Valdis.Kletnieksat_private wrote: > On Fri, 13 Sep 2002 13:59:53 +0200, Volker Tanger said: > > >>Had this phenomenon once or twice. The timeout may happen if the sending >>party is much slower than the reveiving one AND the receiving one also >>is the listening nc. > > > OK.. either I'm dense or I've not had enough caffeine. How do you set up > a situation where the receiving netcat *isnt* the listening one? In other > words, under what situations is the 'AND' clause *not* true? Slow-Server: dd if=/dev/hda | bzip2 -c | nc -p 12345 -l Fast-Client: nc SERVER 12345 > image.bz2 Basically you should build the queue continuously (!) degrading to from fast to slow. The sample above should then read as follow, if you aim for reliable network connection: Slow-Server: cat image.bz2 | nc CLIENT 12345 Fast-Client: nc -p 12345 -l | bzip2 -c > image.bz2 This way there always is data "waiting at the door" to be received. In the first sample the nc client is "torn" between the slow server and the speeding local HD. This setup simply is calling for timeouts. More Netact imaging fun (okay, I was trying to play dirty here): I once tried to chain clients like Master: dd if=/dev/hda | nc CLIENT#1 1111 Client#1: dd -p 1111 -l | tee /dev/hda | nc CLIENT#2 2222 Client#2: dd -p 2222 -l | tee /dev/hda | nc CLIENT#3 3333 Client#3: dd -p 3333 -l | tee /dev/hda ...... which failed to complete all times I tried. Always there was a timeout somewhere. Even extraordinary timeouts (-w 28800 = 8 hours) did not help. Identical hardware on all parts, so no speed difference here. I finally settled with putting a GZIPped image on a server and then feeding the clients from there, unbzip2ing the image on the clients. With the same hardware I easily could serve ~150 clients this way - much more reliable and additionaly more flexible than the daisy chain tried above. Bye Volker Tanger IT-Security Consulting -- discon gmbh Wrangelstraße 100 D-10997 Berlin fon +49 30 6104-3307 fax +49 30 6104-3461 volker.tangerat_private http://www.discon.de/ ----------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
This archive was generated by hypermail 2b30 : Fri Sep 13 2002 - 09:17:42 PDT