Dear NANOG, As a team of researchers from NPS and TU Berlin, we are investigating the impact of BGP community attributes on the update behavior between ASes. We find that when a route is associated with multiple distinct community attributes it does not only lead to multiple announcement at the tagging AS, but also at neighboring ASes, if communities are not filtered properly. This behavior is wide-spread. In order to better understand our observations, we have performed a series of laboratory experiments using Cisco IOS, Junos OS, as well as the BIRD daemon. We find that - by default - all tested routers generate announcements with changing community attributes, even when other attributes do not change. In addition, when communities are filtered at egress, Cisco und BIRD send duplicate announcements (Juniper does not). Since our findings are limited to observations in public data as well as few router implementations, we would like to share our research and kindly ask you to have a look at:     https://www.cmand.org/communityexploration/ There, we provide some resources documenting our research, as well as open questions. We greatly appreciate any feedback and insights you can offer. Also, please don't hesitate to contact us directly:     communityexploration AT cmand DOT org best regards Thomas Krenc Postdoctoral Researcher Naval Postgraduate School