Hi Thomas, Thanks a lot for your quick response! Jian On 1/22/07, Thomas Hervé <therve@free.fr> wrote:

Quoting jian wu <hellojianwu@gmail.com>:

...

Hi,

Hi,

...

I'm new to Twisted, I only had a limited experience using python and its asyncore/asynchat. I went through Twisted Howto doc.

I just realized that reactor.listenTcp() will only take "listening port" as its parameter. If I want to run a Twisted Program on a machine with multiple network cards(NICs) associated with different IP addresses and I only want my program listening on a specific IP address or NIC, is there a way I can pass listening IP address to reactor.listenTcp() so it'll only accept the connections from a certain NIC/IP Address?

You should have a look at this:

http://twistedmatrix.com/documents/current/api/twisted.internet.interfaces.I...

-- Thomas

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[ John Pote ]: |Hi everyone, |I am putting together a number of servers that will all communicate |with each other every 5 or 10 minutes via TCP/IP connections. It |occured to me that once a connection has been established I might as |well leave it open permanently. Are there any problems/side effects of |doing this? | Is it better policy to close and re-open the connection every now and | then? One advantage of keeping connections opened is to avoid the 3-way handshake that will take place during connection setup. For a few number of conenctions I see no immediate disadvantage, but I guess it all depends on what one means by "few" and the context. |Also am I correct in assuming that if a computer at one end of a |TCP/IPconnection crashes or otherwise becomes unavailable the twisted |program at the other end will only know this when it attempts to send |a packet to the now crashed computer and, having no reply, gets a |timeout. AFAICT, that *is not* a limitation of Twisted. This is simply the fact that TCP -- while a connection is in silence -- will increment its timers, since the rx end-point is unaware if nothing is sent or if the netpath is congested. cheers, Rod Senra ------------- Rodrigo Senra GPr Sistemas http://www.gpr.com.br

On Thu, 15 Feb 2007 15:25:56 +0100, Thomas Jacob <jacob@internet24.de> wrote:

I would implement some sort of keep-alive mechanism for those connections, something that will periodically do some sort of ping/pong sequence (possibly even using TCP's keepalive feature if that is available, anyone know if Twisted can request it on at least some platforms?).

(Cf. for instance this http://libkeepalive.sourceforge.net/docs/TCP-Keepalive-HOWTO )

http://twistedmatrix.com/documents/current/api/twisted.internet.interfaces.I... An application-level keepalive may be more appropriate. If communication happens every 5 to 10 minutes anyway, then a separate keepalive doesn't seem very useful. Your application traffic will let you know when the connection is lost. Then you can reconnect and re-send whatever messages you need to. Jean-Paul

Thanks for all the quick replies. Very helpful, esp the docs links. Initially I will only be using just a 'few' connections, about 4 to 6. Good point about 'stateful packet inspection' as at least one of the servers will be on my home network connecting to the internet via a netgear router. Thanks again, John Thomas Hervé wrote:

Quoting Thomas Jacob <jacob@internet24.de>:

...

I would implement some sort of keep-alive mechanism for those connections, something that will periodically do some sort of ping/pong sequence (possibly even using TCP's keepalive feature if that is available, anyone know if Twisted can request it on at least some platforms?).

Here is documented the setTcpKeepAlive method: http://twistedmatrix.com/documents/current/api/twisted.internet.interfaces.I...

Generally you can enable it in the connectionMade of your protocol.

It occured to me that once a connection has been established I might as well leave it open permanently. Are there any problems/side effects of doing this?

Some firewalls (also inteligent routers) may drop connections which are inactive for a few (5, 10, depending on configurations) minutes. This especially applies in case masquerading is in place.