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2960 and network on unmanaged switches

Unanswered Question
Nov 18th, 2010
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We've got network build on unmanaged switches. Network size is about 170 computers.

Sometime ago we expanded our office with a few rooms. So as to connect these rooms to our network we bought catalyst 2960 (C2960-48TT-L if it is important), because we are thinking about migrate whole network to managed switches and VLANs and this C2960 should be first step

But after unpacking and connecting C2960 to our unmanaged switch we've got problem: link between C2960 and unmanaged switch not work.

Computers connected to C2960 see only C2960's network, but not computers connected to unmanaged switches. Computers, connected to unmanaged switches, see only unmanaged network, but not coumputers connected to C2960.

C2960 is in default config. I'd configured only IP address and telnet access from Express Setup. All computers are in one IP subnet. Physical link is ok - LanTester shows no problems and if I replace C2960 with unmanaged switch network works fine.

LED on port which connected to unmanaged switch is amber. In web-interface this port shows: "port is disabled". I'd tried to connect link to another free port on C2960 - result is the same.

How to get link between C2960 an unmanaged switch work?

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Peter Paluch Thu, 11/18/2010 - 10:11
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Do you have any redundant connections in your network? Is there any possible Layer1 (physical) loop? Are there any log messages appearing on the 2960?

In any case, if a port on the 2960 switch is amber then it means it is blocked for some purpose. Because of STP, the port will obviously be blocked for 30 seconds after its connection. But after 30 seconds, if there are no loops in the network, the port should become green and start functioning properly.

Please try to post the output of the following commands:

  • show spanning-tree
  • show interfaces status
  • show interface XXX switchport ! select an interface towards an unmanaged switch
  • show interface XXX ! select an interface towards an unmanaged switch
  • show cdp neighbor

Best regards,


Sebastian Helmer Thu, 11/18/2010 - 10:21
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I would say the default setting should work. Vlan 1 will be used and the port negotation could work.

please post a sh interfaces "gig / fast" 0/x switchport from the interface you connect the unmanged switch.

or sh run interface "fas/gig" 0/x

How long did you wait? Amber could be a spanning-tree in default no portfast in enable and the port need a time "30sec" to become green.




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