I am currently trying to figure out why one of the pyverbs tests is failing. I added a check implementing C9-205 (p 419) of the IBA spec. I requires that a responder receiving a packet longer than the receive buffer or the PMTU shall be silently dropped. I.e. a class D error. C9-205: Before executing the request, the responder shall validate the Packet Length field of the LRH and the PadCnt of the BTH as described in 9.8.3.2.2: Responder - Length Validation. The following characteristics shall be validated: • The Length fields shall be checked to confirm that there is sufficient space available in the receive buffer specified by the receive WQE. • The packet payload length must be between zero and PMTU bytes inclusive in size. If a packet is detected with an invalid length, the request shall be an invalid request and it shall be silently dropped by the responder as specified in Section 9.9.3 Responder Side Behavior on page 435. The responder then waits for a new request packet. tests/test_cq_events.py passes PATH_MTU = 1024 in the modify QPs verb for RC and XRC but not UD. This should be a required parameter as part of the primary destination address but is not getting set for UD. The test then proceeds to send a 1024 byte payload to the destination and for UD hangs waiting for the completion. I don't want to mess with these tests because I am a poor python coder. Is there some reason why it is OK to not set the PMTU for UD QPs? Bob