ntp starts working when restarting arp
Hi.
I had an issue with one of myservers who didnt want to sync its clock using ntp. Prior solving the proplem the ntpq status was as below: Code:
I tried it and it worked for me as well! So as soon i cleared arp table and restarted the ntp everything worked just fine. Thing is that the post was very old and the guy didnt bother to provide further explaination hence i am left with the though "WHY" How could the ntp corelate with the ntp? Why when clearing arp ntp works? Any ideas? |
There are a couple of perhaps interesting places you may want to look at about Address Resolution Protocol (ARP): http://en.wikipedia.org/wiki/Address...ution_Protocol and, maybe, https://supportforums.cisco.com/disc...lear-arp-cache.
Something to know is what ARP does: Quote:
That is, it's local, not external. This suggests a question or two: what does the server you're having a problem with use for DNS service (an external DNS server, BIND, a DNS server on you LAN, a DNS server in your router/switch)? It also suggests perhaps a large time difference between an external time source and your hardware or system clock (when NTP refuses to initialize it generally (but not always) means that your system clock is too far out of time for NTP to use it. Looking at the result of your nptq -p above I note that you do not have a local server defined; I'd suggest that you add one to the server area of your /etc/ntp.conf file: Code:
server 127.127.1.0 # local clock Also, look at your start up for NTPD. Somewhere in the shell program that starts the daemon you should have a line that looks similar to this: Code:
/usr/sbin/ntpd -g You may want to look at your hardware clock time (in the BIOS); the (software) system clock is set from the hardware clock on boot, NTPD synchronizes the system clock while you're running and on shutdown the system clock time is written to the hardware clock. If you've not been synchronized for some period of time your system clock may have drifted enough to more than then panic threshold (1000 seconds) which is subsequently saved to the hardware clock and when you reboot you're not going to get synchronized without the above -g argument. You can set the system time with ntpd: Code:
ntpd -q "Reachable" means that you have a DNS server available so you can Code:
ping -c 5 ntp1.server.de Code:
ping -c 5 0.de.pool.ntp.org Are your server addresses LAN addresses? If so, that explains why clearing the ARP cache got you going; you forced it to go through the ARP process again, ARP has nothing to do with external addresses. So, anyway, that's a long, round about way of getting to what may be your problem. Hope this helps some. |
OK ... so the issue was caused by two main reasons:
1) ntp was configured to operate with IPv6 2) the server for some reason lost its IPv6 gateway hence couldnt communicate to other ntp servers Solved by switching ntpd to operate with ipv4 |
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