[Xorp-users] Linux 2.6 multicast issue using PIM

[Arnaud Le Taillanter]

Bruce M Simpson wrote:
> On Mon, Aug 23, 2004 at 02:04:14PM +0200, Arnaud Le Taillanter wrote:
> 
>>Just out of curiosity, why is PIM kernel support necessary for the Xorp 
>>PIM daemon to operate?
>>I've successfully run XORP PIM on a FreeBSD box, I followed the 
>>documentation and enabled the kernel options MROUTING (fair :) and also
>>PIM, but I don't see why Xorp PIM would need PIM support from the 
>>kernel. Xorp BGP doesn't need BGP support from the kernel for example.
> 
> 
> BGP lives entirely in userland; it only requires specific kernel support
> in special circumstances (TCP-MD5).
> 
> PIM does not live entirely in userland. Multicast forwarding functions are
> located within the kernel.


Aren't the multicast forwarding functions being dealt with by the 
MROUTING (for FreeBSD) or CONFIG_IP_MROUTE (for Linux) kernel options?

In my thinking, the PIM XORP daemon then would only need to push out to 
the kernel the multicast routes it derived from its protocol activity, 
like BGP does with the unicast routes (via the forwarding engine 
abstraction). Perhaps PIM needs some information from the kernel about
multicast traffic coming through an interface (which may change the PIM
state)?

Arnaud


> 
> BMS
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