When a multiprotocol routing environment is designed to have several routers redistributing among the routing domains, how can routing loops be avoided?

Spanning Tree Protocol operates at Layer 2 to prevent Ethernet switching loops and has no relevance to Layer 3 routing loops introduced by redistribution between routing protocols.

Split horizon prevents loops within a single distance-vector routing domain by not advertising a route back out the interface it was learned on; it does not function across different routing protocol boundaries where redistribution occurs.

The AS-path attribute is a BGP-specific loop prevention mechanism that only applies to BGP peering sessions and is unavailable in generic multiprotocol redistribution scenarios involving OSPF, EIGRP, or other IGPs.

Route tags allow administrators to stamp a numeric tag on routes as they enter a domain through redistribution; distribute-lists or route-maps on the receiving side can then filter out any route carrying that tag, preventing it from being redistributed back into its origin domain and breaking the loop.