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ss --info returns information about tcp connections. It produces a line simliar to the following (some fields removed for formatting)

tcp ESTAB 0 0 192.168.1.177:60236 54.70.141.88:https cubic wscale:7,7 rto:204 rtt:0.918/0.419 reordering:59

What exactly does the reordering number mean in this example?

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From TCP Variables:

The tcp_reordering variable tells the kernel how much a TCP packet may be reordered in a stream without assuming that the packet was lost somewhere on the way.

tcp_reordering may be changed via net.ipv4.tcp_reordering variable of sysctl. By default this value is 3.

If you change net.ipv4.tcp_reordering variable, then ss --info will print all connections with values which are differs from 3. Fragment of iproute2 source:

. . .
if (s->reordering != 3)
        printf(" reordering:%d", s->reordering);
. . .
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  • Thanks for the link, that's really useful.
    – timlyo
    Jul 17, 2019 at 12:40
  • @timlyo You are welcome! Jul 17, 2019 at 12:40

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