Implement and Troubleshoot Loop Prevention Mechanisms
Loops can occur when you are redistributing bidirectionally at 2 different points in the network
Route Tagging, Filtering
Route tagging is the process of adding an indentifier (tag) to a set of prefixes. This tag can then be called in a route map. The way I map out how to filter routes is pictured below
Split Horizon
Split horizon is used by distance vector routing protocols. This prevents a router from sending a route back out an interface that the route was learned from. The only time you would disable this is in a hub/spoke setup where the hub would need to send routes learned back to other spokes.
Route Poisoning
Used by distance vector routing protocols. Once you learn of a route through an interface, advertise it as unreachable back through that same interface
