Re: [lwip-users] Multicast Example?

[Jonathan Ross]

The packets from my workstation do not have the trailing zeros, if that's what 
you mean. And wireshark doesn't say anything about those zeros, it just says 
they're there.

What I think I really need is someone telling me I'm doing everything right or 
I'm doing something wrong so I know where to focus my efforts at the moment. I 
think I see some multicast messages going to my device in wireshark, but I 
thought that I would get the message by listening via UDP on the interface for 
IP_ADDR_ANY and the port that the multicast packet is being sent to, but my 
udp_recv function is never called.

Supposing I did successfully subscribe to a multicast group, where would the 
data being multicast be found?

Thanks,
Jonathan


On Dec 17, 2009, at 1:43 AM, Simon Goldschmidt wrote:

> 
> Jonathan Ross wrote:
>> [..]
>> Did I do something wrong?
> 
> Unfortunately, I can't help you much there, as I don't really use IGMP... 
> However, your code does seem correct. Do other packets have trailing zeros? 
> What does wireshark say to those zeros?
> 
>> [..]
>> Also, xemac_add calls netif_add, and within which there is the following
>> code:
>> 
>>  netif->flags = 0;
>> 
>> // ...
>> 
>> #if LWIP_IGMP
>>  /* start IGMP processing */
>>  if (netif->flags & NETIF_FLAG_IGMP) {
>>    igmp_start( netif);
>>  }
>> #endif /* LWIP_IGMP */
>> 
>> How does igmp_start ever get called? I don't see any code in the file
>> (where I write //... above) that could reset the flag to include
>> NETIF_FLAG_IGMP.
> 
> The init function of your netif (passed to netif_add) should set the flags 
> (ARP if supported, IGMP if supported, etc). It gets called between the lines 
> you pasted above (at the place of "// ...").
> 
> Simon
> --
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