I am replacing an old Catalyst 3550 (that has 2 Gig ports) with a 3750 (that has 4)- I used the exact same configuration in the new switch. When I plugged in the new 3750, the trunk ports started blinking from green to amber. I dont know why this is occuring- it SEEMS to be fine, but we havent thrown a whole bunch of traffic over it. But I realize there must be something incorrect- and I cannot find why this would be happening anywhere on google. Any suggestions?
Seems to be STP related. below is from 3750 Installation guide.
Amber :Port is blocked by Spanning Tree Protocol (STP) and is not forwarding data.
After a port is reconfigured, the port LED can remain amber
for up to 30 seconds as STP checks the switch for possible
Flashing amber :Port is blocked by STP and is transmitting or receiving packets.
On certain Catalyst switches, I have seen a port LED to alternate between green and amber rapidly when the port encountered a large number of errors, such as receiving 802.1Q tagged frames on an access port or similar. See the following document for a direct explanation of various port LED indications:
I recommend watching the console and logging output closely. If there are excessive errors detected by a port, the switch will log a message on the console and into other logging destnations (buffer, syslog). Also check the interface counters using the show interface and show interface counters errors commands. So far, we have no other indication as to what is the reason of your green/amber alternating LEDs.