[lwip-users] Strange ARP behaviour

[FreeRTOS Info]

Hi,

I have lwIP running on a small ARM7 using FreeRTOS.org.  Everything is
running well but I have one unexplained behaviour that only exists when
using one particular router.

I have the ARM7 board and my laptop plugging into a 10BaseT hub.  The hub is
plugged into an autoswitching all singing all dancing Cisco router.

I can ping the ARM7 from my laptop through the local hub so it is
operational.  I cannot ping the ARM7 from any other computer plugged into
the other side of the big Cisco router.

Now here is the odd thing.

1) http://www.FreeRTOS.org/temp/arp2win2k.gif shows me pinging my laptop
from another computer on the other side of the Cisco.  You will see the ARP
goes in, a response is generated, and the ping messages start as expected.

2) http://www.FreeRTOS.org/temp/arp2sam7x.gif shows me pinging the ARM7 from
another machine on the network, again the other side of the Cisco.  You will
see that the ARP messages successfully goes through the Cisco, through the
hub, and is received by the ARM7.  The ARM7 generates a response, the
response goes onto the wire because I can sniff it ok from my laptop, but
somehow is not accepted.  Rather than the ping's starting to come in, the
ARP's are just repeated.

Comparing the two traces does not show any clues (to me anyway) as they look
to be the same other than the different MAC and IP addresses.

Can anybody shed any light on why the ARP responses are not reaching their
destination, or why they are being rejected.  Other switches I have tried
have been happy with all connection parameters (speed, etc.).

Thanks for any suggestions.

Regards,
Richard.

http://www.FreeRTOS.org