Re: [lwip-users] FW: Problem with renewing DHCP after link down/up with the new LWIP V2.0.2

[address@hidden]

On 30.03.2018 13:01, address@hidden wrote:
> I replaced the function dhcp_renew() with dhcp_network_changed(). After
> power on, the dhcp works fine again (the complete log is attached). The
> first strange thing for me is the ARPs that follow. The devices askes who
> has IP address 192.168.5.60, but it is his new address... Is that normal?

Yes. The client checks if the address assigned by the server is really 
unused. This is sometimes called "address collision detection" (ACD) and 
is e.g. required for Ethernet-IP at least... Just yesterday I had a DHCP 
server assigning a duplicate address, where this helps :-)

> The other strange thing is that if I disconnect the Ethernet cable and
> connect it again (in the same network), all things that follow (after line
> 12) are not understandable for me.

The IP checksum of the DHCP ACKs are 0, but that might be checksum 
offloading because you monitor on the host that is running the DHCP 
server? If not, it's correct that lwIP does not get them.

> I seems that my device doesn't receive
> the frames from the DHCP server.

Hmm, looking again, it seems that lwIP just does not receive the answers 
as valid DHCP packets, as it sends an ICMP "port unreachable" as 
response. That's strange... I don't think that's a problem with your 
tunneling thing...

Simon