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Thursday, February 9, 2012

Cannot Uplink/Daisy Chain Cisco 2960 S Series Switch to Cisco 3750 Switch


We have a new Cisco 2960 S series switch with a basic configuration that needs to be uplinked or daisy chained to a Cisco 3750 switch. We are not getting any connectivity to the network with either a straight through or crossover cable. the port remains in amber but a 'show interface' indicates that the interface is up. We can manage the switch with a PC patched into any port on the switch with a static IP address.

Amber could mean a few things:

1. Spanning-tree;
2. Auto-negotiation between access and trunk port.

If you'd like try the following command on each switches:

2960S
interface
switchport mode trunk
speed auto
duplex auto

3750
default interface
interface
switchport encapsulation dot
switchport mode trunk
speed auto
duplex auto

If the spanning tree put the port in blocking mode for a reason , somewhere you have a built in loop in your design and you could put your net at risk by shutting off spanning tree between devices.


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