.TH "IP\-TCP_METRICS" 8 "23 Aug 2012" "iproute2" "Linux"

.SH "NAME"

ip-tcp_metrics \- management for TCP Metrics

.SH "SYNOPSIS"

.sp

.ad l

.in +8

.ti -8

.B ip

.RI "[ " OPTIONS " ]"

.B tcp_metrics

.RI "{ " COMMAND " | "

.BR help " }"

.sp

.ti -8

.BR "ip tcp_metrics" " { " show " | " flush " }

.IR SELECTOR

.ti -8

.BR "ip tcp_metrics delete " [ " address " ]

.IR ADDRESS

.ti -8

.IR SELECTOR " := "

.RB "[ [ " address " ] "

.IR PREFIX " ]"

.SH "DESCRIPTION"

.B 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.

.SS ip tcp_metrics show - show cached entries

.TP

.BI address " PREFIX " (default)

IPv4/IPv6 prefix or address. If no prefix is provided all entries are shown.

.LP

The output may contain the following information:

.BI 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.

.BI cwnd " <N>"

- CWND metric value

.BI fo_cookie " <HEX-STRING>"

- Cookie value received in SYN-ACK to be used by Fast Open for next SYNs

.BI fo_mss " <N>"

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

.BI 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.

.BI reordering " <N>"

- Reordering metric value

.BI rtt " <N>" us

- RTT metric value

.BI rttvar " <N>" us

- RTTVAR metric value

.BI ssthresh " <SSTHRESH>"

- SSTHRESH metric value

.BI tw_ts " <TSVAL>/<SEC>" "sec ago"

- recent TSVAL and the seconds after saving it into TIME-WAIT socket

.SS ip tcp_metrics delete - delete single entry

.TP

.BI address " ADDRESS " (default)

IPv4/IPv6 address. The address is a required argument.

.SS ip tcp_metrics flush - flush entries

This command flushes the entries selected by some criteria.

.PP

This command has the same arguments as

.B show.

.SH "EXAMPLES"

.PP

ip tcp_metrics show address 192.168.0.0/24

.RS 4

Shows the entries for destinations from subnet

.RE

.PP

ip tcp_metrics show 192.168.0.0/24

.RS 4

The same but address keyword is optional

.RE

.PP

ip tcp_metrics

.RS 4

Show all is the default action

.RE

.PP

ip tcp_metrics delete 192.168.0.1

.RS 4

Removes the entry for 192.168.0.1 from cache.

.RE

.PP

ip tcp_metrics flush 192.168.0.0/24

.RS 4

Removes entries for destinations from subnet

.RE

.PP

ip tcp_metrics flush all

.RS 4

Removes all entries from cache

.RE

.PP

ip -6 tcp_metrics flush all

.RS 4

Removes all IPv6 entries from cache keeping the IPv4 entries.

.RE

.SH SEE ALSO

.br

.BR ip (8)

.SH AUTHOR

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