MPLS over GUE (Generic UDP Encapsulation) is a tunneling mechanism for encapsulating MPLS IP traffic in a UDP header. This feature adds support for MPLS over GUE encapsulation for BGP VPN routes resolving over IPv4 next hops. 

BGP VPN routes today advertise a label by dynamically allocating it from a dynamic label range block without providing the user any control over the label value that is allocated per VRF’s address Family - VPNv4 or VPNv6. This feature allows the user to configure a unique label per VRF’s configured address-family, VPNv4 or VPNv6, thereby allowing the user granular control over the label value advertised with VPN routes exported from a VRF.

In a symmetric network topology, for the same ECMP (Equal Cost Multi Path) route programmed at different devices in a switch layer, the various devices can program ECMP next hops in the FEC (Forwarding Equivalence Class) for that route in varying orders.

Accumulated IGP Metric (AIGP) is an optional non-transitive BGP attribute used to carry an IGP metric with BGP route advertisements. The AIGP attribute is useful for tie-breaking in BGP bestpath selection so that routing decisions can be made on the basis of shortest path/lowest IGP cost path amongst multiple BGP paths. This is particularly applicable in scenarios where a single administration is subdivided into multiple Autonomous Systems (AS) each with similar routing policies and the same IGP in use such that the IGP metric for a route can be propagated usefully between the ASes so as to let receiving BGP speakers make routing decisions based on the cumulative IGP cost of the route. This set of ASes in a common administrative domain in the context of advertising and receiving the AIGP attribute are referred to as an AIGP administrative domain.