[Xorp-users] Problems with multicast routing on Linux

[Jon-Olov Vatn]

Hi Pavlin,

Thanks for the quick response! I am aware about the issues you list, and 
I should have been clearer about the situations when static multicast 
routing could be of interest. As you point out static multicast routing 
won't handle situations where the multicast group address(es), senders 
and group membership are neither static nor known in advance.

Regards,

J-O

Pavlin Radoslavov skrev:
> Jon-Olov Vatn <jon-olov at ontimenet.com> wrote:
>
>   
>> Pavlin Radoslavov skrev:
>>     
>>> If you want multicast forwarding between two segments, you MUST use
>>> a multicast routing protocol like PIM-SM.
>>> The purpose of IGMP is to inform the multicast routing protocol
>>> about directly connected receivers. Then it is up to the multicast
>>> routing protocol to modify the multicast forwarding entries in the
>>> kernel.
>>>   
>>>       
>> Is it really necessary to use a multicast routing protocol, or could the 
>> forwarding tables be configured statically, e.g., with "route add ..."? 
>>     
>
> In general you can't use commands like "route add" to install
> multicast forwarding entries in the kernel.
>
> Unlike unicast static routes, multicast static routes shouldn't be
> used primarily for the following two reasons:
>
> (a) multicast receiver membership is dynamic in nature and this
>     can't be tracked by (multicast) static routes.
> (b) If you create a multicast routing loop (which can easily happen
>     with static routes), then you can easily bring down your network
>     due to the exponential amplification of the looping
>     packets.
>
> I haven't used smcroute, but if you use it you need to understand
> the above two issues.
>
> Regards,
> Pavlin
>
>   
>> I understand that it useful to use a routing protocol, but for a small 
>> network with one or two routers it may be of interest to support 
>> multicast routing without deploying, e.g., PIM-SM or DVMRP. When 
>> googling I found smcroute (http://www.cschill.de/smcroute/) which seems 
>> adequate for such situations, but I have not tried it and since the last 
>> release is from 2002 I'm a bit suspicious ... Anyone out there with 
>> experience of smcroute or setting up static multicast forward entries in 
>> Linux in general?
>>
>> Mvh J-O
>>
>>
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>
>