[ECOS] Re: How to add multicast route? - how to add/remove a route

[Lambrecht Jürgen]

Hello Grant,

I guess my answer is a bit late, but also for posterity's sake ;-), and 
your code worked for me, thanks.

So with the code found here: 
http://sourceware.org/ml/ecos-discuss/2011-03/msg00185.html, you can add 
an entry in the routing table.
I updated the code, see attach.
Maybe this code could be added to 
ecos/packages/net/bsd_tcpip/current/src/ecos/support.c?

However, to add/delete a multicast entry, we do it in another way, from 
code we ported from Linux to eCos:

int LeaveMulticast(unsigned long multicastAddr)  /* Adress of the multicast group */
{
    struct ip_mreq ipMreq;     /* Argument structure to setsockopt */

    ipMreq.imr_multiaddr.s_addr = htonl(multicastAddr);

    /* Unicast interface addr from which to receive the multicast packets */
    ipMreq.imr_interface.s_addr = htonl (INADDR_ANY);

    /* Set the socket option to leave the multicas group */
    if (setsockopt (globalSocket, IPPROTO_IP, IP_DROP_MEMBERSHIP,
       (char *)&ipMreq,  sizeof (ipMreq)))
    {
    ...}
}

int JoinMulticast(unsigned long multicastAddr)  /* Adress of the multicast group */
{
....idem
    /* Set the socket option to join the MULTICAST group */
    if (setsockopt (gMDSocket, IPPROTO_IP, IP_ADD_MEMBERSHIP,
       (char *)&ipMreq,  sizeof (ipMreq)) == SOCKET_ERROR)

Those socket defines are in 
ecos/packages/net/bsd_tcpip/current/include/netinet/in.h:

And this is the resulting routing table:

Destination     Gateway         Mask            Flags    Interface
0.0.0.0         10.0.0.1        0.0.0.0         UG       eth0
10.0.0.0        10.0.0.0        255.255.240.0   U        eth0
127.0.0.0       127.0.0.1       0.0.0.0         UG       lo0
127.0.0.1       127.0.0.1       0.0.0.0         UH       lo0
224.0.0.0       224.0.0.0       0.0.0.0         U        eth0

(mark, I don't know why the Mask is always 0, this is not correct, 
because to delete an entry, you must specify the correct mask! That is 
why I added the correct mask myself for eth0 in my notes.)

On 04/01/2011 04:59 PM, Grant Edwards wrote:
> On 2011-04-01, Grant Edwards<grant.b.edwards@gmail.com>  wrote:
>
>> I think next I'll try passing either my own address (10.0.0.102, or
>> the local network 10.0.0.0 and see what happens).
> Specifying 10.0.0.0 as the gateway address works.  Oddly, the
> resulting routing table looks like this:
>
>    Destination     Gateway         Mask            Flags    Interface
>    10.0.0.0        10.0.0.0        255.0.0.0       U        eth0
>    224.0.0.0       224.0.0.0       240.0.0.0       U        eth0
>
> Specifying 10.0.0.0 as the gateway results in the route I wanted with
> 224.0.0.0 as the gateway.  Specifying 224.0.0.0 as the gateway fails.
>
> IMO, that's a bug, but whatever...
>
> So for posterity's sake, the initial routing table looked like this:
>
> Destination     Gateway         Mask            Flags    Interface
> 10.0.0.0        10.0.0.0        255.0.0.0       U        eth0
>
> And the contents of rtentry to add the multicast route were:
>
>        rt_dst = 224.0.0.0
>    rt_genmask = 240.0.0.0
>    rt_gateway =  10.0.0.0
>      rt_flags =    RTF_UP
>
> It turns out that the rt_dev field is ignored (or at least redundant).
Indeed, that is also what I noticed.
> That's different than the way Linux works: if you specify a device,
> you don't specify a gateway.  I'm not sure what the rt_dev field is
> for with the FreeBSD stack...
>
Kind regards,
Jürgen

-- 
Jürgen Lambrecht
R&D Associate
Tel: +32 (0)51 303045    Fax: +32 (0)51 310670
http://www.televic-rail.com
Televic Rail NV - Leo Bekaertlaan 1 - 8870 Izegem - Belgium
Company number 0825.539.581 - RPR Kortrijk

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