Provided by: iproute2_5.15.0-1ubuntu2_amd64 bug


       ip-tcp_metrics - management for TCP Metrics


       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 information 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 information, 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

       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

       rtt <N>us - RTT metric value

       rttvar <N>us - RTTVAR metric value

       ssthresh <SSTHRESH> - SSTHRESH metric value

       tw_ts <TSVAL>/<SEC>sec ago - recent TSVAL and the seconds after saving it into TIME-WAIT

   ip tcp_metrics delete - delete single entry
       address ADDRESS (default)
              IPv4/IPv6 address. The address is a required argument.

   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 <>