MCT Layer 2 Protocols

Keep the following information in mind when configuring Layer 2 protocols with MCT:

• Metro Ring Protocol (MRP)—An ICL interface cannot be configured as an MRP secondary interface or vice versa because the ICL cannot be in a blocking state.

  MRP cannot be enabled on an MCT CCEP or vice versa.

• Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP)—RUCKUS does not recommend configuring STP on MCT VLANs at MCT cluster devices. By, default, the spanning tree is disabled in the MCT VLANs.

  If the network topology creates Layer 2 loops through external connections of MCT clients, STP or RSTP may be enabled on MCT clients to prevent the Layer 2 loops. The MCT cluster devices then perform a pass-through forwarding of STP BPDUs received through its ports in the MCT VLAN. Refer to MCT client configuration examples using STP to view deployment scenarios where STP is used on MCT clients to prevent Layer 2 loops.

  The MCT cluster devices do not perform pass-through forwarding of untagged STP BPDUs received through its ports in the MCT VLAN. Single STP and IEEE 802.1s (MSTP) are not useful on MCT clients to prevent the Layer 2 loops.

  If the network topology creates Layer 2 loops through CEPs, STP or RSTP may be enabled on MCT cluster devices to prevent the Layer 2 loops. But MCT cluster devices are treated as two separate bridges when STP or RSTP is enabled on MCT VLANs. It is not recommended to enable STP or RSTP on the MCT VLANs of cluster devices. Refer to STP configuration example on MCT cluster devices to view deployment scenarios where STP is used on MCT cluster devices to prevent Layer 2 loops.

  • The STP or RSTP algorithms have been modified so that the ICL never enters a blocking state. The ICL guard mechanism ensures that if the ICL is about to go into a blocking state, the port on which the superior BPDUs are being received is moved to a blocking state, and the ICL guard timer starts running on it. This timer runs as long as superior BPDUs are received on this interface. As long as this timer runs on an interface, the superior BPDUs are dropped.
  • The BLK_BY_ICL STP state indicates that superior BPDUs were received on this interface, which could have led to blocking of the ICL interface, with the result that the CL port guard mechanism has been triggered on this port.
  • In an 802.1s MSTP deployment, RUCKUS recommends disabling spanning tree on MCT cluster devices at the global level. MSTP cannot be configured on individual cluster devices.
  • Configuring STP/RSTP on MCT VLANs in the cluster devices and enabling STP/RSTP at MCT clients for a pass-through forwarding of STP/RSTP BPDUs received at CCEP ports will not work.
  • An MCT cluster can support up to 32 spanning tree instances.