This blog is related to Nortel and Cisco switch spanning tree interoperability problems which I was faced on my site.
Network Setup:
We are having a Nortel 8606 at core of our network and Cisco 2960 at access layer. Access layer switches are directly connected with core. The Cisco switch and Nortel core switch are managed by using the VLAN 1 IP address. There was 8 VLAN’s at our core 8606 Switch. And the same 8 VLAN’s are created on Cisco 2960 also.
Problem:
One day we have tried to delete VLAN 8 because it was not applied to any of the PC in our network. But we have found the IP address of the Cisco switches was not reachable. The same IP was reachable after creating the VLAN 8. We have received a log on Cisco switch stating that the switch has received an inconsistent BPDU on VLAN .so the switch blocks the VLAN 1.
Solution:
The problem was due to Spanning tree protocol.
Actually the Nortel core 8606 was configured with Nortel STG (Nortel Proprietary protocol) and Cisco 2960 was running with PVST+ (Cisco Proprietary protocol).In Nortel STG all the 8 VLANs are grouped and only one BPDUs are sent. But in PVST+ each VLAN will have different STP instance and each VLAN will sent different BPDUs.
In Nortel even it receives the 8 different BPDUs from different VLANs it will only process for the VLAN 1 Bpdu and the remaining VLAN Bpdus are not processed and it is forwarded as it is to the another Cisco switch. When the VLAN 8 was deleted on the Nortel 8606 Core switch the core switch has received the VLAN 8 Bpdu's from one Cisco device and sent it to another cisco device via VLAN 1(Because the VLAN 8 is not existing on the Nortel switch).when the another Cisco devices receives the VLAN 8 BPDU via VLAN 1 it considers that there is a fault in the network due to that only it is receiving VLAN 8 BPDU on VLAN 1.and it start changing the port to VLAN inconsistency state for VLAN 1.
How to Avoid:
To avoid this type of problems delete the VLAN on all the Cisco devices first and then delete it on Nortel. So the BPDUs will not be generated on Cisco.
Network Setup:
We are having a Nortel 8606 at core of our network and Cisco 2960 at access layer. Access layer switches are directly connected with core. The Cisco switch and Nortel core switch are managed by using the VLAN 1 IP address. There was 8 VLAN’s at our core 8606 Switch. And the same 8 VLAN’s are created on Cisco 2960 also.
Problem:
One day we have tried to delete VLAN 8 because it was not applied to any of the PC in our network. But we have found the IP address of the Cisco switches was not reachable. The same IP was reachable after creating the VLAN 8. We have received a log on Cisco switch stating that the switch has received an inconsistent BPDU on VLAN .so the switch blocks the VLAN 1.
Solution:
The problem was due to Spanning tree protocol.
Actually the Nortel core 8606 was configured with Nortel STG (Nortel Proprietary protocol) and Cisco 2960 was running with PVST+ (Cisco Proprietary protocol).In Nortel STG all the 8 VLANs are grouped and only one BPDUs are sent. But in PVST+ each VLAN will have different STP instance and each VLAN will sent different BPDUs.
In Nortel even it receives the 8 different BPDUs from different VLANs it will only process for the VLAN 1 Bpdu and the remaining VLAN Bpdus are not processed and it is forwarded as it is to the another Cisco switch. When the VLAN 8 was deleted on the Nortel 8606 Core switch the core switch has received the VLAN 8 Bpdu's from one Cisco device and sent it to another cisco device via VLAN 1(Because the VLAN 8 is not existing on the Nortel switch).when the another Cisco devices receives the VLAN 8 BPDU via VLAN 1 it considers that there is a fault in the network due to that only it is receiving VLAN 8 BPDU on VLAN 1.and it start changing the port to VLAN inconsistency state for VLAN 1.
How to Avoid:
To avoid this type of problems delete the VLAN on all the Cisco devices first and then delete it on Nortel. So the BPDUs will not be generated on Cisco.
