In an MPLS PE router, CE advertised routes are segmented from other CE routers by assigning CE-facing interfaces to different Virtual Routing and Forwarding (VRF) instances12. A VRF is a technology that allows multiple instances of a routing table to co-exist within the same router at the same time. By associating a network interface with a VRF, the network layer (Layer 3) has a different view of the network topology. This allows the segmentation of routing paths for traffic from different customers or different types of traffic. In the context of MPLS, VRFs are used to create separate routing instances for each customer on a PE router3.
References:
Implementing Cisco Enterprise Advanced Routing and Services (ENARSI) training videos CCNP Enterprise Advanced Routing ENARSI 300-410 Official Cert Guide Implementing Cisco Enterprise Advanced Routing and Services source documents or study guide MPLS routes to advertise from CE to PE - Cisco Community Configuring Route Exchange Between PE and CE Devices - CloudEngine 12800 and 12800E V200R005C10 Configuration Guide - VPN - Huawei Customer edge router - Wikipedia

After redistribution, R3 learns about network 10.1.1.0/24 via two paths:+ Internal BGP (IBGP): advertised from R4 with AD of 200 (and metric of 0)+ OSPF: advertised from R1 with AD of 110 (O E2) (and metric of
20)Therefore R3 will choose the path with the lower AD via OSPF
But this is a looped path which is received from R3 -> R2 -> R1 -> R3. So when the advertised route from R4 is expired, the looped path is also expired soon and R3 willreinstall the main path from R4. This is the cause of intermittent connectivity.In order to solve this issue, we can lower the AD of iBGP to a value which is lower than 110 so that it is preferred over OSPF-advertised route.