Subject: multicast NTP sends pkts with class-D source address?
To: None <>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: tech-net
Date: 02/10/1999 18:04:53
I'm configuring xntpd-3.93c to use multicast on a single subnet.

I have a netbsd 1.3H (i386, old current) running as a stratum-3
multicast server. 

The dratted NetBSD (1.3H, yes its old) box answers unicast chimes sent
by its multicast clients properly, except that the source address
comes out as a multicast address:

7:25:34.277891 cup burner ip 90: NTP.MCAST.NET.ntp > Burner.DSG.Stanford.EDU.ntp: v3 sym_act strat 2 poll 10 prec -18 dist 0.002990 disp 0.152404 ref MightyDog.Stanford.EDU@3127685089.271494865 orig 3127685114.088747411 rec +0.025272933 xmt +20.189020723 (ttl 64, id 56545)

Now, rfc-1112 says all hosts should silently drop such packets.
so conforming Linux boxes ignore these.

rfc-1112 also says that, if unspecified, the src address shouldbe the
address of some outgoing interface.  My guess is, xntpd is using a
socket on which it's bound to, but that's just a guess
(ktrace -d doent show anything more useful than a sendto()).
I'll try this tomorrow on -current.

Meanwhile, has anyone else seen this?