[ntp:questions] NTP is deleting the interface on lease expiry from DHCP Server

Martin Burnicki martin.burnicki at burnicki.net
Wed Feb 8 10:13:22 UTC 2017


Hi,

akash saxena wrote:
> Hi all,
> 
> I am facing the issue with ntpd.
> My ntpd is listening the ip provided by the DHCP Server.
> It looks for the sync in 10 seconds but before 10 seconds DHCP lease expiry
> happened and
> ntpd started deleting the interface on which it was priviously listening.
> 
> and this stops the communication between my client and NTP server.
> 
> *Refer the logs:*
> 
>  ntpd[1686]: proto: precision = 0.989 usec (-20)
>  ntpd[1686]: Listen and drop on 0 v6wildcard [::]:123
>  ntpd[1686]: Listen and drop on 1 v4wildcard 0.0.0.0:123
>  ntpd[1686]: Listen normally on 2 lo 127.0.0.1:123
>  ntpd[1686]: Listen normally on 3 eth1 172.19.61.236:123
>  ntpd[1686]: Listen normally on 4 lo [::1]:123
>  ntpd[1686]: Listen normally on 5 eth1 [fe80::ee8c:a2ff:fe31:743d%4]:123
>  ntpd[1686]: Listening on routing socket on fd #22 for interface updates
>  ntpd[1686]: *Deleting interface #3 eth1*, 172.19.61.236#123, interface
> stats: received=1, sent=1, dropped=1, active_time=5 secs
>  ntpd[1686]: 104.154.107.129 local addr 172.19.61.236 -> <null>
>  ntpd[1686]: 146.148.32.216 local addr 172.19.61.236 -> <null>
>  ntpd[1686]: Listen normally on 6 eth1 172.19.61.236:123
>  ntpd[1686]: new interface(s) found: waking up resolver
> 
> 
> *Can anyone please explain me what is this Deleting the interface by ntpd.*

If I remember correctly then ntpd listens on the routing/netlink socket,
so it receives a notice from the kernel whenever an interface appears or
disappears.

I'd even *expect* that ntpd stops trying to use an interface which has
disappeared.

Sounds like your DHCP server provides only a short lease time, but then
is offline for longer than the lease time, so the lease can't be
refreshed, expires, and thus the kernel shuts down the interface.

Martin



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