they are operating in line mode or trunk mode. Based on this functionality, the UXM and BXM can display statistics at each point in a connection path.

Connections are referred to as channels for statistics collection using the dspchstats command. Channel statistics provide information to help troubleshoot network connectivity problems such as excessive delay or one-way traffic on customer premise equipment (CPE). Connections that traverse an IGX or BPX are known as via connections. The diagram below provides an oversimplified example of the terminating and via segments of a connection traversing BPX BXMs.

one_way.gif

The dspchstats command identifies discards on a connection and requires the connection number or trunk identifier to display useful information. The dspchstats command syntax depends upon the connection type as described here:

Segment Command Syntax
terminating dspchstats module_slot.line.vpi.vci , where vpi = virtual path identifier; vci = virtual channel identifier.
via dspchstats module_slot.trunk.lcn , where lcn = logical channel number.

Examine PVC Via Segments

This section assumes that the dspchstats module_slot.line.vpi.vci command does not display discards or congestion at either terminating segment. It also assumes that end-to-end connectivity is slow or successful in only one direction. The connection could be experiencing discards or a stuck-module queue at the via segments.

Complete these steps to isolate the source of the problem:

  1. Identify all connections via segment logical channel numbers.

    The service-level dcct slot.port.vpi.vci command contains multiple screens of information about a specific connection, including six screens for local connections and seven screens for connections routed across a network. The command output depends upon the switch type. The table below provides the equivalent fields for the IGX 8400 and BPX 8600 series switches.

    IGX 8400 BPX 8600
    Master Lcon Index Mstr LCon Idx
    Master Node Number Master Node#
    Slot.port Trunk
    LCN This Chan

    1. Use the dcct slot.port.vpi.vci command and record the following information to evaluate the via segments of the ATM connection used in this example:

      • Logical connection (LCON) number . The LCON is unique per node. A connection only has one pair of LCONs representing the master and slave ends.

      • Master Node Number. Indicated by a 1 in the Master field on the first screen or in the Master Node Number field on the last screen of the dcct slot.port.vpi.vci command. A connection only has one master end representing the node on which the connection was built.

      • Trunk information (slot.port). The trunk information is specific to each end of the trunk.

      • Logical channel number (LCN). The logical number assigned to the connection on the card. A connection has one LCN per card and two LCNs per trunk.

      g4static       TN    StrataCom       IGX 8420  9.2.23    May  18 2000 1131 GMT 
      
      Slot 11  Port 1  VPI.VCI 100.1 LCON# 16  &31875AC4       VC# 16  &3193FA88
      Alloc      1   Bundled    0    MS Cmax,SM 10,10   mir   384000,384000
      Exists     1   Never rtd  0    COS        0       peak  768000,768000
      Master     1   No DC fnd  0    Hops       2       Cmax  200,200
      Local      0   Failed     0    Src dc     10      %Utl  100,100
      Pref only  0   Down,pend  0,0  Snk dc     10      FSTsts     1
      No rt fnd  0   Cur route  PREF Frst Pt,oe 3,3     Route wait 329493477
      Path fail  0   BW needed  No   Bndl Sz,OE 0,0     Cdt reason None
      Derouted   0   baddr type 1    Group num  0       MS PLU,SM  2400,2400
      RrtReq L,G 0,0 acc dev vx 0    VC count   1       MS CLU,SM  1000,1000
      Route CDT  0   Max cost   100  VC index   16      Line rstr  NONE
                                                           RR Group # 10
      Path  63/5 66/4 64                                  Prev LCON  17
      Pref  63/5 66/4 64                                  Next LCON  65535
      
      Slot 11  Port 1  VPI.VCI 100.1LCON# 16  &31875AC4       VC# 16  &3193FA88
      
      !--- Five screens were skipped because they are not used in this document.
      
