Ethernet frames may be broadcast through the network with a header that does not contain a TTL. If the topology contains a loop, this leads to a broadcast storm with frames being broadcast indefinitely. The IEEE 802.1D Spanning Tree Protocol (STP) prevents bridge loops and the broadcast storms that result from them by disabling links and leaving a single active path between two network nodes. STP also facilitates a redundant link that is automatically instantiated in the event a primary link fails. STP variants include Rapid Spanning Tree Protocol (RSTP) for rapid convergence and Multiple Spanning Tree Protocol (MSTP) that enables load-balancing across different groups of VLANs.