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Re: [lwip-users] FW: Problem with renewing DHCP after link down/up with

From: simeon.trifonov
Subject: Re: [lwip-users] FW: Problem with renewing DHCP after link down/up with the new LWIP V2.0.2
Date: Tue, 3 Apr 2018 11:43:54 +0300

OK, I have already explanation of my strange problems with the DHCP renew. The problem was, unfortunately, in my code . The stack stores a chained pcbs for all UDP connections. DHCP creates such connection when it is started. But because of my mistake, I brake the chain and I'm losing connection with the pcb, created from the DHCP (the first one that was created after power on). Therefore by renew the stack doesn't find a pcb for port 68. After a small fix in my code all works just fine and it is so simple as it should be.




> -----Original Message-----

> From: lwip-users <lwip-users-bounces+simeon.trifonov=amk-

> address@hidden> On Behalf Of address@hidden

> Sent: Friday, March 30, 2018 4:10 PM

> To: Mailing list for lwIP users <address@hidden>

> Subject: Re: [lwip-users] FW: Problem with renewing DHCP after link

> down/up with the new LWIP V2.0.2


> 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, 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


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