Re: [lwip-users] LPC1769 ethernet problem

[Fotis Panagiotopoulos]

Well, it seems I narrowed down the problem.

As I see in wireshark, when my microcontroller sends an ARP request about my gateway it does not receive any response. It continues sending the same request for about 30 secs (the time I wasn't seeing any UDP traffic), and then it starts sending the UDP packet.

Two odd things are:
the duration of the failed ARP requests is not constant, may be 10 to 50 secs.

it never gets any response from the router on the ARP request.

So practically I believe it is something about the ARP, that LWIP cannot find the address of the router, while it has no problems, resolving the address of the other local computers. Any hints?

Fotis Panagiotopoulos

--

AMCO S.A.

25 Amfiaraou st. PO 10442, Athens, Greece
Tel: +30 210 5907000 ext. -34 | Fax: +30 210 5912711
e-mail: address@hidden | web: http://www.amco.gr

On Fri, Aug 12, 2016 at 2:31 PM, Fotis Panagiotopoulos <address@hidden> wrote:

OK I bought a managed switch, so I can now monitor the traffic on my network correctly. I set up the port mirroring function, to forward all traffic from the ethernet port the uC is connected, to the port that my PC is connected. I started wireshark but the problems persist.

First my code starts LWIP, the MAC controller and sets a static IP with no problems.

Then my code enters a loop and tries a DNS query. Here the fancy staff starts. The first calls to dns_gethostbyname do not produce any traffic (yes I properly wait for the callback function to check the result, before the next call). After continuing to call this function, I finally see traffic in wireshark after app. 30 seconds. I can see an apparently normal DNS packet being sent but there is no response from the server.

Then I tried to provide directly the IP of the server, (effectively I stopped using the DNS functionality), and tried to directly connect to an NTP server (using UDP of course). Again the same sumptoms. udp_send returns ERR_OK, but no traffic at the network. After app. 30 seconds I see the packets being sent but again absolutelly no response from the server.

Keep in mind that I can ping my device normally, that I tried many servers (which are proved to work, testing from my PC), that I double checked our firewall (and that everything works OK from my PC).

Also note that these problems exist only when I try to connect to an external (to my LAN) server. Trying to connect to a local server works normally.

Fotis Panagiotopoulos

--

AMCO S.A.

25 Amfiaraou st. PO 10442, Athens, Greece
Tel: +30 210 5907000 ext. -34 | Fax: +30 210 5912711
e-mail: address@hidden | web: http://www.amco.gr

On Mon, Aug 1, 2016 at 9:22 PM, address@hidden <address@hidden> wrote:

Fotis Panagiotopoulos wrote:

I am asking for the brand/model number of the one that you are successfully using, to search for a new or used one. As you can image buying lots of switches in the hope that randomly one of them will have this functionality, is not an good idea :)

You don't have to buy randomly, just look for a switch that supports "port mirroring". These should be available from around ~100 EUR or USD...

The more professional tool for monitoring would be an ethernet tap, which has two ports that work like a repeater and forwards both RX sides to a 3rd port (e.g. ETH or USB) to monitor via wireshark.

If you want a cheaper solution, grab two network cards for your PC and build your own passive tap (e.g. like this: http://www.securityforrealpeople.com/2014/09/how-to-build-10-network-tap.html). You'll have to monitor every side on its own (using wireshark), but you can mix 2 pcaps into one later if you prefer. Mixing is done via timestamps, so using 2 same cards (which are NOT USB) should give the best results.
(ATTENTION: as this is passive and you attach a 2nd ETH receiver to one cable, using very short cables is recommended - and worked well for me once I tried!)

Simon

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