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DHCP NAK bug in UM3


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Posted (edited) · DHCP NAK bug in UM3

I'm not sure that this is the correct place to post this, but there is a bug in UM3's wifi/networking code that prevents connection to networks due to an error in the DHCP client code.

In particular, if UM3 has an IP address it wishes to use and makes a DHCP registration attempt requesting an address not in the server's DHCP address pool or an address used/reserved for another machine, the DHCP server responds with a DHCPNAK that is - somehow - not only not recognized by UM3, but also interpreted as an all-ok signal. UM3 keeps its old address and thinks it is on the network.

Another bug is that UM3 does not expire DHCP leases. A few days later, UM3 is still refusing to forget about the incorrect address.

Here is the exchange from the server's DHCP logs:

EDIT - your forum software is blocking the log because it contains IP addresses; I am forced to upload as a picture instead:


Edited by Guest
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Posted · DHCP NAK bug in UM3

Thanks for reporting this! I had the odd suspicion something was wrong with the dhcp, but we could never "nail" it.

I'll put up another mark on the network setup problems list.

Note, the current network configuration is provided by connman: https://01.org/connman

So this bug is a direct result of a bug in there.

And I can tell you, we are far from happy about connman. This DHCP bug is one of the many problems with it, and we are planning to replace it with a more standard linux solution. (DNS problems, Wifi connecting problems, not detecting wifi hardware are just a few others to name) All difficult to debug due to connman being one single big entity.

Initially it looked like a good fit, as it did everything we needed. But the amount of problems we are having with it are now overshadowing the positive.

As a workaround, switching the configuration to wifi and back to wired might cause the dhcp client to forget about its lease. But I'm not sure.

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    Posted · DHCP NAK bug in UM3

    Hello mqdusi,

    I see you are trying to connect via wifi. Can you check if this also happens on the LAN connection? Additionally, what DHCP server are you using and would it be possible to post your dhcp config? The forum will likley refuse it, but you could use paste.debian.net maybe?

    If I understand correctly, you first had configuration A on your network (either pool A range of IP address or a dynamic pool); then modified your DHCP server config to force this mac address into a different pool (which results in sending out a NACK on the old request and sends out an OFFER on the new pool), right?

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