Interconnecting 3Com switches with Cisco

Posted on 2012-08-28
Last Modified: 2012-09-07
Let's consider two 3com switches (4500 and 2924) and Cisco Catalyst 3750G.

1) How should interconnect 3com switches? Which ports should I use?
When I connect one of 25, 26, 27 or 28 port of 4500 to SFP port of 2924 I get an error: "fabric port is isolated because of connection error".

2) Which port of which switch should I connect to Cisco Catalyst 3750G?

See enclosed photo.
Question by:marianhe
    LVL 3

    Expert Comment

    You need to set the port to a trunk port which ever one you use. Have you ensured the ports are configured as trunks?

    Author Comment

    Your answer is applicable for which question?
    LVL 17

    Expert Comment

    Pick a port number:

    Configure Trunk on this port using:

    switchport trunk encap dot1q
    switchport mode trunk

    Assisted Solution

    No need to configure trunk.
    I do not want Cisco VLANs in 3com switches.

    To interconnect 3com Baseline 2924 and Cisco 3750G, you just need to use one of 3com SFP ports. It works.

    Author Comment

    Still first question remains not answered.
    LVL 3

    Expert Comment

    You can use which ever SFP port you want as long as you configure it as a trunk port with the same configuration on both switches for interconnecting ports. If you just plug in the cable it is likely the port is configured as an access port with extra configuration expecting a pc/phone or other access device to be plugged in. This causes issues with connectivity between switches.

    Trunk has no relation to VLAN. dot1q does and you do not need to configure this unless you want VLANs across your network to pass through the port.

    If you have no VALns then this is not applicable but you still need theport to be a trunk port.

    If you do run VLANs and you do not enable dot1q then the vlans will not pass through the port.

    Author Comment

    [4500-GigabitEthernet1/0/27]display interface GigabitEthernet 1/0/27
     GigabitEthernet1/0/27 current state : DOWN
     IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 0016-e023-4b7b
     The Maximum Transmit Unit is 1500
     Media type is twisted pair, loopback not set
     Port hardware type is 1000_BASE_T
     Unknown-speed mode, unknown-duplex mode
     Link speed type is autonegotiation, link duplex type is autonegotiation
     Flow-control is not enabled
     The Maximum Frame Length is 1522
     Broadcast MAX-ratio: 100%
     Unicast MAX-ratio: 100%
     Multicast MAX-ratio: 100%
     PVID: 1
     Priority: trust
     Mdi type: auto
     Port link-type: xrn-fabic
      Tagged   VLAN ID : all
      Untagged VLAN ID : none
     Last 300 seconds input:  0 packets/sec 0 bytes/sec
     Last 300 seconds output:  0 packets/sec 10 bytes/sec
     Input(total):  67 packets, 12480 bytes
    	 22 broadcasts, 34 multicasts
     Input(normal):  - packets, - bytes
    	 - broadcasts, - multicasts
     Input:  11 input errors, 11 runts, 0 giants,  - throttles, 0 CRC
    	 0 frame,  - overruns, 0 aborts, 0 ignored, - parity errors
     Output(total): 47 packets, 7032 bytes
    	 0 broadcasts, 47 multicasts, 0 pauses
     Output(normal): - packets, - bytes
    	 - broadcasts, - multicasts, - pauses
     Output: 0 output errors,  - underruns, - buffer failures
    	 0 aborts, 0 deferred, 0 collisions, 0 late collisions
    	 0 lost carrier, - no carrier
    [4500-GigabitEthernet1/0/27]port ?
      access            Specify current access port's characteristics
      hybrid            Specify current hybrid port's characteristics
      isolate           Port isolate
      link-aggregation  Link aggregation group
      link-type         Specify port link-type
      trunk             Specify current trunk port's characteristics
    [4500-GigabitEthernet1/0/27]port  link-type ?
      access      Access link-type
      hybrid      Hybrid VLAN link-type
      trunk       VLAN trunk link-type
      xrn-fabric  Fabric-port link-type
    [4500-GigabitEthernet1/0/27]port  link-type trunk ?
    [4500-GigabitEthernet1/0/27]port  link-type trunk 
     Can not configure fabric port!

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    LVL 3

    Expert Comment

    From what I understand to configure the port to a trunk port if it is configured as a fabric port you need to first configure as an access port and then configure to be a trunk port.

    Can you try using the command:

    undo port link-type

    then do port

    link-type trunk

    A fabric port is used for stacking.

    You may also need a cross over cable if you are using Ethernet to link the 2 switches together.

    Accepted Solution

    Only link-type access is needed. No trunk.
    LVL 3

    Expert Comment

    Although link-type access will work you will find later down the line you have the inter-connecting ports shutting down because of illigal traffic. This will be because of mis-configuration of port type where you have set the uplink ports to access and not trunk.

    Author Closing Comment

    My solutions are the best.

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