上次没查到根本原因，这次继续排查，发现和我们发的包有很大的关系，根据上次rx_drop的含义，丢的数据可能是以下几种原因：
The softnet backlog full
Bad VLAN tags
Packets received with unknown or unregistered protocols
IPv6 frames when the server is configured only for ipv4
一 dropwatch使用
1.1 使用
丢包排查的神器，上篇已经说过，这次在仔细用以下，dropwatch目前要求首先内核必须大于等于2.6.30。
yum install dropwatch
采用交互方式运行：
[root@localhost ~]# dropwatch -l kas
>start
启动，按ctrl+C停止。
dropwatch> start
Enabling monitoring...
Kernel monitoring activated.
Issue Ctrl-C to stop monitoring
15 drops at ip6_mc_input+1ad (0xffffffff8164414d)
117 drops at ip_rcv+cf (0xffffffff815ca47f)
2 drops at __udp4_lib_mcast_deliver+2ad (0xffffffff815fbe3d)
6 drops at ip_rcv_finish+1b4 (0xffffffff815c9e04)
2 drops at __netif_receive_skb_core+3d2 (0xffffffff81586d82)
2 drops at ip_forward+1d0 (0xffffffff815cbee0)
1 drops at skb_queue_purge+18 (0xffffffff81572ec8)
13 drops at ip_rcv_finish+1b4 (0xffffffff815c9e04)
7 drops at tcp_v4_rcv+87 (0xffffffff815f0197)
25 drops at ip6_mc_input+1ad (0xffffffff8164414d)
15 drops at ip_rcv_finish+1b4 (0xffffffff815c9e04)
118 drops at ip_rcv+cf (0xffffffff815ca47f)
3 drops at ip_forward+1d0 (0xffffffff815cbee0)
1 drops at __brk_limit+3e1e36a8 (0xffffffffc05f46a8)
1 drops at __netif_receive_skb_core+3d2 (0xffffffff81586d82)
4 drops at ip_rcv_finish+1b4 (0xffffffff815c9e04)
7 drops at tcp_v4_rcv+87 (0xffffffff815f0197)
17 drops at ip6_mc_input+1ad (0xffffffff8164414d)
112 drops at ip_rcv+cf (0xffffffff815ca47f)
6 drops at ip_forward+1d0 (0xffffffff815cbee0)
5 drops at ip_rcv_finish+1b4 (0xffffffff815c9e04)
丢包主要几种在：118 drops at ip_rcv+cf (0xffffffff815ca47f)这个函数，查看drop位置：
#grep -w "ip_rcv" /boot/System.map-$(uname -r) -A10
ffffffff815ca3b0 T ip_rcv
ffffffff815ca7c0 t ip4_frag_match
ffffffff815ca810 t ipqhashfn
ffffffff815ca8c0 t ip4_hashfn
ffffffff815ca8f0 t ip4_frag_free
ffffffff815ca910 t ip4_frag_init
ffffffff815ca9f0 t ipv4_frags_exit_net
ffffffff815caa30 t ipv4_frags_init_net
ffffffff815cab30 t ip_expire
ffffffff815cac50 T ip_defrag
ffffffff815cba30 T ip_check_defrag
我们注意到0xffffffff815ca47f在ffffffff815ca3b0和ffffffff815ca7c0之间。
如果dropwatch显示的地址，则可以通过以下命令进行定位：
cat /proc/kallsyms|grep xxx(地址前面xx位)
找下内核源码去查看：
找到相应版本后，搜索ip_rcv
[https://elixir.bootlin.com/linux/v3.10.69/source/net/ipv4/ip_input.c#L375](https://elixir.bootlin.com/linux/v3.10.69/source/net/ipv4/ip_input.c#L375)
内核ip_rcv代码
大概是pkt_type类型不对,丢弃掉不是发往本机的报文，skb->pkt_type在网卡接收报文处理以太网头时会根据dst mac设置，协议栈的书会讲不是发往本机的广播报文会在二层被丢弃，但是这个和我们的不符合，我们是采用混杂模式，所以不存在mac不匹配的问题。
二 其他丢包查询办法
2.1 ip查看丢包
$ip -s -s link ls eno2
24: eno2: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT qlen 1000
link/ether 78:ac:44:0f:16:00 brd ff:ff:ff:ff:ff:ff
