TCP/IP questions

Malcolm Clarke malcolm.clarke at
Thu Nov 8 04:27:35 PST 2007

Dear Bram

You may need to describe your intention more clearly.

If you detach the network cable, the hardware will detect the disconnect 
and reset the hardware, which will provide an indicate to the higher 
layers to reset also. Reconnecting the cable will be seen as a new 
connection and it will perform initialisation (eg DHCP, etc). All TCP 
connections will be closed, etc.

If it is the case that you are trying to test behaviour of an 
application to the effects of loss of packets then you will need a 
different approach.

We use the IPFW firewall and set up pipes that can be configured to 
artificially lose packets, restrict BW or even close (hence my question 
to the group). Alternatively you must arrange to break the connection 
elsewhere, say on the otherside of a switch, taking care not to break 
the physical connetion to the far end to create a disconnect that does 
not reset the hardware..



Nikos Vassiliadis wrote:

>On Wednesday 07 November 2007 18:02:44 Bram wrote:
>>Hi all,
>>Can you change the timeout for a tcp connection ?
>>I need to do the following: start a tcp connection , unplug the network
>>cable (it's actually wifi but the effect is the same),send some data
>>over the connection,wait 20 seconds , reinsert the network cable and
>>just keep working.
>>When you normally do this the connection will be dead.
>>Is there a way in freebsd to change this ? are there parameters wich you
>>can set so that the above would work (20 seconds without network can
>>happen) ?
>TCP using the default FreeBSD settings, can survive
>20 secs of inactivity. It can be an application forced
>timeout. What application/protocol are talking about?
>freebsd-questions at mailing list
>To unsubscribe, send any mail to "freebsd-questions-unsubscribe at"

Dr Malcolm Clarke
Senior Lecturer in Data Communication Systems and Telemedicine
Department of Information Systems and Computing
Brunel University

Tel: +44 1895 265053
Fax: +44 1895 251686


More information about the freebsd-questions mailing list