Re: [lwip-users] Sending to a non-local network without default netif set

[HaaCee2]

On 14-11-14 20:27, Simon Goldschmidt [via lwIP] wrote:

HaaCee2 wrote:

> I am not entirely familiar with the ideas behind LwIP. But sourcebased
> routing is very much in line with rfc1122 (ip for hosts). I quote:
>
>> Under the Strong ES model, the route computation for an outgoing datagram
>> is the mapping:
>>
>>                           route(src IP addr, dest IP addr, TOS) -> gateway
>>
>> Here the source address is included as a parameter in order to select a
>> gateway that is directly reachable on the corresponding physical
>> interface. Note that this model logically requires that in general there
>> be at least one default gateway, and preferably multiple defaults, for
>> each IP source address.

Well, that excerpt is one of 2 possibilities in the RFC. The other
possibility is to do like lwIP does. I admit though that it looks kind
of strange sending packets with IP address A to the interface B just
because you have a matching destination gateway on that netif...

    You are correct that it is only 1 of the 2 possibilities, and as
    indicated I am not familiar with the design of lwIP. So it's a
    perfectly valid choice NOT to support sourcebased routing.
>       By now, I'm tempted to add source-based routing as an option,
>       although I 
>       expect people using lwIP wih more than one interface being only a
>       small 
>       percentage...
>       
>     
    I beg to differ.... 
    In my opinion the best approach to deal with vlans is to have
    multiple interfaces and then I think one is required to do
    sourcebased routing. Otherwise datagrams destined for a host on one
    vlan can be visible on another vlan (which is obviously
    undesirable).
    Multiple stacks is a possibility here as well, but in embedded
    designs hardly an option....
    
    Erik

Simon

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