EOS Switches have spanning tree enabled by default and EXOS switches do not, making it important to use care when connecting them together to avoid data loops in the network.
EOS switches are configured with MSTP by default and use there MAC address as part of the configuration digest. Unless the config digest on two or more switches are configured the same the switches will be in different regions and behave like a Rapid Spanning Tree 802.1W link.
If you configure an EXOS switch to use Rapid Spanning Tree it will require the configuration of an untagged VLAN to other switches to carry BPDU's. Avoid having to configure the untagged VLAN by Configuring MSTP on the EXOS switch.