[Dnsmasq-discuss] Failure to respond to DHCPDISCOVER messages after changed time on router

[John Knight]

Hi,


We discovered that a change in the router's time via NTP will cause dnsmasq to stop answering DHCPDISCOVER.  In the wan.cap, NTP server gives an earlier time to the DUT and cause the dhcp server to stop working (ie. Answering DHCPDISCOVER)

Our DUT's time is Aug 5, 2015 16:19:22.575786000, but NTP server provides Aug 5, 2015 16:00:19.588536000 which is about 19 mins before the DUT's time. Thus the dhcp server stop to work until 19mins later. During this 19 minute time period, dnsmasq does NOT answer dhcpdiscover or give out IP leases. After 19 minutes has expired, we see dnsmasq come back to life and begin answering dhcpdiscover messages again.

I realize that this is an abnormal scenario, but we need to safeguard against this kind of failure.  It is showing up in our testing.  One thought on preventing this would be to in effect do a lease renew after the time has changed on the router.  I am not sure how to cause dnsmasq to refresh all of it's leases?  Or should we be more forceful and force expiration of the leases and restart dnsmasq?  Any suggestions on how to best handle this scenario?

One concern we have too is security.  If the NTP messages are hijacked and the time is changed, it could cause dnsmasq to stop functioning thus affecting the router's users.  So, I think its necessary that we address this.  Hopefully someone has some recommendations on how to deal with this.

Regards,  John







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