      
      XLAT DB Ptr          30D2FC5C
      XLAT Entry Ptr       30D0064C
      Slot.port.index      11.5.2
      Sequence Number      6
      State                USED
      LTrk/OE LTrk         6 / 255
      LCN/OE LCN           262 / 0
      xmt/rcv baddr        1 / 2 (Note add 0x1000 for CBA)
      VPC                  0
      Conid                4102
      Master Node Number   64
      Master Lcon Index    16
      Vc Index             16
                                                                                
      Last Command dcct 11.2.100.100
      
    2. Use the dspnds +n command to translate from node number to node name.

      g4static TN Service IGX 8420 9.2.31 Aug. 28 2000 13:48 GMT 
       NodeName J/ Num
       g5static  /63
       g4static  /64
       b4static  /66
       Last Command: dspnds +n
      

      Important information from the dcct command is highlighted in bold. The Master Node Number and the Master Lcon Index number are required to identify relevant LCNs on a via node. The LCON of a connection on the master node is the Master Lcon Index for the connection through the network. Each connection has many LCNs, including ones for each card it travels through, but only one master LCON.

      The last screen of the dcct slot.port.vpi.vci command for the BPX 8600 platform presents different information:

      b4static       VT    StrataCom       BPX 8620  9.2.23    May  18 2000 1145 GMT 
      
      Slot 5   Port 0   VPI 0 VCI 99        LCON# 23  &31CD2CC2VC# 23  &3216D6DE
      
      Base XLT ptr  31133648 
      Xlat ptr      310C792C
      Cur,Nxt Indx  2, 0
      SEQ Number    10
      State         USED
      Trunk         7(5.3.255)  
      !--- in the BPX, this is the Slot.port.
      
      
      OE Trunk      255(5.3.255)
      Out Trk Chan  0
      This Chan     273  
      !--- in the BPX, this is the LCN.
      
      VPC(N) Conid  4351
      Master Node#  66
      Mstr LCon Idx 23
                                                                                   
      Last Command dcct 5.1.0.99
      
  2. Use the dspchstats slot.port.lcn command to view the connection status of an IGX 8400 trunk using the information collected from the dcct command.

    g4static       TN    StrataCom       IGX 8420  9.2.23    May  18 2000 1135 GMT 
    
    Trunk Channel Statistics 11.5 Lcn 262
    Collection Time 0 day(s) 000013                   Clrd  05/18/00 113533
    Type                                      Count     Traffic       Rate (cps) 
    Cells Received from Port                        1   From port              0
    Cells Transmitted to Network                    2   To network             0
    Cells Received from Network                     2   From network           0
    Cells Transmitted to Port                       2   To port                0
    EOF Cells Received from Port                    0
    Cells Received with CLP=1                       0
    Cells Received with CLP=0                       1
    Non-Compliant Cells Received                    0
    Average Rx VCq Depth in Cells                   0
    Average Tx Vcq Depth in Cells                   0
    Ingress Vsvd Allowed Cell Rate                  0
    Egress Vsvd Allowed Cell Rate                   0
    
    Cells Rx with CLP=0 from Network                2                           
    Cells Rx with CLP=1 from Network                0                           
    Cells TX with CLP=0 to Port                     2                           
    Cells TX with CLP=1 to Port                     0                           
    Non-Comp Cells Rx w/CLP=0 dropped               0
    Non-Comp Cells Rx w/CLP=1 dropped               0
    Overflow Cells Rx w/CLP=0 dropped               0
    Overflow Cells Rx w/CLP=1 dropped               0
    OAM state (0OK,1FERF,2AIS)                      0
    Good Pdu's Received by the Sar                  0
    Good Pdu's Transmitted by the Sar               0
    Rx pdu's discarded by the Sar                   0
    
    TX pdu's discarded by the Sar                   0                           
    Invalid CRC32 pdu rx by the sar                 0                           
    Invalid Length pdu rx by the sar                0                           
    Shrt-Lgth Fail detected by the sar              0                           
    Lng-Lgth Fail detected by the sar               0
                                                  
                                                 
    This Command dspchstats 11.5.262 1 
    !--- The 1 is for a one-second screen refresh rate.
    
