[ECOS] Re: How to add multicast route?

[Grant Edwards <grant dot b dot edwards at gmail dot com>]

On 2011-03-31, Grant Edwards <grant.b.edwards@gmail.com> wrote:

> I'm trying to figure out how to add a route to tell the stack which
> interface to use for sending UDP multicast packets, and I'm stumped.
> I've searched the list, and this exact same question has been posted
> multiple times, but it's never been answered.
>
> #define AssembleIP(a,b,c,d) (((a)<<24)|((b)<<16)|((c)<<8)|(d))
>
>   struct sockaddr_in  addr;
>   struct ecos_rtentry route;
>
>   memset(&route, 0, sizeof route);
>   memset(&addr, 0, sizeof addr);
>
>   addr.sin_family = AF_INET;
>   addr.sin_len = sizeof addr;
>
>   addr.sin_addr.s_addr = htonl(AssembleIP(224,0,0,0));
>   memcpy(&route.rt_dst, &addr, sizeof route.rt_dst);
>   memcpy(&route.rt_gateway, &addr, sizeof route.rt_gateway);
>
>   addr.sin_addr.s_addr = htonl(AssembleIP(240,0,0,0));
>   memcpy(&route.rt_genmask, &addr, sizeof route.rt_genmask);
>
>   route.rt_dev = "eth0";
>   route.rt_flags = RTF_UP;
>   route.rt_metric = 0;
>   
>   if ((rc=ioctl(s, SIOCADDRT, &route))) 
>     diag_printf("Error setting multicast route (SIOCADDRT): %s\n", strerror(errno));
>
> The ioctl always fails with the error "Network is unreachable"

In case it helps, I've dumped the network tables both before and after
the failed attempt to add a route:

Routing tables
Destination     Gateway         Mask            Flags    Interface
10.0.0.0        10.0.0.0        255.0.0.0       U        eth0     
Interface statistics
eth0    IP: 10.0.0.102, Broadcast: 10.255.255.255, Netmask: 255.0.0.0
        UP BROADCAST RUNNING MULTICAST MTU: 1500, Metric: 0
        Rx - Packets: 0, Bytes: 0, Tx - Packets: 0, Bytes: 0
        
Error setting multicast route (SIOCADDRT): Network is unreachable

Routing tables
Destination     Gateway         Mask            Flags    Interface
10.0.0.0        10.0.0.0        255.0.0.0       U        eth0     
eth0    IP: 10.0.0.102, Broadcast: 10.255.255.255, Netmask: 255.0.0.0
        UP BROADCAST RUNNING MULTICAST MTU: 1500, Metric: 0
        Rx - Packets: 0, Bytes: 0, Tx - Packets: 0, Bytes: 0
        

, and
> subsequent packets sent to 224.x.x.x. fail with "No route to host".  
> I've also tried setting rt_gateway to 0's (which appears to be how
> it's done on Linux).
>
> I tried setting the RTF_MULTICAST flag, but that's not supported by
> the ecos_rtentry structure (the rt_flags field isn't big enough).
> I've also tried setting the RTF_GATEWAY flag and the RTF_STATIC flags,
> and neither made any difference.
>
> How do you add a network route for multicast?



-- 
Grant Edwards               grant.b.edwards        Yow! Now that I have my
                                  at               "APPLE", I comprehend COST
                              gmail.com            ACCOUNTING!!


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