RX: bytes packets errors dropped overrun mcast
16179332325329 79927306089 0 123106137 0 315991391
RX errors: length crc frame fifo missed
0 0 0 0 0
TX: bytes packets errors dropped carrier collsns
0 0 0 0 0 0
TX errors: aborted fifo window heartbeat transns
0 0 0 0 8
2.2 netstat 查看丢包情况
$ netstat -i
Kernel Interface table
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
eno1 1500 132108 0 24242 0 7034 0 0 0 BMRU
eno2 1500 80057630017 0 123636508 0 0 0 0 0 BMPRU
eno3 1500 173704853 0 527651 0 52369033 0 0 0 BMPRU
eno4 1500 8497 0 0 0 0 0 0 0 BMU
enp59s0f0 1500 0 0 0 0 0 0 0 0 BMU
enp59s0f1 1500 0 0 0 0 0 0 0 0 BMU
lo 65536 581220807 0 0 0 581220807 0 0 0 LRU
vboxnet0 1500 0 0 0 0 20880 0 0 0 BMRU
virbr0 1500 0 0 0 0 0 0 0 0 BMU
2.3 查看具体协议的丢包
比如udp丢包
netstat -su
IcmpMsg:
InType0: 112
InType3: 165692
InType8: 7
InType11: 7434
OutType0: 7
OutType3: 169248
OutType5: 7
OutType8: 153
Udp:
126528161 packets received
77827 packets to unknown port received.
20408348 packet receive errors
120504641 packets sent
20408348 receive buffer errors
0 send buffer errors
UdpLite:
IpExt:
InNoRoutes: 4
InMcastPkts: 26550045
OutMcastPkts: 2576
InBcastPkts: 456933
OutBcastPkts: 36
InOctets: 1176854170075
OutOctets: 1113352074110
InMcastOctets: 7163508127
OutMcastOctets: 165775
InBcastOctets: 138811485
OutBcastOctets: 2808
InCsumErrors: 21934887
InNoECTPkts: 1058031660
InECT0Pkts: 2361
2.4查看各个协议的收发情况
#cat /proc/net/snmp
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests OutDiscards OutNoRoutes ReasmTimeout ReasmReqds ReasmOKs ReasmFails FragOKs FragFails FragCreates
Ip: 1 64 1054834458 21934887 0 5631 159 0 652874483 636977013 0 52 256 3409 889 256 7277 0 23887
Icmp: InMsgs InErrors InCsumErrors InDestUnreachs InTimeExcds InParmProbs InSrcQuenchs InRedirects InEchos InEchoReps InTimestamps InTimestampReps InAddrMasks InAddrMaskReps OutMsgs OutErrors OutDestUnreachs OutTimeExcds OutParmProbs OutSrcQuenchs OutRedirects OutEchos OutEchoReps OutTimestamps OutTimestampReps OutAddrMasks OutAddrMaskReps
Icmp: 173245 34807 0 165692 7434 0 0 0 7 112 0 0 0 0 169415 0 169248 0 0 0 7 153 7 0 0 0 0
IcmpMsg: InType0 InType3 InType8 InType11 OutType0 OutType3 OutType5 OutType8
IcmpMsg: 112 165692 7 7434 7 169248 7 153
Tcp: RtoAlgorithm RtoMin RtoMax MaxConn ActiveOpens PassiveOpens AttemptFails EstabResets CurrEstab InSegs OutSegs RetransSegs InErrs OutRsts InCsumErrors
Tcp: 1 200 120000 -1 547226 349549 365407 43767 184 505212431 516379275 219665 0 489834 0
Udp: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors
Udp: 126561398 77827 20408348 120536958 20408348 0 0
UdpLite: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors
UdpLite: 0 0 0 0 0 0 0
