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Re: [lwip-users] lwip minimal example, echo server

From: Matthias Dübon
Subject: Re: [lwip-users] lwip minimal example, echo server
Date: Tue, 7 Oct 2014 12:39:49 +0200

Hello Sergio,

thanks for your support, I found my mistake, I changed the IP address
from to because the is already
taken in my network. When using everything is working
fine. Hence I think I have to read something more about tap devices
and default gateways.


On Fri, Oct 3, 2014 at 3:27 PM, Sergio R. Caprile <address@hidden> wrote:
> OK, here I go...
> The UN*X examples use a tun/tap device, and there is a specific
> configuration parameter for different flavors of it. Check the Makefile
> for this, did you ?
> #To compile for linux: make ARCH=linux
> #To compile for cygwin: make ARCH=cygwin
> #To compile for openbsd: make ARCH=openbsd
> ARCH=linux
> Once you have the correct tun or tap device, it will show up in your
> ifconfig and you will be able to ping the lwIP stack as a new machine on
> a new network, which is what you should do first when debugging
> networking problems.
> In main.c:
>   /* startup defaults (may be overridden by one or more opts) */
>   IP4_ADDR(&gw, 192,168,0,1);
>   IP4_ADDR(&ipaddr, 192,168,0,2);
>   IP4_ADDR(&netmask, 255,255,255,0);
> So, will be the address of the gateway in your machine to
> "the lwIP network", via a tun or tap interface. In Linux seems to be tap
> tap0      Link encap:Ethernet  HWaddr 86:99:D8:CE:27:DC
>           inet addr:  Bcast:  Mask:
>           inet6 addr: fe80::8499:d8ff:fece:27dc/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:500
>           RX bytes:0 (0.0 b)  TX bytes:468 (468.0 b)
> The specifics to get the tap working are beyond my knowledge, I remember
> I just followed a tutorial. The interface will be up once the example is
> running, and will dissappear after that.
> Anyway, you should be able to ping that interface to check if the tap is
> working.
> And,  will be your "lwIP machine" address, you should be
> able to ping it
> address@hidden minimal]# ping
> PING ( 56(84) bytes of data.
> 64 bytes from icmp_seq=1 ttl=255 time=8.76 ms
> 64 bytes from icmp_seq=2 ttl=255 time=9.66 ms
> --- ping statistics ---
> 2 packets transmitted, 2 received, 0% packet loss, time 999ms
> rtt min/avg/max/mdev = 8.766/9.214/9.663/0.458 ms
> and you should be able to telnet to it in port 7, cause no one knows if
> your
> SimpleEchoClient really works, although you probably will.
> address@hidden minimal]# telnet 7
> Trying
> Connected to
> Escape character is '^]'.
> hola
> hola
> You probably noticed I run this as root... there are some permissions
> associated to the tap interface, and I'm lazy enough to change them.
> Anyway, you should see something like this:
> tapif: tapif_init: open: Permission denied
> if that is the case.
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