I'm fairly new with the cisco switches and this is my question. How do I find an uplink from a 3550 to our cores which are 6509 with 720 engines.
Perhaps someone else can provide detailed procedures, especially specific to the 3550, but some approaches I've used are:
On Cisco equipment, if CDP is active, and supported, showing CDP information often reveals the interface the other device is connected on.
Or, if possible, ping the other uplink device then determine the device's MAC (from ARP table) and then look to see if there a table of MACs per interface.
Or, look for VLANs (especially trunks) or subnets that match those seen on the uplink device. (Seeing both devices configs, can be necessary because one could actually have different uplink connections even to the same other device. I.e. The first two approaches might not reveal the other uplinks, and can be blocked.)