ICMP issue while multiple interface in the same subnet

[Ronnel P. Maglasang]

what are the IP addresses of your nics in
Host1 and Host2? they should be in different networks (e.g. 10/8 and
172.16/16) for this to work.

myronn at seed.net.tw wrote:
> Hi,
>   For a special test reason, I must use two hosts and it has two interfaces to connect each other without any switch or hub.  
>  Host1                   Host2
> |-----|                 |-----|
> |   1 0-----------------0 1   |
> |     |                 |     |
> |   2 0-----------------0 2   |
> |-----|                 |-----|
>
>   Host platform OS is BSD.  I assigned Host1 NIC1 ping Host NIC2.  Command is correct but I found as follows:
> 1. Host1 arp broadcast to Host2 and Host2 would be return info to Host1. 
> 2. Then, Host1 sent ICMP request packet to Host2.
> 3. Host2 received packet and always "USE" NIC2 replaying the ICMP reply.
> 4. If Host1 use NIC2 ping Host2 NIC2, Host1 NIC2 could get the ICMP reply packet from Host2 NIC2.
>
> Question:
> 1. This behavior is a normal network behavior?
> 2. If it's a normal network behavior, it followed which standard?
> 3. I know that there were other softwares could change this behavior but why many platforms(BSD,Linux,.....) used this behavior was its default network behavior?
> 4. Why default behavior is incoming interface different from outgoing interface?
> 5. If I set all interfaces are in the same subnet and the incoming interface is the same with outgoing interface, what weakness would be happened?
>
> Thanks and Regards,
> Myron
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