Re: [lwip-users] dhcp_release_and_stop() clears the assigned IP address

[R. Diez]

> Ehrm, how do you reach the device for commissioning? Via DHCP or via 
> fallback-IP? ;-)
>
> So if the user has to enter an IP address, why use DHCP?

The devices come with a default IP address. This is how most Internet routers come preconfigured. During commissioning, you connect the new 
device directly to your PC, or to a trusted local network. You then configure all options you need (DHCP yes/no, fallback IP, security...), 
and afterwards you connect it to the main network. That is standard practice. Usually, you do not want to connect a device to your main 
network before you have set up at least security.

I do not think that a proprietary solution based on broadcasts is any better. What kind of broadcasts are you using? Are they able to cross 
routers? How you properly secure it, so that nobody can send a broadcast that resets all your device IP addresses, or sniff the password 
from the next broadcast? If there are good answers, then it would be something valuable to add to the lwIP suite, because this kind of 
problem is common across most IP devices.


> > Even if all devices have the same fall-back IP, that does not really matter, as 
> > long as it is on a different subnet
> or it is a reserved IP for that purpose.
>
> It does. You'll get bogus result trying to reach such devices.
>
>  >Networks should still operate correctly if a client device IP is duplicated.
>
> Network yes. IP communication won't.


That is fine. If the DHCP server goes away and your leases expire, I believe that your devices are required by the standard to stop using 
those leases. That would break communications too. Let's face it: if your system relies on DHCP, and your DHCP server goes down, your 
network is not going to work properly. At the very least, devices that restart will not get a proper IP address. AutoIP is not going to help 
you. If it did, then you did not actually need DHCP for your network in the first place.


> If the DHCP server is down, and the devices need it, you have bigger problems anyway. The fall-back IP is mainly designed so that you can 
> easily isolate a device and access it with a minimum of fuss.
>
> That's what AutoIP was invented for...

I am not familiar with AutoIP in lwIP yet, but that looks interesting. Say you have a local network with 1 Linux PC, 1 Windows PC and 1 
small device. Is there an easy why to discover the small AutoIP device from Linux and from Windows? I do not want my users to have to resort 
to Wireshark or the like.

Last time I looked, I could not find a proper network discovery protocol like zeroconf or Bonjour in lwIP. Is there anything new in this 
respect?

Regards,
  rdiez