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

AS-PATH is a BGP-specific attribute used to prevent loops within BGP autonomous systems and does not apply to general multiprotocol redistribution between IGP domains.

Route tags are values attached to routes during redistribution that can be matched and filtered at other redistribution boundaries. By tagging routes as they enter a domain and denying those tagged routes at other redistribution points, a router identifies and discards routes that have already traversed a specific domain. This mechanism directly breaks the feedback cycle that causes redistribution loops in multi-domain topologies.

Split horizon prevents a route learned on an interface from being advertised back out that same interface, which applies to distance-vector updates on individual links, not to inter-domain redistribution loops.

Spanning Tree Protocol operates at Layer 2 to prevent Ethernet bridging loops and has no function in Layer 3 routing domain redistribution.