[ntp:questions] Question regarding broadcast client

John Zornig j.zornig at uq.edu.au
Mon Oct 20 00:03:41 UTC 2008


On an isolated network, not connected to the internet, I have a  
timeserver appliance connected to GPS which is doing NTP broadcast  
across a UDP one way link to the client system I am trying to  
configure as a broadcast client.

On the client I have a network interface IPaddr:10.9.2.1  Netmask: 
255.255.255.0 Broadcast:10.9.2.255
On the NTP server IPaddr:10.9.2.2 Netmask:255.255.255.0 Broadcast: 
10.9.2.255

Running tcpdump on my client I see regular ntp broadcast packets  
arriving from 10.9.2.2 to addresss:port 10.9.2.255:123

10.9.2.2.123 > 10.9.2.255.123: NTPv4, length 68

On my client I have the following in the ntp.conf file. Note: novolley  
is used as there is no return network path to the timeserver appliance.

broadcastclient novolley
disable auth

The clock on the client is within 2 minutes of the correct time. I run  
ntpd and it does not set the time to match the timeserver.

I run ntpd on the client with -D and I get regular messages coinciding  
with the arrival of the udp packets.
receive: at 1205 10.9.2.1<-10.9.2.2 mode 5 code 6 keyid 00000001 len  
48 mac 20 auth 2
receive: at 1270 10.9.2.1<-10.9.2.2 mode 5 code 6 keyid 00000001 len  
48 mac 20 auth 2
receive: at 1334 10.9.2.1<-10.9.2.2 mode 5 code 6 keyid 00000001 len  
48 mac 20 auth 2
receive: at 1398 10.9.2.1<-10.9.2.2 mode 5 code 6 keyid 00000001 len  
48 mac 20 auth 2
receive: at 1461 10.9.2.1<-10.9.2.2 mode 5 code 6 keyid 00000001 len  
48 mac 20 auth 2

Any suggestions on what I have to do to get ntpd to set the time on my  
client?

The client system is an uptodate Red Hat 5.2 system. The ntp.x86_64  
version installed is 4.2.2p1-8.el5

JZ







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