Firewall on Linux-2.0.35 and xntpd

Juha Virtanen (jiivee@hut.fi)
Wed, 19 Aug 1998 11:04:50 +0300

I've setup up a RedHat 5.1 Linux box with Linux-2.0.35 as
filtering firewall with policy reject everything if not defined
otherwise.

I want to use xntpd on that box, so I allow udp traffic from
everywhere from port 123 (ntp) to everywhere to port 123 and
back. This works. (Rule could be more restrictive, but it's not
topic of this message.)

Now xntpd does something weird during startup (in the child
process) and if firewall rules are enabled it emits these
messages to syslog:
Aug 18 14:35:02 fw xntpd[399]: send to NTP server failed: Operation not permitted
This message comes from .../xntpd/ntp_intres.c: function request().

Now, if I disable firewalling rules for that time xntpd starts
up, no problem. After it has started succesfully I may again
enable firewalling rules and xntpd continues to work. Netdate
works all the time.

Xntpd is as found in RedHat-5.1's xntpd3-5.93-2.i386.rpm.
Linux-2.0.35 is compiled from sources.

Which one is broken, xntpd or Linux kernel?

I don't know networking well enough to dig down into this myself.

Regards,
Juha

-- 
<URL:http://www.iki.fi/jiivee/>


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