Re: [lwip-users] Communication between different subnets

[hellish]

Thanks for your reply!
After some serious debugging today I found that the real problem lies in my
FTP-related code. I thought something was wrong with lwip because of the
somewhat misleading comment in the lwip source code and the fact that
wireshark running on my PC didn't capture any packets.

Lesson learned:
1. When sending packets to non-local subnets, during the lookup stage lwip
changes the destination IP to that of the gateway in order to find gateway's
MAC address. The destination IP of the packet itself remains unchanged.

2. Wireshark can't capture packets that are neither sent or received by the
host.

Thanks again for your detailed suggestions, Kieran! 


Kieran Mansley wrote:
> 
> On Tue, 2010-09-14 at 05:32 -0700, hellish wrote:
>> Thanks for clearing up the IP destination confusion! Sure, I'll use
>> wireshark
>> to capture some packets tomorrow.
>> Then again, I remember doing this yesterday and wireshark didn't see any
>> packet (from my board to FTP server), hmm....
> 
> Where were you running wireshark?  If on your PC you wouldn't expect it
> to see packets as they're not going to or from it.  If you can configure
> your switch to do port mirroring you might be able to get them that way.
> Alternatively get the packet capture by running it on something
> mid-stream (e.g. the gateway).  That probably isn't an option on your
> live school network, so you might need to set up a little network of
> your own to reproduce it.
> 
> If the traffic level is very low and you can get the console output from
> your board you might have luck just using the debug statements in lwIP
> to dump details of the packets sent and received.  This is potentially
> easy to try, though much less useful than a full packet capture.
> 
> Kieran
> 
> 
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