Re: [lwip-users] The lwip linux port - how to use another ip on the existing subnet

[Enrique Wellborn]

Thank you very much Sylvain.

Your nice solution answers my first question. In fact, I stumbled upon brctl once or twice in the past and I remember that working with it sometimes led to unpredictable results (like losing communication with my machine).

Yet, I'm still unsure about my second question - is there a worthy linux alternative to winpcap that works well with lwip and doesn't require adding a new device?

Thanks a lot guys,

Enrique.

On Sun, Oct 20, 2013 at 9:31 PM, Sylvain Rochet <address@hidden> wrote:

Hi Enrique,

On Sun, Oct 20, 2013 at 11:33:11AM +0200, Enrique Wellborn wrote:
> Hi,
> I was wondering whether it is possible to use the lwip linux port so that
> it'll use an ip address on my existing subnet.
> The scenario i'm trying to create is as follows:
> My Ubuntu machine has a single ethernet device (eth0) with ip:
> 192.168.0.3/24, gw: 192.168.0.1.
> I want to create an lwip application that will have ip addr 192.168.0.4 and
> the same mask and gw.
> I managed to do it using the windows port (that utilizes winpcap for the
> task) and it worked great, but when I'm running the simhost app(from the
> linux port) with the relevant arguments it just fails (I think it has
> something to do with it trying to create a tun device with an ip address
> that belongs to the existing subnet of eth0).
> So, I have 2 questions:
> 1. Is it possible to create a tun device with ip addr in the existing
> subnet of eth0?
> 2. Is there a linux alternative for winpcap that works well on linux (I saw
> that pcap was not supported on linux), in a way that will enable the above
> scenario?

What you are looking for is a Linux bridge:

brctl addbr br0
ifconfig br0 192.168.0.3 netmask 255.255.255.0
ifconfig eth0 0.0.0.0
route del default # probably not nessary
route add default gw 192.168.0.1
ifconfig br0 up
brctl addif br0 eth0
brctl addif br0 tap0 # once lwIP is running
ifconfig tap0 up

brctl show # should display the following:
bridge name     bridge id               STP enabled     interfaces
br0             xxx                     no              eth0
                                                        tap0
Sylvain

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