Hello Manami
Regular BGP supports IPv4 unicast prefixes. MP-BGP is multi-protocol BGP, and it is an implementation of BGP that supports multiple protocols such as IPv4 unicast, IPv4 multicast, IPv6 unicast, and IPv6 multicast.
It is also used extensively with MPLS VPN in order to be able to share information from VRFs and VPNv4 routes. MP-BGP in simple terms includes fields in the BGP header where info about these things (VRFs, VPNv4 routes etc) can be shared, enabling MPLS VPN implementations.
More info about this can be found here:
Implicit null occurs by default. This is a situation where the penultimate router pops the label and sends the plain IP packet to the last hop router. Explicit null if configured, will not have the penultimate router pop the label, but sends a label value of 0 and keeps other fields intact. This allows the other fields that may contain QoS information, to be processed as well. More info about these concepts can be found at the following Cisco link:
You can also get some more info about this from the following post by Rene:
I’m not sure what you mean exactly. Do you mean if these protocols don’t converge? If an IGP doesn’t converge, then there is a problem in the topology or the configuration, and routing will not function correctly. Similarly, if LDP doesn’t exchange label information correctly, incorrect routing will take place.
I hope this has been helpful!
Laz