[Xorp-hackers] about the implementation of PIM-SM

[Li Chuanhuang]

Hi:

I'm reading the XORP source code,and I have two questions about the implementation of PIM-SM:

1:In the PIM-SM specification,Data Packet Forwarding Rules:
On receipt of data from S to G ,we should deceide whether the KAT should be set,at the same time, we should update the SPTbit(S,G,iif).But in the implementation(XORP),we'll do it only when we received the IGMPMSG_NOCACHE and IGMPMSG_WRONGVIF messages from the Kernel.This is the special cases,not every time we received the multicast data.

It seems that the implementation is unconformity with the specification,How to interpret it?

2:Because Linux Kernel only support (S,G) multicast forwarding entries,so XORP also only add the (S,G) entries to the Kernel MFC.
If the Kernel received a multicast packet and can't find a MRT in the MFC,it send the IGMPMSG_NOCACHE message to the PIM-SM module.Now we use the user-level task(PIM-SM module) to forward that packet?? is that right??

Hope your answers!!

Thanks and best regards!!
					Li Chuanhuang
					Zhe Jiang Gongshang University
					08/04/2006