MPCs (Modular Port Concentrators) installed in an MX Series router may crash upon receipt of very specific and unlikely route prefix install/delete actions, such as a BGP routing update. The set of route prefix updates appears to be non-deterministic. Junos versions affected include 10.0, 10.1, 10.2, 10.3, 10.4 prior to 10.4R6, and 11.1 prior to 11.1R4. The trigger for the MPC crash was determined to be a valid BGP UPDATE received from a registered network service provider, although this one UPDATE was determined to not be solely responsible for the crashes. A complex sequence of preconditions is required to trigger this crash. Both IPv4 and IPv6 routing prefix updates can trigger this MPC crash.