[lwip-users] Not getting responses to some ARP requests

[Ben Bobbitt]

I’m seeing an odd problem with lwip (1.2) in which the system uses DHCP and gets an IP, and then it will respond to ARP queries from my laptop running netcat, but it fails to respond to other ARP queries.  The only difference that I can see in Wireshark ( other than the source IP of course ) is the packet size of the ARP request (60 bytes, vs 42 bytes from netcat).   Mine is a UDP application that is simply listening on a port.   

 

I’ve stepped through the code and it appears that the system recognizes the ARP request and calls the function to send a reply  - netif->linkoutput(netif, p);   – but nothing shows up on the wire.  And it works with ARP replies to other requests, which is what has me confused.  I can follow this attempt with a transmit ( with a preceding ARP request ) from netcat, and it responds just fine.   

 

I’ll add that the system that is not getting responses is actually another lwip based processor generating the ARP request.   It seems to be adding a ‘trailer’ of zeros to the request.  

 

The etharp.c module is unmodified from the software framework provided by Atmel for the AVR32 processors.    

 

Does anyone know what I should check as far as configuration options that might be affecting this?    

 

Thanks

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