I have a Brocade ICX 7450-48F switch that is being used as my Distribution Switch for my small network. It has a single 1G connection to a Cisco 3560 via single mode fiber.
The ICX is configured with Port-name Dual-mode X
The Cisco device is configured with trunk encapsulation dot1q switchport trunk native vlan (X to match the ICX) switchport trunk allowed vlan 1 - X switchport mode trunk switchport nonegotiate mls and qos configurations
The Issue: The ICX connection to the Cisco device is flapping, meaning I am losing connection to the downstream Cisco device. A Show Log reveals that interface e 1/1/3 is receiving STP State messages for each of my configured VLANS, meaning that each VLAN in the log is cycling through its Listen Learn Forward State
for example :
VLAN X Port 1/1/3 STP State -> Listening (MakeFwding) VLAN X Port 1/1/3 STP State -> Learning (FwDlyExpiry) VLAN X Port 1/1/3 STP State -> Forwarding (FwDlyExpiry)
I don't understand why STP/BPDU is frequently updating itself causing the interface to bounce. Could this be avoided if I add a second 1G trunk between the ICX and Cisco device? We are not seeing any input or output errors on either side of the link so I didn't want to jump to the possibility that the fiber is dirty.
We will get STP flaps when there are topology changes, If you look at output of "show span detail" do you see lots of TCNs on any particular port? If so we need to focus on it. Check for errors on that port which has lot of TCN received on, Or try to find any other reasons why we see transitions, for example port flapping. Also check the ports are configured correctly for PC ports vis a vis switch ports. If a PC port is bouncing it can cause a lot of Topology change if we do not configure it with admin-edge-port on the port context, vs admin-pt2pt-mac for a port connecting to another switch.