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Unable to configure both NM-16ESW switch modules on a 3600 or 3700 series router


Core Issue

With Cisco IOS  Software Release 12.2(11)T and later, two switch modules are supported in one 3600 or 3700 series chassis.

To support both modules, each module must have the Gigabit Ethernet (GE) module installed, and the modules must be connected through an external crossover cable.

Connecting the two GE interfaces, and issuing the stacking-partner command, eliminates conflicts in the VLAN databases between the two modules. Installing two modules without this connection results in duplications in the VLAN databases and is not supported.


If two switch modules are installed in the same chassis, ensure support by performing these steps:

  1. Verify that the Cisco IOS Software Release is 12.2(11)T or later and has a Plus feature set.

    To verify this, issue the show version command, as shown in this example:

    3725ESW#show version
    Cisco Internetwork Operating System Software
    IOS (tm) 3700 Software (C3725-IS-M), Version 12.2(11)T6,  RELEASE SOFTWARE (fc1)
    TAC Support:
    Copyright (c) 1986-2003 by Cisco Systems, Inc.
    Compiled Fri 14-Feb-03 18:50 by ccai
    Image text-base: 0x60008940, data-base: 0x617C4000
    ROM: System Bootstrap, Version 12.2(8r)T2, RELEASE SOFTWARE (fc1)
    3725ESW uptime is 2 weeks, 3 days, 23 hours, 34 minutes
    System returned to ROM by reload
    System image file is "flash:c3725-is-mz.122-11.T6.bin"
    Cisco 3725 (R7000) processor (revision 0.1) with 196608K/65536K bytes of memory.
    Processor board ID JMX0715L02P
    R7000 CPU at 240Mhz, Implementation 39, Rev 3.3, 256KB L2 Cache
    Bridging software.
    X.25 software, Version 3.0.0.
    SuperLAT software (copyright 1990 by Meridian Technology Corp).
    38 FastEthernet/IEEE 802.3 interface(s)
    DRAM configuration is 64 bits wide with parity disabled.
    55K bytes of non-volatile configuration memory.
    31744K bytes of ATA System CompactFlash (Read/Write)
    Configuration register is 0x2102

    This example shows that the Cisco IOS Software Release is 12.2(11)T6 in this line:

    IOS (tm) 3700 Software (C3725-IS-M), Version 12.2(11)T6,  RELEASE SOFTWARE (fc1)

    Because the letter S appears in the (C3725-IS-M) part of this line, the Cisco IOS Software running on the router has a Plus feature set. Therefore, two switch modules are supported.

  2. Verify that the switch modules have Gigabit modules installed.

    If you have physical access to the router, see if the Gigabit port is installed by looking at the lower left side of the switch modules. If no Gigabit port is installed, a cover plate should be in place.

    If you do not have physical access to the router, issue the show diag command. If a Gigabit card is installed, you should see command output similar to this:

    GigabitEthernet-0 daughtercard

            Hardware Revision        : 1.0

            PCB Serial Number        : JAD065209F0

            Part Number              : 73-6593-01

            Board Revision           : A0

            RMA Test History         : 00

            RMA Number               : 0-0-0-0

            RMA History              : 00

            Deviation Number         : 0-0

            Product Number           :

            Top Assy. Part Number    : 65535-16777215-255

            CLEI Code                : CNSPP20AAA

    For information on installing the Gigabit daughtercard, refer to Installing Gigabit Ethernet Boards in Cisco Ethernet Switch Network Modules.

      If the Cisco IOS Software is correct, and the Gigabit daughtercards are installed,  connect the Gigabit interfaces of the two modules with a crossover cable. Refer  to the Crossover  and Straight-Through Cable Pinouts section of Connector and Cable Specifications.

    The modules must be connected with the crossover cable to use both modules.

  3. Enable the modules to communicate by issuing the switchport stacking-partner interface [partner interface] interface configuration command. For example, if the two Gigabit interfaces are 2/0 and 4/0, the commands would appear as shown:
    router(config)#interface GigabitEthernet2/0
    router(config-if)#switchport stacking-partner interface GigabitEthernet4/0
    router(config)#interface GigabitEthernet4/0
    router(config-if)#switchport stacking-partner interface GigabitEthernet2/0
    router#show run
    interface GigabitEthernet2/0
      switchport mode trunk
      no IP address
     switchport stacking-partner interface GigabitEthernet4/0
     interface GigabitEthernet4/0
      switchport mode trunk
      no IP address
     switchport stacking-partner interface GigabitEthernet2/0
  4. The switch modules should now function properly.

When Problem Occurs

After hardware installation or replacement

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