IP-TCP_METRICS(8) Linux IP-TCP_METRICS(8)
NAME
ip-tcp_metrics - management for TCP Metrics
SYNOPSIS
ip [ OPTIONS ] tcp_metrics { COMMAND | help }
ip tcp_metrics { show | flush } SELECTOR
ip tcp_metrics delete [ address ] ADDRESS
SELECTOR := [ [ address ] PREFIX ]
DESCRIPTION
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 in-
clude 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 re-
claimed 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 met-
rics 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 af-
ter 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
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
ip tcp_metrics
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.
SEE ALSO
ip(8)
AUTHOR
Original Manpage by Julian Anastasov <ja@ssi.bg>
iproute2 23 Aug 2012 IP-TCP_METRICS(8)
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