What types of loops would you imagine in general? loops maybe of many levels: L1, L2, L3, at processes level, mental, intellectual, etc.

• L1: frequency synchronisation in DWDM is a good example of such loops if lower stratum number get updates from higher stratum in some way. No way to troubleshoot…
• L2: STP spanning tree protocol in LAN network, (ieee 802.3d, rstp, pvst, pvst+, mstp, etc.), if there are redundant physical links and no stp is active or buggy… another way to prevent from such loops: TRILL, fabric path, ring vendor topologies (such as Extreme Network ESRP protocol), etc.
• L3: routing, bad routing decition that breaks routing per definition or its performance…
• Process: with regards to some task, working but able to move forward or get new results, building and destructing continually, etc.