When I run tcpdump on one of the KNI interfaces used by Gatekeeper, it immediately brings down BGP sessions running on the respective interfaces (the connection state in Bird changes to "Neighbor lost").

There are no correlated errors that I could find. ifconfig and ethtool outputs don't change during the tcpdump execution. There are no Gatekeeper logs, and the only kernel messages are the ones indicating the interfaces entered or left promiscuous mode.

Once tcpdump is stopped, the session is restablished via BGP's retry mechanisms.