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.