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       ip [ OPTIONS ] tcp_metrics { COMMAND | help }

       ip tcp_metrics { show | flush } SELECTOR

       ip tcp_metrics delete [ address ] ADDRESS

       SELECTOR := [ [ address ] PREFIX ]


       ip tcp_metrics is used to manipulate entries in the kernel that keep
       TCP information for IPv4 and IPv6 destinations. The entries are created
       when TCP sockets want to share information for destinations and are
       stored in a cache keyed by the destination address. The saved informa-
       tion may include values for metrics (initially obtained from routes),
       recent TSVAL for TIME-WAIT recycling purposes, state for the Fast Open
       feature, etc.  For performance reasons the cache can not grow above
       configured limit and the older entries are replaced with fresh informa-
       tion, sometimes reclaimed and used for new destinations. The kernel
       never removes entries, they can be flushed only with this tool.

   ip tcp_metrics show - show cached entries
       address PREFIX (default)
              IPv4/IPv6 prefix or address. If no prefix is provided all
              entries are shown.

       The output may contain the following information:

       age <S.MMM>sec - time after the entry was created, reset or updated
       with metrics from sockets. The entry is reset and refreshed on use with
       metrics from route if the metrics are not updated in last hour. Not all
       cached values reset the age on update.

       cwnd <N> - CWND metric value

       fo_cookie <HEX-STRING> - Cookie value received in SYN-ACK to be used by
       Fast Open for next SYNs

       fo_mss <N> - MSS value received in SYN-ACK to be used by Fast Open for
       next SYNs

       fo_syn_drops <N>/<S.MMM>sec ago - Number of drops of initial outgoing
       Fast Open SYNs with data detected by monitoring the received SYN-ACK
       after SYN retransmission.  The seconds show the time after last SYN
       drop and together with the drop count can be used to disable Fast Open
       for some time.

       reordering <N> - Reordering metric value

   ip tcp_metrics flush - flush entries
       This command flushes the entries selected by some criteria.

       This command has the same arguments as show.


       ip tcp_metrics show address
           Shows the entries for destinations from subnet

       ip tcp_metrics show
           The same but address keyword is optional

       ip tcp_metrics
           Show all is the default action

       ip tcp_metrics delete
           Removes the entry for from cache.

       ip tcp_metrics flush
           Removes entries for destinations from subnet

       ip tcp_metrics flush all
           Removes all entries from cache

       ip -6 tcp_metrics flush all
           Removes all IPv6 entries from cache keeping the IPv4 entries.




       Original Manpage by Julian Anastasov <ja@ssi.bg>

iproute2 23 Aug 2012 IP-TCP_METRICS(8)

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