[lug] Xinetd Based Services

chris fool at dfw.net
Tue Jan 29 10:52:35 MST 2002

On Tue, Jan 29, 2002 at 05:11:22AM -0700, SoloCDM wrote:
> What do the following xinetd based services provide?
> chargen: off
> chargen-udp: off


a stream of characters to the connecting process.  
only of use for debugging purposes as far as i know (perhaps your ppp
connection doesn't handle escaping the character 'a' properly--this would
be a quick way to tell what isn't making it thru, for the printable ascii
characters anyway.
turned off by default due to its extremely bandwidth consumptive nature
(it was a player in a denial of service attack in recent memory) and
extremely infrequent usefulness.

> daytime: off
> daytime-udp: off

a human readable version of the current time on the server.  i personally
leave this one enabled on fileservers so i can very that clocks are in sync
(ntpd fails occasionally on some hosts i use) with some the server (mostly,
i only care about time in relation to the fileserver and logserver), ie:
date ; telnet server daytime

> echo: off
> echo-udp: off

an echo of whatever you give it.  also of minimal actual usefulness except
in aforementioned denial of service attack (string together chargen on one
host and echo on another and you get a saturated network between the
two, quickly).

> time: off
> time-udp: off

computer readable version of the current time on the server.  applications
like "rdate(1)" use it to query the time.
you can see what these services do with a telnet client--enable them and
"telnet host servicename" (ie telnet localhost daytime) to see their
output.  recall, when you hit chargen especially, that the escape key
for the telnet client is usually control-[

> Also, do the above services have anything to do with telnet or ftp?

well, in the sense that you can access the tcp versions with a telnet
client, yes.  but in the way i suspect you meant it (ie do they allow
access to some potentially vulnerable part of the system like telnetd
or ftpd), no.  and no services on a machine except possibly identd affect
outgoing telnet or ftp from that machine.

hope that helps.

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