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RSTP Interoperation Between Huawei's NE40Es and Foundary's Switches Failed Due to Incorrect Configurations on NE40Es

Publication Date:  2013-09-27 Views:  36 Downloads:  0
Issue Description
In the network shown in the following figure, Foundary's switches 17, 18, 19 and Huawei's NE40E-X2s A, B, and C were enabled with Rapid Spanning Tree Protocol (RSTP). RSTP interoperation between the switches and NE40Es failed. Two root bridges were elected.

Handling Process

Huawei completed the following steps to diagnose the problem:
1. Captured packets. The BPDU packets sent by the switches carried VLAN tags. (Do not perform this check on a PC running the Windows OS, which automatically deletes VLAN tags from packets.)

2. Queried traffic statistics and debug information on the switches. The BPDU packets from NE40Es were discarded. The RSTP topology on the NE40Es was not stable and all ports received/transmitted BPDU packets.
3. Checked for the specific STP type used on the switches. Although RSTP was enabled on the configuration interface, the effective STP on the switches was Cisco's proprietary Per-VLAN Spanning Tree (PVST).
4. Checked the differences between RSTP implementation and PVST implementation. On PVST-enabled switches, a separate protocol packet is sent and a spanning tree instance is maintained for each VLAN. RSTP-enabled NE40Es do not support multiple VLANs, and therefore cannot send protocol packets or maintain spanning tree instances on a per-VLAN basis.
5. Enabled PVST globally and configured multi-process RSTP on the NE40Es. One root bridge was elected.

Root Cause
PVST, not RSTP, was effective on Foundary's switches.

1. Enable PVST globally.

stp bpdu-encapsulation pvst


2. Enable multi-process RSTP on the NE40Es.
stp process 1
 stp mode rstp
 stp enable
 stp converge fast
stp process 2
 stp mode rstp
 stp enable

3. Associate VLANs with RSTP processes for interfaces.
interface GigabitEthernet7/0/0  portswitch
 undo shutdown
 stp binding process 1 serve-vlan 32 bpdu-vlan 32
 stp binding process 2 serve-vlan 2601 bpdu-vlan 2601

When an interoperation problem occurs, the packet capturing method is helpful.