Use the key and lookup table lengths returned by GET_VF_RESOURCES when configuring RSS through virtchnl, as DPDK does. The Windows E835 PF advertises a 40-byte key and rejects our fixed 52-byte CONFIG_RSS_KEY request, leaving receive traffic on queue zero. Validate the negotiated lengths before constructing AdminQ messages and publish the lookup table size to iflib. Preserve register-mode RSS selection and its fixed hardware sizes. Use aligned, zero initialized key storage so an RSS kernel's 40-byte key does not leave an uninitialized tail when the PF requests 52 bytes. Validation: normal and RSS enabled iavf module builds passed. On an E835 VF under Hyper-V Server 2025, repeated IPv4 and IPv6 receive tests used all three configured guest RX queues in both transparent hn and non-transparent lagg modes. The RSS key rejection disappeared, IPv4 transmit tests passed, and no TX watchdog fired. Each traffic case used three runs of 16 streams. Obtained from: DPDK (negotiated RSS sizing) MFC after: 2 weeks Sponsored by: BBOX.io