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 entriesaddress 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 entryaddress 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 192.168.0.0/24
Shows the entries for destinations from subnet
ip tcp_metrics show 192.168.0.0/24
The same but address keyword is optional
Show all is the default action
ip tcp_metrics delete 192.168.0.1
Removes the entry for 192.168.0.1 from cache.
ip tcp_metrics flush 192.168.0.0/24
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.
This page is part of the iproute2 (utilities for controlling TCP/IP
networking and traffic) project. Information about the project can
be found at
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iproute2 23 Aug 2012 IP-TCP_METRICS(8)