TCP ACK窗口收缩

Question

(注意:我不是网络工程师)我们正在向外部供应商发送文件，并对不同的服务进行随机超时。似乎我们经常在较大的文件上超时。我们捕获了一个数据包，它显示了我们的窗口正在缩小，并怀疑小的有效载荷在窗口达到0之前就完成了，其中大的有效载荷给了我们一个RST。

    11369 > su-mit-tg [ACK] Seq=677231 Ack=253694 Win=32768 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=256614 Win=29848 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=259534 Win=26928 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=262454 Win=24008 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=265374 Win=21088 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=268294 Win=18168 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=271214 Win=15248 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=274134 Win=12328 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=277054 Win=9408 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=279974 Win=6488 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=282894 Win=3568 Len=0
    11369 > su-mit-tg [ACK] Seq=677231 Ack=285814 Win=648 Len=0

编辑:我指的是我们从应用程序中调用的不同的web服务。超时并不总是在特定服务上失败，而是在不同的时间命中所有服务。我不能从不同的网络发送它。

Answer 1

我认为这个问题与IO问题或应用程序问题有关，而且出于任何原因，套接字缓冲区已经完成了空间。

我这样做是为了在linux中重现与IO相关的问题：

/dev/vdb                 2.0G  1.6G  470M  77% /brick1

[root@nod01 ~]# ls -l /dev/vdb
brw-rw---- 1 root disk 252, 16 Apr 19 22:46 /dev/vdb

echo "252:16 $((1024*250))" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device ## Limit write to 250KB per second

cd /brick1 ## change directory for downloading the Centos Iso


wget ftp://mirror.fdcservers.net/centos/6.4/isos/x86_64/CentOS-6.4-x86_64-bin-DVD2.iso


00:19:58.992042 IP mirror.50966 > nod01.example.com.46637: Flags [.], ack 1, win 46, options [nop,nop,TS val 2662018758 ecr 5131800], length 0
00:19:58.992107 IP nod01.example.com.46637 > mirror.50966: Flags [.], ack 11256736, win 0,  options [nop,nop,TS val 5144749 ecr 2661992655], length 0 ## I'm telling to the sender, please don't send me more data, because my socket buffer is full


[root@nod01 ~]# netstat -tunap | grep wget
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    

tcp   5264896      0 192.168.122.244:46637   208.53.158.34:50966     ESTABLISHED 15574/wget          #### note the sender has 5M of data in the doesn't buffer, because it cannot write fast in /brick1 as data arrive
tcp        0      0 192.168.122.244:51331   208.53.158.34:21        ESTABLISHED 15574/wget