Re: [lwip-users] No ARP reply by using two NICs

[Sylvain Rochet]

Hi,

On Tue, Aug 14, 2012 at 03:01:59PM +0200, Stefan Lankes wrote:
> Hi LwIP users,
> 
> I have an ARP problem and I am not sure, if this a problem of LwIP.
> 
> In our academic operating system, we use LwIP 1.4.0 as TCP/IP stack. 
> My test system posses two network devices and each device belongs to 
> its own subnet. I enabled IP forwarding to transfer IP packets between 
> the subnets and it seems to work.
>  
> However, if a member of subnet A broadcasts an ARP request to 
> determine the physical address of a member of subnet B, our system 
> does not forward these broadcasts to subnet B. LwIP drops the requests 
> with the message "ARP request was not for us."
>  
> Is this behavior correct?

With your wanted behavior, a broadcast Ethernet frame sent to a router 
connected to the global IP space would be received by all IP equipments 
connected, which is about billions of systems. And you are considering 
the whole Internet is only made of Ethernet links, which is false. Maybe 
you have to learn the difference between layer 2 and layer 3.

Sylvain

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