Occasionally, when BGP peering between Cisco and Juniper, I’ve run into some issues. The most common is when the Cisco side has their BGP config set to “timers 3 9”, which seems to be a common occurence these days.
The Cisco BGP timers syntax, “neighbor GROUP timers X Y”, specifies keepalive time X (seconds) and hold timers Y (seconds).
The Juniper syntax is “bgp group GROUP hold-time X”, specifies send 3 keepalives within X number of seconds. If the Cisco side is configured for “3 9”, the Juniper side should be set to 9.