We have a system that uses ntpd to synchronize the system clock. We
allow the user to run ntpd in polling mode with a user-specified set of
servers, or in broadcast mode, accepting any broadcast NTP messages
received.
This used to work fine with ntpd 4.2.4p7. Since upgrading to 4.2.6p5,
polling mode continues to work fine but broadcast mode does not work at
all--ntpd never sees any broadcast messages.
The reason seems to be that ntpd 4.2.6p4 tries to initialize the
broadcast interface before initializing its list of available
interfaces. Here is a simple invocation of ntpd that exhibits the
problem. Note the message about "no broadcast interfaces available" on
the seventh line of output below.
$ ntpd -4 -b -D2 -c /dev/null
ntpd [email protected] Fri Apr 19 01:23:45 UTC 2013 (1)
24 Apr 23:58:35 ntpd[17867]: set_process_priority: Leave priority alone:
priority_done is <2>
24 Apr 23:58:35 ntpd[17867]: proto: precision = 5.380 usec
loop_config: item 1 freq 0.000000
event at 0 0.0.0.0 c01d 0d kern kernel time sync enabled
proto_config: code 1 value 1 dvalue 0.000000
24 Apr 23:58:35 ntpd[17867]: Unable to listen for broadcasts, no broadcast
interfaces available
24 Apr 23:58:35 ntpd[17867]: line 1999510120 column 0 syntax error,
unexpected $end
Finished Parsing!!
create_sockets(123)
24 Apr 23:58:35 ntpd[17867]: ntp_io: estimated max descriptors: 1024,
initial socket boundary: 16
24 Apr 23:58:35 ntpd[17867]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
created interface #0: fd=16, bfd=-1, name=v4wildcard, flags=0x89,
ifindex=0, sin=0.0.0.0, bcast=0.0.0.0, mask=255.255.255.255, Disabled:
create_interface(127.0.0.1#123)
24 Apr 23:58:35 ntpd[17867]: Listen normally on 1 lo 127.0.0.1 UDP 123
restrict: op 1 addr 127.0.0.1 mask 255.255.255.255 mflags 00003000 flags
00000001
created interface #1: fd=17, bfd=-1, name=lo, flags=0x5, ifindex=0,
sin=127.0.0.1, mask=255.0.0.0, Enabled:
create_interface(10.10.143.200#123)
24 Apr 23:58:35 ntpd[17867]: Listen normally on 2 eth0 10.10.143.200 UDP 123
restrict: op 1 addr 10.10.143.200 mask 255.255.255.255 mflags 00003000
flags 00000001
created interface #2: fd=18, bfd=-1, name=eth0, flags=0x19, ifindex=0,
sin=10.10.143.200, bcast=10.10.143.255, mask=255.255.255.0, Enabled:
create_interface(10.27.50.174#123)
24 Apr 23:58:35 ntpd[17867]: Listen normally on 3 remote 10.27.50.174 UDP
123
restrict: op 1 addr 10.27.50.174 mask 255.255.255.255 mflags 00003000 flags
00000001
created interface #3: fd=19, bfd=-1, name=remote, flags=0x19, ifindex=0,
sin=10.27.50.174, bcast=10.27.50.255, mask=255.255.255.0, Enabled:
24 Apr 23:58:35 ntpd[17867]: peers refreshed
create_sockets: Total interfaces = 4
24 Apr 23:58:35 ntpd[17867]: Listening on routing socket on fd #20 for
interface updates
auth_setkey: key 65535 type 4 len 4 6ee30717
event at 0 0.0.0.0 c016 06 restart
loop_config: item 2 freq 1000000000.000000
event at 0 0.0.0.0 c012 02 freq_set kernel 0.000 PPM
local_clock: mu 0 state 1 poll 3 count 0
event at 0 0.0.0.0 c011 01 freq_not_set
auth_agekeys: at 1 keys 1 expired 0
timer: interface update
After waiting long enough for a broadcast message to have been sent by
ntpd running on another host,
$ ntpq -crv
receive: at 96 127.0.0.1<-127.0.0.1 flags 5 restrict 000
sendpkt(17, dst=127.0.0.1, src=127.0.0.1, ttl=-6, len=372)
associd=0 status=c011 leap_alarm, sync_unspec, 1 event, freq_not_set,
version="ntpd [email protected] Fri Apr 19 01:23:45 UTC 2013 (1)",
processor="mips64", system="Linux/3.4.34", leap=11, stratum=16,
precision=-17, rootdelay=0.000, rootdisp=1.440, refid=INIT,
reftime=00000000.00000000 Thu, Feb 7 2036 6:28:16.000,
clock=d522f08b.f70b1c35 Thu, Apr 25 2013 0:00:11.965, peer=0, tc=3,
mintc=3, offset=0.000, frequency=0.000, sys_jitter=0.000,
clk_jitter=0.008, clk_wander=0.000
I looked at the source code for both versions of ntpd and saw that in
4.2.4p7, the list of interfaces was initialized by the following cascade
of function calls,
ntpdmain() --> init_io() --> create_sockets()
In 4.2.6p4, however, most of the contents of the function init_io() have
been stripped out, including the call to create_sockets(). In 4.2.6p4,
create_sockets() is not called until later, after the attempt to create
the broadcast interface.
Is ntpd 4.2.6p4 really broken w.r.t. receiving broadcasts, or do we have
something configured incorrectly?
Regards,
Gary
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