Showing results for 
Search instead for 
Did you mean: 


Introducing the next generation of Cisco Small and Medium Business Switches. Cisco is refreshing its SMB Switch portfolio. Click here  to learn more.


Problems with fiber connection between 3Com 5500G-EI and Cisco SG-300-52

We’ve just begun the transition from our old 3Com switches to new Cisco switches and we’ve encountered interoperability problems as we start the transition.

Goal:  Extend 6 VLANs (each representing an IP subnet) via fiber from a port on the 3Com 5500G-EI to a port on the Cisco SG-300-52

  • •1)      We assign an IPV4 address to the Cisco SG-300-52.  We can successfully ping/web-manage at this address if we do a temporary copper jumper from a 3Com switch to the Cisco.  IP address is in the subnet assigned to VLAN7
  • •2)      At the 3Com side, the fiber port is set as “hybrid” and is passing VLAN 1 untagged; VLANs 3-8 tagged
  • •3)      At the Cisco side, the fiber port is set as “trunk” and is defined with VLAN 1 untagged and VLANs 3-8 tagged.

  • •A)     If I try to change the management interface on the CISCO from VLAN 1 to VLAN 7 (as I would on the 3Com), I lose connectivity over the temporary copper connection
  • •B)      If I remove the temporary copper jumper from the Cisco (keeping the “working” management IP address) and create the fiber link between the 2 switches, I lose connectivity to the management IP

Additional information:

  • •-          If I set the 3Com fiber port to “access” and make the fiber connection, I can ping the management interface – but of course, I can’t pass the other VLANs to untagged access ports on the Cisco – and it has the fun side benefit of messing with IP management settings on other 3Com switch stacks attached to the 5500G-EI.  However, it does demonstrate that we can get network traffic communicating over the fiber link between the 2 switches

Does anyone have any suggestions as to how I can proceed to a) have the management IP address in the IP subnet defined on VLAN 7 while passing the other VLANs to access ports on the Cisco?  BTW, I’m a networking neophyte (it’s a very small part of my job and I do it infrequently), so I prefer to use GUI management to CLI options, although I can perform CLI configuration if presented with the right commands.

Thanks in advance for any suggestions.  I’ve got a major summer project on hold until this is completed (I’ve got 3 of the Cisco SG-300s that need to be configured and attached to the central 3Com fiber switch).

Everyone's tags (4)

Problems with fiber connection between 3Com 5500G-EI and Cisco S

Hello Raymond,

The switch has a management VLAN configuration option. You may achieve setting the VLAN 7 as the management VLAN on the IPv4 Interface

Administration > Management Interface > IPv4 Interface

Ensure that when you change the management VLAN to a different VLAN that you associate a port to the VLAN 7 as 7untagged, otherwise you will no longer have access to the switch.


-Tom Please mark answered for helpful posts