Re: RE : [lwip-users] Questions about LwIP KEEPALIVE...

[Kieran Mansley]

On Thu, 2007-02-15 at 18:29 +0100, Frédéric BERNON wrote:
> Ok, I didn't think that was to be RFC compliant...
> 
> But don't you think these values would have to be settable in lwipopts.h ? 
> Because, even with TCP_KEEPALIVE to 0, the minimum delay to detect a loss of 
> stream connection is TCP_MAXIDLE (75000*9 = 675000ms =~ 11.25 min).
> 
> 
> /* Keepalive values */
> #define  TCP_KEEPINTVL     75000                         /* Time between 
> KEEPALIVE probes in miliseconds */
> #define  TCP_KEEPCNT       9                             /* Counter for 
> KEEPALIVE probes */
> #define  TCP_MAXIDLE       TCP_KEEPCNT * TCP_KEEPINTVL   /* Maximum KEEPALIVE 
> probe time */
> 
> 
> On a basic XP pc (yes, I know, this is not the "best" reference), registry 
> values (in 
> "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\TCPIP\Parameters") 
> seems to be TCP_KEEPCNT=5 ("TcpMaxDataRetransmissions"), TCP_KEEPINTVL=1000 
> ("KeepAliveInterval"), and TCP_KEEPDEFAULT=7200000 ("KeepAliveTime"). 
> http://support.microsoft.com/kb/314053/en-us 
> 
> What do you think about this idea?

It's not an option that most people would want to change, and as it's
still configurable by those who want to and who understand the
implications (by editing tcp.h) I'm happy with the way it is.  

Out of interest, can I ask what problem you want the KEEPALIVE option to
solve?  In most cases people see TCP connections surviving short term
connectivity breakage as a good thing, but sounds like you want to know
(and close connections) if something has gone wrong in the network.

Kieran