    
  3. Use the dspchstats command to view the connection status of a BPX 8600 trunk using the information collected from the dcct command.

    b4static       VT    StrataCom       BPX 8620  9.2.23    May  18 2000 1146 GMT 
    
    Trk Channel Statistics for 5.3.273 Cleared May  18 2000 1146  (\)
    PCR 0/0 cps            Collection Time 0 day(s) 000017      Corrupted NO
       Traffic      Cells      CLP      Avg CPS   %util  Chan Stat Addr 30F69634
    From Port           0          0        0       0
    To Network          0      ---          0       0
    From Network        0          0        0       0
    To Port             0          0        0       0
                                                                                 
    
    Rx Frames Rcv          0  NonCmplnt Dscd         0  Rx Q Depth             0
    TX Q Depth             0  Rx CLP0                0  Rx Nw CLP0             0
    Igr VSVD ACR           0  Egr VSVD ACR           0  TX Clp0 Port           0
    Rx Clp0+1 Port         0  NCmp CLP0 Dscd         0  NCmp CLP1 Dscd         0
    Oflw CLP0 Dscd         0  Oflw CLP1 Dscd         0
                                                                                 
    This Command dspchstats 5.3.273 1 
    !--- The 1 is for a one-second screen refresh rate.
    
    

Via Node Discards Traffic Example

This section shows an example of a via node discarding traffic.

  1. Use the dspcon slot.port.vpi.vci command at the master end to determine the connection route through the network and examine the PVC segment at a via node. Then use these commands:

    • vt node_name — To connect to the next node in the connection path.

    • dnvc master_node_name master_Lcon_number — To collect the LCN information for each trunk card the connection traverses on the via node. The dnvc command is a service-level command whose output depends upon which switch type is used.

    network2       VT    StrataCom       IGX 8420  9.1.16    Dec. 13 1999  0135 G+01
    
    NW Lcon Ptr=317EA384, Vc Offset=0, MS Indx=175, SM Indx=177, GW=1
    
    TRUNK XLAT INFO (MS) 4 (15.1)       TRUNK XLAT INFO (SM) 2 (6.1)
    XLAT dB ptr      30ACF070             XLAT dB ptr      30ACF170 
    XLAT ptr         30AB4518             XLAT ptr         30ACC188 
    Cur Indx(d)      175                  Cur Indx(d)      177
    Nxt Indx(d)      0                    Nxt Indx(d)      0
    SEQ Number(d)    41                   SEQ Number(d)    41
    State,           U                    State,           U
    RCV,XMT dc(H)    10,10                RCV,XMT dc(H)    10,10
    RCV,XMT ch(H)    12,11                RCV,XMT ch(H)    11,12
    LCN(d)           175                  LCN(d)           177
    Master Node#     220                  Master Node#     220
    Mstr LCon Indx   1                    Mstr LCon Indx   1
    Mstr VC Indx     1                    Mstr VC Indx     1
                                                                                  
    Last Command: dnvc network1 1
    
  2. Use the dspchstats command to view the IGX connection status on a trunk using the information collected from the dnvc command.

    network2      VT    StrataCom       IGX 8430  9.1.16    Dec. 14 1999 2340 GMT 
    
    Trunk Channel Statistics 15.1 Lcn 175
    Collection Time 0 day(s) 000037                   Clrd  12/14/99 233956
    Type                                      Count     Traffic       Rate (cps) 
    Cells Received from Port                       40   From port              1
    Cells Transmitted to Network                    0   To network             0
    Cells Received from Network                    16   From network           0
    Cells Transmitted to Port                      16   To port                0
    EOF Cells Received from Port                    0
    Cells Received with CLP=1                       0
    Cells Received with CLP=0                      40
    Non-Compliant Cells Received                    0
    Average Rx VCq Depth in Cells                4093
    Average TX Vcq Depth in Cells                   3
    Cells Transmitted with EFCI=1                   0
    Cells Transmitted with EFCI=0                  16
                                                                                  
    This Command: dspchstats 15.1.175
    

    In this example, the dspchstats command isolated the problem to IGX 8400 switch network2 trunk 15.1. In this example, a UXM defect caused the transmit queue to fill and not play out cells. After the UXM transmit queue filled, subsequent traffic was discarded.

    Avoid using disruptive commands such as the resetcd slot_number h command, unless all network traffic has been routed from the offending trunk. Use the cnfpref connection_number command to restore data service by routing the connection around the offending trunk.

Related Information

Updated: Apr 17, 2009
Document ID: 7115