Interoperability issues between MST and legacy protocols of HP and old 3Com switch

Published by Andrea on

PTX_3355A friend of mine asked me help to solve a problem with the installation of a new HP 5406R switch within his corporate network.

Connected to the existing 3Com Switch 4200G with a gigabit cable, everything worked properly, connected with a 10 Gbit cable, the switch was isolated from the network.

The problem was an incompatibility between the Multiple Spanning Tree of the two systems, when the 5406R tried to elevate itself to be root, the 4200G blocked the 10Gbit port and log the error “-Instance0’s INCOMPLIANCE-Protection port tengigabitethernet1/0/1 receive incompliant message!”, this is due to native mode 802.1s of the HP switch, set in legacy mode, with the spanning-tree legacy-mode command, everything works and the HP switch has become the root of the instance 0 in the MST region.


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