tcpdrop(8) manual page

Manual Pages — TCPDROP

NAME

tcpdrop – drop TCP connections

SYNOPSIS

tcpdrop local-address local-port foreign-address foreign-port
tcpdrop [-l] -a
tcpdrop [-l] -C cc-algo [-S stack] [-s state]
tcpdrop [-l] [-C cc-algo] -S stack [-s state]
tcpdrop [-l] [-C cc-algo] [-S stack] -s state

DESCRIPTION

The tcpdrop command may be used to drop TCP connections from the command line.

If -a is specified then tcpdrop will attempt to drop all TCP connections.

If -C cc-algo is specified then tcpdrop will attempt to drop all connections using the TCP congestion control algorithm cc-algo.

If -S stack is specified then tcpdrop will attempt to drop all connections using the TCP stack stack.

If -s state is specified then tcpdrop will attempt to drop all TCP connections being in the state state. state is one of SYN_SENT, SYN_RCVD, ESTABLISHED, CLOSE_WAIT, FIN_WAIT_1, CLOSING, LAST_ACK, FIN_WAIT_2, or TIME_WAIT.

If multiple of -C cc-algo, -S stack, and -s state are specified, tcpdrop will attempt to drop all TCP connections using the congestion control algorithm cc-algo, being in the state state, and using the TCP stack stack, if specified. Since TCP connections in the TIME_WAIT state are not tied to any TCP stack, using the option -s TIME_WAIT in combination with the -S stack option results in tcpdrop not dropping any TCP connection.

The -l flag may be given in addition to the -a, -C, -S, or -s options to list the tcpdrop invocation to drop all corresponding TCP connections one at a time.

If none of the -a, -C, -S, or -s options are specified then only the connection between the given local address local-address, port local-port, and the foreign address foreign-address, port foreign-port, will be dropped.

Addresses and ports may be specified by name or numeric value. Both IPv4 and IPv6 address formats are supported.

The addresses and ports may be separated by periods or colons instead of spaces.

EXIT STATUS

The utility exits 0 on success, and >0 if an error occurs.

EXAMPLES

If a connection to httpd(8) is causing congestion on a network link, one can drop the TCP session in charge:

# sockstat -c | grep httpd
www      httpd      16525 3  tcp4 \
        192.168.5.41:80      192.168.5.1:26747

The following command will drop the connection:

# tcpdrop 192.168.5.41 80 192.168.5.1 26747

The following command will drop all connections but those to or from port 22, the port used by sshd(8):

# tcpdrop -l -a | grep -vw 22 | sh

To drop all TCP connections using the new-reno congestion control algorithm use:

# tcpdrop -C new-reno

The following command will drop all connections using the TCP stack rack:

# tcpdrop -S rack

To drop all TCP connections in the LAST_ACK state use:

# tcpdrop -s LAST_ACK

To drop all TCP connections using the congestion control algorithm new-reno and the TCP stack rack and being in the LAST_ACK state use:

# tcpdrop -C new-reno -S rack -s LAST_ACK

AUTHORS

Markus Friedl <Mt markus@openbsd.org> Juli Mallett <Mt jmallett@FreeBSD.org>

TCPDROP (8)

December 4, 2021

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