Spanning Tree
Ethernet network design balances two separate imperatives. First, Ethernet
has no capacity for detecting circular paths. If such paths exist, traffic loops
around and accumulates until new traffic is shut out (this is called a broadcast
storm). Second, having secondary paths is good preparation for
inevitable link failure.
Spanning Tree is a protocol that prevents loop formation by detecting redundant
links and disabling them until needed. Designers can therefore build
redundant links and the protocol will allow one to pass traffic and keep the
other in reserve. When the active link fails, the secondary link is enabled
quickly.