telnetd keepalive every 15 minutes

telnetd keepalive every 15 minutes

Post by john » Wed, 08 Oct 1997 04:00:00



telnetd is sending something to idle telnet clients every
15 minutes... how do I make it stop?

details:

We are running some linux systems installed with
redhat version 4.0 (NetKit-B-0.06). We use telnet over
isdn lines between these machines. We've found that
if you leave a telnet client connected (but not used)
to the remote system, there is a packet volley from
the server to the client and back about every 15 minutes.
This brings up our long distance isdn lines when people
leave telnet sessions up every 15 minutes and gets expensive
after while.

Was wondering what these packets are and more importantly,
how to get them to stop!

thanks,
        john

Below is some output from tcpdump (visi-central-alt is the client
and 192.100.2.2 is the server):

02:08:21.119795 192.100.2.2.telnet > visi-central-alt.1705: . ack 432
win
31744
02:08:26.609795 visi-central-alt.1705 > 192.100.2.2.telnet: . ack 313719
win 14335
02:23:26.609795 192.100.2.2.telnet > visi-central-alt.1705: . ack 432
win
31744
02:23:31.999795 visi-central-alt.1705 > 192.100.2.2.telnet: . ack 313719
win 14335
02:38:31.999795 192.100.2.2.telnet > visi-central-alt.1705: . ack 432
win
31744
02:38:37.369795 visi-central-alt.1705 > 192.100.2.2.telnet: . ack 313719
win 14335

 
 
 

telnetd keepalive every 15 minutes

Post by Georg v.Zezschwit » Wed, 08 Oct 1997 04:00:00



: telnetd is sending something to idle telnet clients every
: 15 minutes... how do I make it stop?

I'm afraid there is no way apart from recompiling telnetd or telnet.
You should look for an ioctl-call somewhere in the sources, and
remove a flag named *KEEP_ALIVE.

This flag specifies that the connection is checked from time to time.

If you remove it, your problem should be solved. However: It's a
feature, not a bug, and if you change this, you might wan't to
check from time to time if some telnetd's are still running from
some broken connections.

Bye,

Georg

 
 
 

telnetd keepalive every 15 minutes

Post by Ian Rawlin » Thu, 09 Oct 1997 04:00:00




Quote:> telnetd is sending something to idle telnet clients every
> 15 minutes... how do I make it stop?

It's *y simple, you go to the command-line prompt and type "man
in.telnetd" and you'll find the answer a page or two down from the
top. You're the second person recently who didn't even try a cursory
read of the manual before posting a message to news. You're not at
school now you know!

--
Ian Rawlings - ** decode anti-spam address to contact me **

 
 
 

telnetd keepalive every 15 minutes

Post by Paul Slootm » Fri, 10 Oct 1997 04:00:00





>> telnetd is sending something to idle telnet clients every
>> 15 minutes... how do I make it stop?

>It's *y simple, you go to the command-line prompt and type "man
>in.telnetd" and you'll find the answer a page or two down from the
>top. You're the second person recently who didn't even try a cursory
>read of the manual before posting a message to news. You're not at
>school now you know!

Calm down. Recent versions of the in.telnetd manpage shows that, but
e.g. on my workstation it doesn't. My system was installed about 2 years
ago, and has been upgraded here and there in parts, but those manpages
and in.telnetd haven't been. (Originally Slackware 2.x).

However, "strings /usr/sbin/in.telnetd" shows that the usage string
included the "-n" option, so apparently the manpage doesn't agree with
the executable.

Anyway, for those manpage-challenged persons, add the "-n" flag to the
in.telnetd invocation, that should help.

--
Paul Slootman

 
 
 

telnetd keepalive every 15 minutes

Post by john » Mon, 13 Oct 1997 04:00:00


Yeah '-n' works, thanks Paul.

And yes, Ian, I *y-well did read the man page before
posting. The telnetd man page distributed with redhat 4.0
makes absolutly no mention of "-n".

-john





> >> telnetd is sending something to idle telnet clients every
> >> 15 minutes... how do I make it stop?

> >It's *y simple, you go to the command-line prompt and type "man
> >in.telnetd" and you'll find the answer a page or two down from the
> >top. You're the second person recently who didn't even try a cursory
> >read of the manual before posting a message to news. You're not at
> >school now you know!

> Calm down. Recent versions of the in.telnetd manpage shows that, but
> e.g. on my workstation it doesn't. My system was installed about 2 years
> ago, and has been upgraded here and there in parts, but those manpages
> and in.telnetd haven't been. (Originally Slackware 2.x).

> However, "strings /usr/sbin/in.telnetd" shows that the usage string
> included the "-n" option, so apparently the manpage doesn't agree with
> the executable.

> Anyway, for those manpage-challenged persons, add the "-n" flag to the
> in.telnetd invocation, that should help.

> --
> Paul Slootman

 
 
 

telnetd keepalive every 15 minutes

Post by Ian Rawlin » Wed, 15 Oct 1997 04:00:00




Quote:> And yes, Ian, I *y-well did read the man page before
> posting. The telnetd man page distributed with redhat 4.0
> makes absolutly no mention of "-n".

Sorry, I get a bit irate at times... I think few people can be
complacent about the number of times people post to news before even
looking for the info themselves. There's the man pages, howtos,
DejaNews, the web, *then* usenet, that's the way I do it.

Usually.

--
Ian Rawlings - ** decode anti-spam address to contact me **