From: Tom Martin (tig@wiltecinc.com)
Date: Sun Jul 18 2004 - 12:26:58 GMT-3
I have a question regarding PIM Proxy Registration: http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcpt3/1cfmulti.htm#1028916
I understand that in order for a sparse-mode domain to be able to join traffic sourced from a dense-mode domain that the RP must know of the sources within the dense-mode domain, hence the "ip pim dense-mode proxy-register" command.
What I can't seem to grasp is the requirement that for a dense-mode receiver to receive multicast groups from the sparse-mode domain that there must be a sender for that group already in the dense-mode domain.
The logic Cisco provides seems flawed:
- A sender in the DM region triggers proxy registration in the border router
- The border router joins the multicast group and forwards sources in the sparse domain to the dense domain
- If there is no sender in the dense mode region for a multicast group then no traffic will be forwarded into the dense-mode region from the sparse-mode region.
It would seem to me that the border router should either send a join towards the RP (SM behavior), or not knowing of any sources first-hand do nothing (DM behavior). Why does proxy registration affect the way that the dense-mode domain receives sparse-mode traffic?
Thanks,
Tom
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