Thanks for your comment. The vast majority of networks outside of GCE don't use an MTU of 1460. Even if we set the instance MTU size to 1460, we still have problems. If a UDP packet sent to a GCE instance from outside GCE is larger than GCE's MTU, the first fragment is received and no subsequent fragments ever make it to the instance. This is the bug. This is very common with protocols like SIP when the SDP gets large due to a lot of media attributes.