We propose a methodology to match detailed BGP updates from two neighboring Autonomous Systems (ASes). This methodology allows us to characterize route propagation and measure the route propagation time. We apply this methodology to two months of all BGP updates from Abilene and GEANT to perform the first thorough characterization of BGP route propagation between two neighbor ASes. Our results show that the propagation time of BGP routing changes is very different depending on the network that initiates the routing change. This difference is due to engineering and connectivity issues such as the number of prefixes per BGP session, the number of BGP sessions per router, and BGP timer configurations.