A study on community-triggered updates in BGP

[Thomas Krenc]

Dear BIRD users and developers,

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 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).

    Is this side-effect known to the BIRD community and would you
consider it a bug or a feature?

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