IP-TCP_METRICS(8)                   Linux                  IP-TCP_METRICS(8)

NAME         top

       ip-tcp_metrics - management for TCP Metrics

SYNOPSIS         top

       ip [ OPTIONS ] tcp_metrics { COMMAND | help }

       ip tcp_metrics { show | flush } SELECTOR

       ip tcp_metrics delete [ address ] ADDRESS

       SELECTOR := [ [ address ] PREFIX ]

DESCRIPTION         top

       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

   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

       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 socket

   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.

EXAMPLES         top

       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.

SEE ALSO         top


AUTHOR         top

       Original Manpage by Julian Anastasov <>

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       If you have a bug report for this manual page, send it to,  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on
       2020-02-08.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-01-29.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

iproute2                         23 Aug 2012               IP-TCP_METRICS(8)

Pages that refer to this page: ip(8)