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DELL N3048EP-ON/Cisco C2960S etc. STP issues access ports configured as Trunks
Good Afternoon,
LAN with 10 switches, top of rack, DELL N3048EP-ON & Cisco C2960S, 6 x C2960+ & 2 x N2048P
Access ports configured as trunk ports due to need for 3 VLAN per port, 1 Data and 2 Voice during an IP phones transition.
STP flooding message issues being recorded on the DELL N3048EP-ON from multiple Cisco switches, performance between switches seriously impaired.
below messages on the N3048EP-ON, from the C2960S, where the C2960+'s are connected
<189> Nov 26 08:55:21 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36647 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 4 Gi1/0/1
<189> Nov 26 08:55:21 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36646 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 3 Gi1/0/1
<189> Nov 26 08:55:20 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36645 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 2 Gi1/0/1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36644 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 4 Gi1/0/1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36643 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 3 Gi1/0/1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36642 %% NOTE Spanning Tree Topology Change: VLAN 4, Unit: 1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36641 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 4 Gi1/0/1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36640 %% NOTE Spanning Tree Topology Change: VLAN 3, Unit: 1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36639 %% NOTE Spanning Tree Topology Change Received: VLAN ID: 3 Gi1/0/1
<189> Nov 26 08:55:19 SW02-1 TRAPMGR[dot1s_task]: traputil.c(763) 36638 %% NOTE Spanning Tree Topology Change: VLAN 2, Unit: 1
Any idea's?
Many thanks
Richard
DELL-Tim G
3 Apprentice
3 Apprentice
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73 Posts
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December 1st, 2020 06:00
Hello Richard,
the N3048EP is receiving STP Topology Change Notifications (TCNs) for each VLAN from the link to the Cisco switch.
That means your Cisco switches are seeing topology changes (link up/down) on any port participating in the corresponding VLAN and are flooding them to all other bridges.
Cisco normally uses rapid per VLAN STP (RPVST) per default which builds a separate spanning tree for each VLAN - hence a TCN per VLAN as opposed to RSTP which builds only a common instance (default on our N-Series switches).
Longs story short - look for unstable connections in your Cisco network segment,
shut them down to stop the TCNs as they are forcing each receiving switch to clear and re-learn their MAC tables for the corresponding VLAN.
If this happens with high frequency it can impact network performance.
If you see access ports flapping you might think about using the STP "port-fast" or "edge-port" option which does suppress the generation of a TCN after link state change.
A network in a converged and stable state should normally not see any TCNs.
Tim