And any well behaved UDP application would have to implement draft-ietf-tsvwg-datagram-plpmtud.
Cheers, Ole > On 21 Jul 2020, at 18:57, Florin Coras <fcoras.li...@gmail.com> wrote: > > Hi, > > By default udp computes its mss starting from a 1500 mtu. You can avoid this > by either changing the default, i.e., in startup.conf under the udp stanza > add “mtu <value>”, or alternatively you can force mss on each connect, by > explicitly setting it in the remote endpoint’s transport_endpoint_cfg_t > structure. > > If the dgram written through app_send_dgram is shorter than mss, the > session-queue node sends it out as one “packet”, which could be a chained > buffer if mss > ~2kB (default buffer size). IP layer could still decide to > fragment the resulting buffer, subject to the output interface’s mtu. > Otherwise, i.e. dgram larger than mss, session-queue forcefully fragments the > dgram, this is probably something that you don’t want. > > Regards, > Florin > >> On Jul 21, 2020, at 5:07 AM, jiangxiaom...@outlook.com wrote: >> >> hi: >> When sending 1500 bytes data with session app_send_dgram api, I find >> session-queue node will split the data to two udp packets, then vpp will >> sending to two separate IP packets out with no fragmentation. Even I set >> interface MTU with 9000, It's still sending two separate IP packets. I think >> the way session-queue process the app_send_dgram data have two logic logic >> bug. >> 1. If app_send_dgram's sending length more then snd_mss, session-queue >> should do udp fragmentation, rather simplely separating to other udp packets. >> 2. if app_send_dgram's sending length less then interface's MTU, >> session-queue should sending one ip packet out. But the MTU seems have no >> effect on session-queue. >> >> Below is the debug log: >> DBGvpp# trace add session-queue 20 >> DBGvpp# sh trace >> ------------------- Start of thread 0 vpp_main ------------------- >> No packets in trace buffer >> ------------------- Start of thread 1 vpp_wk_0 ------------------- >> Packet 1 >> >> 00:06:06:009843: session-queue >> session index 0 thread index 1 >> 00:06:06:009860: ip4-lookup >> fib 0 dpo-idx 1 flow hash: 0x00000000 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 1500, checksum 0x0000 (should be 0x25f7) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 1480, checksum 0x0000 >> 00:06:06:009868: ip4-rewrite >> tx_sw_if_index 1 dpo-idx 1 : ipv4 via 192.168.7.100 eth0: mtu:9000 next:3 >> 0000000000010000000000020800 flow hash: 0x00000000 >> 00000000: 0000000000010000000000020800450005dc00000000ff110000c0a80765c0a8 >> 00000020: 076431c201f405c80000010101010101010101010101010101010101 >> 00:06:06:009873: eth0-output >> eth0 >> IP4: 00:00:00:00:00:02 -> 00:00:00:00:00:01 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 1500, checksum 0x0000 (should be 0x25f7) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 1480, checksum 0x0000 >> 00:06:06:009878: eth0-tx >> eth0 tx queue 1 >> buffer 0x27685e: current data 98, length 1514, buffer-pool 0, ref-count 1, >> trace handle 0x1000000 >> local ip4 offload-ip-cksum offload-udp-cksum >> l3-hdr-offset 112 l4-hdr-offset 132 >> PKT MBUF: port 65535, nb_segs 1, pkt_len 1514 >> buf_len 2176, data_len 1514, ol_flags 0xf0000000000000, data_off 226, >> phys_addr 0x47a1800 >> packet_type 0x0 l2_len 14 l3_len 20 outer_l2_len 0 outer_l3_len 0 >> rss 0x0 fdir.hi 0x0 fdir.lo 0x0 >> Packet Offload Flags >> PKT_TX_IP_CKSUM (0x0000) IP cksum of TX pkt. computed by NIC >> PKT_TX_TCP_CKSUM (0x0000) TCP cksum of TX pkt. computed by NIC >> PKT_TX_SCTP_CKSUM (0x0000) SCTP cksum of TX pkt. computed by NIC >> IP4: 00:00:00:00:00:02 -> 00:00:00:00:00:01 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 1500, checksum 0x0000 (should be 0x25f7) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 1480, checksum 0x95f3 >> >> Packet 2 >> >> 00:06:06:009940: session-queue >> session index 0 thread index 1 >> 00:06:06:009949: ip4-lookup >> fib 0 dpo-idx 1 flow hash: 0x00000000 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 66, checksum 0x0000 (should be 0x2b91) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 46, checksum 0x0000 >> 00:06:06:009952: ip4-rewrite >> tx_sw_if_index 1 dpo-idx 1 : ipv4 via 192.168.7.100 eth0: mtu:9000 next:3 >> 0000000000010000000000020800 flow hash: 0x00000000 >> 00000000: 00000000000100000000000208004500004200000000ff110000c0a80765c0a8 >> 00000020: 076431c201f4002e0000010101010101010101010101010101010101 >> 00:06:06:009954: eth0-output >> eth0 >> IP4: 00:00:00:00:00:02 -> 00:00:00:00:00:01 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 66, checksum 0x0000 (should be 0x2b91) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 46, checksum 0x0000 >> 00:06:06:009956: eth0-tx >> eth0 tx queue 1 >> buffer 0x276837: current data 98, length 80, buffer-pool 0, ref-count 1, >> trace handle 0x1000001 >> local ip4 offload-ip-cksum offload-udp-cksum >> l3-hdr-offset 112 l4-hdr-offset 132 >> PKT MBUF: port 65535, nb_segs 1, pkt_len 80 >> buf_len 2176, data_len 80, ol_flags 0xf0000000000000, data_off 226, >> phys_addr 0x47a0e40 >> packet_type 0x0 l2_len 14 l3_len 20 outer_l2_len 0 outer_l3_len 0 >> rss 0x0 fdir.hi 0x0 fdir.lo 0x0 >> Packet Offload Flags >> PKT_TX_IP_CKSUM (0x0000) IP cksum of TX pkt. computed by NIC >> PKT_TX_TCP_CKSUM (0x0000) TCP cksum of TX pkt. computed by NIC >> PKT_TX_SCTP_CKSUM (0x0000) SCTP cksum of TX pkt. computed by NIC >> IP4: 00:00:00:00:00:02 -> 00:00:00:00:00:01 >> UDP: 192.168.7.101 -> 192.168.7.100 >> tos 0x00, ttl 255, length 66, checksum 0x0000 (should be 0x2b91) dscp >> CS0 ecn NON_ECN >> fragment id 0x0000 >> UDP: 12738 -> 500 >> length 46, checksum 0x9059 >> >> DBGvpp# sh int >> Name Idx State MTU (L3/IP4/IP6/MPLS) >> Counter Count >> eth0 1 up 9000/0/0/0 rx >> packets 164 >> rx bytes >> 16136 >> tx >> packets 9 >> tx bytes >> 6428 >> drops >> 164 >> ip4 >> 102 >> ip6 >> 62 >> local0 0 down 0/0/0/0 drops >> 2 >> DBGvpp# sh session verbose >> Thread 0: no sessions >> >> Connection State Rx-f >> Tx-f >> [1:0][U] 192.168.7.101:12738->192.168.7.100:500 OPENED 0 0 >> >> Thread 1: active sessions 1 >> DBGvpp# >> > >
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