Distance vector protocols (like RIP) are prone to routing loops. Several mechanisms prevent them:
- Split horizon: Don't advertise a route back to its source
- Route poisoning: Advertise failed routes with infinite metric
- Poison reverse: Return poisoned routes with infinite metric
- Hold-down timers: Ignore updates about failed routes temporarily
- Triggered updates: Send updates immediately on topology changes
Link-state protocols avoid loops by design since each router calculates paths independently.