[lwip-users] Re: [lwip] weird piece of code in etharp since 0.5.3+ ??

[leon . woestenberg]

Hello Martin,

ah yes, of course. This piece of code is used once ip_route() returns
"netif_default",
i.e. the interface where the default gateway is on.

The ARP code then fills in the Ethernet address of the gateway.

OK, everything seems correct. Will add some comments to the code.

Regards,

Leon.



                                                                                
                                                       
                      Martin Glunz                                              
                                                       
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                      Sent by:                 Subject:  Re: [lwip] weird piece 
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                      29-11-2002 11:38                                          
                                                       
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address@hidden wrote:
>
> Hello,
>
> I came across something weird which seems to be in lwIP since 0.5.3 or
so:
>
> etharp.c/etharp_output() contains this piece of code:
>
>   }
>   else {
>     if(!ip_addr_maskcmp(ipaddr, &(netif->ip_addr), &(netif->netmask))) {
>       ipaddr = &(netif->gw);
>     }
>
> It seems to send a packet to the default gateway if its address is not on
> the
> local network.
>
> Now, shouldn't this decision be made in the IP layer _only_? I.e. the
> packet should not be output on this interface in the first place.
>

I've seen this too. It works if there is only one interface, I never
tested more than one interface on my target system.
Problem is that only the mac address of the default gw must be placed
in the packet, the destination IP must be preserved, and inside
etharp.c it seems to be a good place to do so (for a quick hack,
i guess).
I never analyzed the ip_route code, so I can't tell if it is easily
possible to move this code there, but I think it is the right way to
handle the default gw in ip_route.


Martin Glunz


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