Re: tcp_keepalive_intvl vs tcp_keepalive_time?

Re: tcp_keepalive_intvl vs tcp_keepalive_time?

[Nivedita Singhvi]

> Would someone be kind enough to explain the difference between
> tcp_keepalive_intvl and tcp_keepalive_time?
> Documentation/filesystems/proc.txt says tcp_keepalive_time is the
interval
> between sending keepalive probes, but doesn't mention
tcp_keepalive_intvl...

tcp starts a keepalive timer for each connection. if the connection is idle
for tcp_keepalive_time seconds, it starts sending probes to the other end.
It sends a maximum of tcp_keepalive_probes each tcp_keepalive_intvl
seconds apart, and if the other end hasnt responded by then, it drops the
connection.

default values:

tcp_keepalive_intvl = 75 seconds
tcp_keepalive_probes = 9
tcp_keepalive_time = 7200 seconds (2 hours)

> The problem I'm trying to track down is ssh connections where the
connection
> times out but the session doesn't go away until a key is pressed.  (I.E.
> blocking reads don't notice the connection going down underneath them,
not
> even if left overnight.)

not clear from the info here whats happening in your case...
(stats?)

> Rob

thanks,
Nivedita

[DOC PATCH] Re: tcp_keepalive_intvl vs tcp_keepalive_time?

[Rob Landley]

On Saturday 09 February 2002 11:40 pm, Nivedita Singhvi wrote:
> > Would someone be kind enough to explain the difference between
> > tcp_keepalive_intvl and tcp_keepalive_time?
> > Documentation/filesystems/proc.txt says tcp_keepalive_time is the
>
> interval
>
> > between sending keepalive probes, but doesn't mention
>
> tcp_keepalive_intvl...
>
> tcp starts a keepalive timer for each connection. if the connection is idle
> for tcp_keepalive_time seconds, it starts sending probes to the other end.
> It sends a maximum of tcp_keepalive_probes each tcp_keepalive_intvl
> seconds apart, and if the other end hasnt responded by then, it drops the
> connection.

Thanks.

Patch to proc.txt:

--- linux/Documentation/filesystems/proc.txt    Wed Nov  7 17:39:36 2001
+++ linux/Documentation/filesystems/proc.bak    Sun Feb 10 02:46:55 2002
@@ -1421,8 +1421,14 @@
 tcp_keepalive_time
 ------------------

-How often  TCP  sends out keep alive messages, when keep alive is enabled. The
-default is 2 hours.
+Number of seconds a connection must remain inactive before sending the first
+keep alive probe, when keep alive is enabled. The default is 7200 (2 hours).
+
+tcp_keepalive_intvl
+-------------------
+
+Number of seconds a keep alive probe must go unanswered before sending
+another one.

 tcp_syn_retries
 ---------------




> not clear from the info here whats happening in your case...
> (stats?)

SuSE is being annoying in a way Red Hat wasn't.  The box has a 2.4.6
kernel on it, I'll probably upgrade that before pursuing this much further
(which I won't be in a position to do until I physically get back to
Austin...)  Since I've been playing with Linux From Scratch recently, I 
ight throw the system I've put together on there so I at least know what
the heck it's all doing. :)

What kind of packets are keepalive packets, by the way?  (I don't think
the firewall rules are filtering them out, but I can't be sure.)

> > Rob
>
> thanks,
> Nivedita

Rob again. :)

tcp_keepalive_intvl vs tcp_keepalive_time?

[Rob Landley]

Would someone be kind enough to explain the difference between 
tcp_keepalive_intvl and tcp_keepalive_time?  
Documentation/filesystems/proc.txt says tcp_keepalive_time is the interval 
between sending keepalive probes, but doesn't mention tcp_keepalive_intvl...

A quick grep through the source code says tcp_keepalive_intvl wanders through 
keepalive_intv_when which is used in tcp_keepalive_time in a way that sort of 
implies it's the timeout between keapalive packets.  So what's 
tcp_keepalive_time?

The problem I'm trying to track down is ssh connections where the connection 
times out but the session doesn't go away until a key is pressed.  (I.E. 
blocking reads don't notice the connection going down underneath them, not 
even if left overnight.)

It's kind of frustrating, actually...

Rob