A study on community-triggered updates in BGP


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:


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