08-05-2013
iptables question
I have two programs, a datagram socket based sender and a datagram socket based receiver. The sender emits a short UDP message to 192.168.0.100:33333 every second. The receiver creates a datagram socket with a default port number (let's say it is 44444), clears the iptables adds the following rule:
iptables -t nat -A OUTPUT -p udp --dport 14450 -j REDIRECT --to-ports 44444.
This works great when the receiver is started before the sender, but NOT if the sender is started before the receiver. It looks to me like the iptables are only consulted once on the initial message from the sender but not for any subsequent messages. Is that correct behaviour or did I miss something?
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LEARN ABOUT SUSE
aconnect
aconnect(1) General Commands Manual aconnect(1)
NAME
aconnect - ALSA sequencer connection manager
SYNOPSIS
aconnect [-d] [-options] sender receiver
aconnect -i|-o [-options]
aconnect -x
DESCRIPTION
aconnect is a utility to connect and disconnect two existing ports on ALSA sequencer system. The ports with the arbitrary subscription
permission, such as created by aseqview(1), can be connected to any (MIDI) device ports using aconnect. For example, to connect from port
64:0 to 65:0, run as follows:
% aconnect 64:0 65:0
The connection is one-way, and the whole data to the sender port (64:0) is redirected to the receiver port (65:0). When another port (e.g.
65:1) is attached to the same sender port, the data is sent to both receiver ports. For disconnection, use -d option.
% aconnect -d 64:0 65:0
The address can be given using the client's name.
% aconnect External:0 Emu8000:1
Then the port 0 of the client matching with the string "External" is connected to the port 1 of the client matching with the "Emu8000".
Another function of aconnect is to list the present ports on the given condition. The input ports, which may become sender ports, can be
listed with -i option.
% aconnect -i
client 0: 'System' [type=kernel]
0 'Timer '
1 'Announce '
client 64: 'External MIDI-0' [type=kernel]
0 'MIDI 0-0 '
Similarly, to see the output ports, use -o flag.
You can remove all existing exported connections using -x option. This function is useful for terminating the ALSA drivers, because the
modules with sequencer connections cannot be unloaded unless their connections are removed.
OPTIONS
CONNECTION MANAGEMENT
-d, --disconnect
Disconnect the given subscription.
-e, --exclusive
Connect ports with exclusive mode. Both sender and receiver ports can be no longer connected by any other ports.
-r, --real queue
Convert time-stamps of event packets to the current value of the given real-time queue. This is option is, however, not so useful,
since the receiver port must use (not necessarily own) the specified queue.
-t, --tick queue
Like -r option, but time-stamps are converted to the current value of the given tick queue.
LIST PORTS
-i, --input
List existing input (readable) ports. This option is exclusive to -o.
-o, --output
List existing output (writable) ports. This option is exclusive to -i.
-l, --list
List the current connection status. The connected and connecting ports from/to each port are listed together. The suffix flag [ex]
means the connection is exclusive. The suffix flag [real:#] and [tick:#] mean the connection includes real-time and tick conversion
on the listed queue, respectively.
REMOVE ALL CONNECTIONS
-x, --removeall
Remove all exported connections.
SEE ALSO
aseqnet(1), aseqview(1)
AUTHOR
Takashi Iwai <tiwai@suse.de>
August 31, 2000 aconnect(1)