[SLUG] Re: TCP keepalives

[Angus Lees <gusl@nospam.cse.unsw.edu.au>]

On Wed, Jun 28, 2000 at 08:32:18AM +1000, Howard Lowndes wrote:
> I have looked around at keepalives and found some interesting parameters
> in /proc/sys/net/ipv4:
> /proc/sys/net/ipv4/tcp_keepalive_probes
> /proc/sys/net/ipv4/tcp_keepalive_time
> /proc/sys/net/ipv4/tcp_max_ka_probes                                                            
> 
> The default values are respectively 9, 7200, 5 which I read as being 5
> probes sent every 2 hours, and when a total of 9 cycles has received no
> response then the connection is determined to be down.
> 
> This means that it could take up to 18 hours to identify the loss of
> connection.

tcp(7):

      tcp_keepalive_probes
              Maximum TCP keep-alive probes to send before giving
              up. Keep-alives are only sent when the SO_KEEPALIVE
              socket option is enabled.

       tcp_keepalive_time
              The number of seconds after no data has been trans
              mitted  before  a keep-alive will be sent on a con
              nection.  The default is 10800 seconds (3 hours).

       tcp_max_ka_probes
              How many keep-alive probes are sent per slow  timer
              run.  To  prevent  bursts, this value should not be
              set too high.

so no, it will give up after keepalive_time + keepalive_probes *
resend timeout (which is presumably fairly small). ie: close to
keepalive_time


-- 
 - Gus
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