[Devel] tcp keepalive question

[Klaus Darilion]

Juha Heinanen wrote:
> i did some tcp tests using nokia N80 phone and it turned out that if
> there was no other activity, it kept on sending 4 byte tcp messages
> every 20 minutes, which wireshark reported as "continuation" messages.
> they wre enough to keep linux iptables nat binding open.  i have been
> told that it is possible to configure the keepalive interval in N80
> using some special means.
> 
>  > I think there was a discussion on sip-implementors discussing this topic
>  > and the conclusion was, that this is different an every OS and often not
>  > configurable (or least only per system, not per application/connection).
>  > Thus it is to unreliable.
> 
> my understanding is tcp keepalive options are supported in linux are
> they are configurable per tcp session.

Some references:
http://libkeepalive.sourceforge.net/docs/TCP-Keepalive-HOWTO discusses 
keep-alive in general

I have not found an authoritative documentation about the "per TCP 
connection" settings, but I looks like it is done with socket options:

from kernel's (2.6) include/linux/tcp.h

/* TCP socket options */
#define TCP_KEEPIDLE            4       /* Start keeplives after this 
period */
#define TCP_KEEPINTVL           5       /* Interval between keepalives */
#define TCP_KEEPCNT             6       /* Number of keepalives before 
death */


regards
klaus


-- 
Klaus Darilion
nic.at