Date: Mon, 8 Mar 2010 20:37:49 +1100 From: John Marshall <john.marshall@riverwillow.com.au> To: freebsd-stable@freebsd.org Subject: Re: ntpd multicast TTL Message-ID: <20100308093749.GB963@rwpc12.mby.riverwillow.net.au> In-Reply-To: <hn0jlp$5l4$1@lorvorc.mips.inka.de> References: <hn0jlp$5l4$1@lorvorc.mips.inka.de>
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--gj572EiMnwbLXET9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, 07 Mar 2010, 16:19 +0000, Christian Weisgerber wrote: > ntpd is a convenient source of multicast packets for testing purposes. > When I add >=20 > broadcast 224.0.1.1 >=20 > to my ntp.conf, ntpd sends a multicast packet with TTL 1 every 64 > seconds. Just as expected. However, when I explicitly specify the > TTL as in >=20 > broadcast 224.0.1.1 ttl 1 >=20 > it sends packets with TTL 32. Trying a few other numbers confirms > that it multiplies the specified TTL by 32. That is not expected. > (I also don't recall this happening the last time I tried it, but > that may have been years ago.) >=20 > Is this simply a bug in ntpd? No, it's just that the ntp's server configuration statements don't use their ttl option to specify network ttl value, but as zero-based index into ntp's ttl value array. The default array is as you describe [1,32,64,96,128,160,192,224] but can be overridden by the ttl configuration statement. So the following lines in your ntp.conf would result in your multicast server transmitting packets with ttl=3D4. ttl 2 4 6 8 broadcast 224.0.1.1 ttl 1 I tripped over this last year when experimenting with ntp multicast. I had to resort to the source code to understand what was happening. It is actually documented. <http://www.eecis.udel.edu/~mills/ntp/html/miscopt.html#ttl>; --=20 John Marshall --gj572EiMnwbLXET9 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAkuUxW0ACgkQw/tAaKKahKKAogCfQzQSQtfYYGMzp7wWN00yiW4m +OEAoIZQzlEddVIGdbRRjojpITYg0/tH =exTv -----END PGP SIGNATURE----- --gj572EiMnwbLXET9--
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