[ntp:questions] sendto( Invalid argument

Danny Mayer mayer at gis.net
Sat Aug 13 21:40:36 UTC 2005

Edrusb wrote:
> Dear all,
> The problem I met concerns ntpd when a changes in the network interface
> set occurs.
> My Linux system (on which runs ntpd-2.4.0) has two links to Internet:
> one is permanent (except upon hardware failure), the second is a backup
> modem line.
> Actually the "permanent" link is broken so the dialup modem line is in
> action, and a ppp0 interface goes up and down upon request. If I launch
> ntpd when the link is down, ntpd will never synchronize with peers even 
> when the link comes back short after: it has a wildcard UDP socket 
> opened on port 123 and for each other interfaces that existed when ntpd 
> was launched, it has an UDP interface specific socket on port 123 too 
> (information given by the netstat command). The problem is that when the 
> link goes up then ntpd does not seems using the wildcard socket to try 
> to reach peers and does not create a new UDP interface specific socket 
> for this new interface (ppp0) so peers stay unreachable as reported by 
> ntpdc, even long after the link came back (tried more than 2 hours).
> In the other way, if I launch ntpd when the link is up, it properly
> exchange time information with its peers, but when the link goes down,
> it keeps its UDP interface specific socket opened on ppp0 interface
> while this ppp0 interface is now down. At that time I start having
>     "ntpd[11911]: sendto(x.x.x.x): Invalid argument"
> messages as reported by syslog (with x.x.x.x rotating with all the IP
> address of the configured peers). The worse thing is that when the link
> comes back, ntpd still has his old socket opened, but still are reported
> a lot of "Invalid Socket" messages and of course, ntpd cannot anymore
> synchronize with ntp peers.
> - What is the use of this wildcard UDP socket (it does not seems used)?
> - Why does ntpd uses theses UDP specific interfaces sockets, while the
> configuration file does not specify any interface to listen on or to not
> listen on?
> - How to have ntpd be able to work with a dialup link?

See bug #51. Yes, as Brad says, we will be fixing this, but it's not a 
simple thing to implement so it won't be soon.


> Any help is (very) welcome. :-)
> Regards,
> Denis.
> -- 
> edrusba at free.fr
> remove the a letter in the email above

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