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Trouble with DHCP in RTCS

Question asked by christian333 on Sep 18, 2015
Latest reply on Oct 13, 2015 by Carlos_Musich


we observe some problem with RTCS of MQX regarding DHCP renewal (using ipcfg task).


When unplugging and re-plugging the network connector of our device running MQX/RTCS in DHCP mode, everything works fine. First the device uses settings for network A (IP, netmask, gw, dns). After replugging it uses settings of Network B.


But consider the following scenario:

The device is connected to a switch, which in turn is connected to a network offering DHCP (network "A"). Certainly the device wouldn't recognize immediately that something changed when the switch is plugged to another network ("B"), but the device itself stays connected to the switch during that time. But, when the device tries to renew its DHCP lease, it should get a NACK and then a new lease shoul be received, this time from the other network (B). This in fact works as expected, but with the exception of the DNS. IP, netmask and gateway will be set to network B's settings, but DNS will stay unchanged, as received before from network A.


This usecase is highly relevant to us, because we produce devices that are built into installation cabinets of buildings and cannot simply be rebooted. So, if someone decides to change his DSL router for example, after some time the devices installed in the cabinet must resume correct operation. Note that for this reason we set the maximum DHCP lease time to some short value (maybe 10 min).


We had fixed this bug in RTCS of MQX 4.0.x, but in the latest RTCS LWDNS is no longer there, so the fix does not work any more.


Does anybody know how to fix this in RTCS


Thanks a lot in advance and kind regards,