Created attachment 197 [details] pcap with 1 packet ~9000B Here is example of MTU (max-pkt-len) set to ~300B but driver receives packet of ~9000B (the jumbo pcap is attached) <code> root@u18c_9td3:/home/cgs/workspace/master/jumbo# ./dpdk-testpmd --no-huge -m1024 -l 0-3 -n 4 --vdev 'net_pcap0,rx_pcap=jumbo_9000.pcap,tx_pcap=file_tx.pcap' -- --no-flush-rx --total-num-mbufs=2048 --max-pkt-len=300 -i EAL: Detected CPU lcores: 6 EAL: Detected NUMA nodes: 1 EAL: Detected static linkage of DPDK EAL: Multi-process socket /var/run/dpdk/rte/mp_socket EAL: Selected IOVA mode 'VA' EAL: VFIO support initialized TELEMETRY: No legacy callbacks, legacy socket not created Interactive-mode selected Warning: NUMA should be configured manually by using --port-numa-config and --ring-numa-config parameters along with --numa. testpmd: create a new mbuf pool <mb_pool_0>: n=2048, size=2176, socket=0 testpmd: preferred mempool ops selected: ring_mp_mc Warning! port-topology=paired and odd forward ports number, the last port will pair with itself. Configuring Port 0 (socket 0) Port 0: 02:70:63:61:70:00 Checking link statuses... Done testpmd> show port info 0 ********************* Infos for port 0 ********************* MAC address: 02:70:63:61:70:00 Device name: net_pcap0 Driver name: net_pcap Firmware-version: not available Devargs: rx_pcap=jumbo_9000.pcap,tx_pcap=file_tx.pcap Connect to socket: 0 memory allocation on the socket: 0 Link status: up Link speed: 10 Gbps Link duplex: full-duplex Autoneg status: Off MTU: 282 Promiscuous mode: enabled Allmulticast mode: enabled Maximum number of MAC addresses: 1 Maximum number of MAC addresses of hash filtering: 0 VLAN offload: strip off, filter off, extend off, qinq strip off No RSS offload flow type is supported. Minimum size of RX buffer: 0 Maximum configurable length of RX packet: 4294967295 Maximum configurable size of LRO aggregated packet: 0 Current number of RX queues: 1 Max possible RX queues: 1 Max possible number of RXDs per queue: 65535 Min possible number of RXDs per queue: 0 RXDs number alignment: 1 Current number of TX queues: 1 Max possible TX queues: 1 Max possible number of TXDs per queue: 65535 Min possible number of TXDs per queue: 0 TXDs number alignment: 1 Max segment number per packet: 65535 Max segment number per MTU/TSO: 65535 Device capabilities: 0x0( ) testpmd> set verbose 3 Change verbose level from 0 to 3 testpmd> start io packet forwarding - ports=1 - cores=1 - streams=1 - NUMA support enabled, MP allocation mode: native Logical Core 1 (socket 0) forwards packets on 1 streams: RX P=0/Q=0 (socket 0) -> TX P=0/Q=0 (socket 0) peer=02:00:00:00:00:00 io packet forwarding packets/burst=32 nb forwarding cores=1 - nb forwarding ports=1 port 0: RX queue number: 1 Tx queue number: 1 Rx offloads=0x0 Tx offloads=0x0 RX queue: 0 RX desc=0 - RX free threshold=0 RX threshold registers: pthresh=0 hthresh=0 wthresh=0 RX Offloads=0x0 TX queue: 0 TX desc=0 - TX free threshold=0 TX threshold registers: pthresh=0 hthresh=0 wthresh=0 TX offloads=0x0 - TX RS bit threshold=0 testpmd> port 0/queue 0: received 1 packets src=04:F4:BC:3E:E4:25 - dst=00:00:00:00:00:00 - type=0x0800 - length=8996 - nb_segs=5 - timestamp 1266577613728443 - sw ptype: L2_ETHER L3_IPV4 - l2_len=14 - l3_len=20 - Receive queue=0x0 ol_flags: RTE_MBUF_F_RX_L4_CKSUM_UNKNOWN RTE_MBUF_F_RX_IP_CKSUM_UNKNOWN RTE_MBUF_F_RX_OUTER_L4_CKSUM_UNKNOWN port 0/queue 0: sent 1 packets src=04:F4:BC:3E:E4:25 - dst=00:00:00:00:00:00 - type=0x0800 - length=8996 - nb_segs=5 - timestamp 1266577613728443 - sw ptype: L2_ETHER L3_IPV4 - l2_len=14 - l3_len=20 - Send queue=0x0 ol_flags: RTE_MBUF_F_TX_L4_NO_CKSUM testpmd> stop Telling cores to stop... Waiting for lcores to finish... ---------------------- Forward statistics for port 0 ---------------------- RX-packets: 1 RX-dropped: 0 RX-total: 1 TX-packets: 1 TX-dropped: 0 TX-total: 1 ---------------------------------------------------------------------------- +++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++ RX-packets: 1 RX-dropped: 0 RX-total: 1 TX-packets: 1 TX-dropped: 0 TX-total: 1 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Done. testpmd> show port stats 0 ######################## NIC statistics for port 0 ######################## RX-packets: 1 RX-missed: 0 RX-bytes: 8996 RX-errors: 0 RX-nombuf: 0 TX-packets: 1 TX-errors: 0 TX-bytes: 8996 Throughput (since last show) Rx-pps: 0 Rx-bps: 0 Tx-pps: 0 Tx-bps: 0 ############################################################################ testpmd> quit Stopping port 0... Stopping ports... Done Shutting down port 0... Closing ports... Port 0 is closed Done Bye... There's further issues for apps (non test-pmd) that use pcap driver as they may unexpectedly get segmented mbufs w/o setting RTE_ETH_RX_OFFLOAD_SCATTER
In DPDK there is no requirement that network device drivers drop packets larger than MTU. PS: Same applies to Linux network devices. The driver does need a check to make sure not to scatter unless enabled.