If you configure the redistribution of OSPF into BGP without keywords, only OSPF intra-area and inter-area routes are redistributed into BGP, by default. You can use the internal keyword along with the redistribute command under router bgp to redistribute OSPF intra- and inter-area routes.
Use the external keyword along with the redistribute command under router bgp to redistribute OSPF external routes into BGP.
-> In order to redistribute all OSPF routes into BGP, we must use both internal and external keywords. The full command would be (suppose we are using OSPF 1):
redistribute ospf 1 match internal external
Note: The configuration shows match internal external 1 external 2. This is normal because OSPF automatically appends "external 1 external 2" in the configuration. In other words, keyword external = external 1 external 2. External 1 = O E1 and External 2 = O E2.
Reference:
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5242-bgp-ospf-redi s.html

MPLS Layer-3 VPNs provide IP connectivity among CE sites * MPLS VPNs enable full-mesh, hub-andspoke, and hybrid IP connectivity * CE sites connect to the MPLS network via IP peering across PE-CE links * MPLS Layer-3 VPNs are implemented via VRFs on PE edge nodes * VRFs providing customer routing and forwarding segmentation * BGP used for signaling customer VPN (VPNv4) routes between PE nodes * To ensure traffic separation, customer traffic is encapsulated in an additional VPN label when forwarded in MPLS network * Key applications are layer-3 business VPN services, enterprise network segmentation, and segmented layer-3 Data Center access

Reference:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/15-s/mp-l3-vpns-15-s-book/mp-bgp-mpls-vpn.pdf