Subject: a quick questions about NCF in PGM

From: Xinming He <[email-masked]>
Date: Thu, 7 Jun 2001 21:33:08 -0400 (EDT)

When a network element(PGM capable) receives a NCF from its upstream
parent, will it forward the NCF to its downstream nodes, or discard the
NCF after establishing the neccessary state in itself? In the PGM
sepcification, it just says the NCF will be multicasted the group. Should
the network element really forward it to its downstream nodes when
receiving one from its parent? If yes, there seems to be too much control
traffic as a result of packet loss?

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From: Nidhi Bhaskar <[email-masked]>
Date: Thu, 7 Jun 2001 18:53:58 -0700 (PDT)

> NCF after establishing the neccessary state in itself? In the PGM

NCFs travel only 1 PGM hop.

> traffic as a result of packet loss?

They are multicast to the group address so that they can traverse any
non-PGM capable routers in the tree to reach downstream PGM nodes.

They carry the router alert option which causes each router to examine
them hop-by-hop and a PGM capable router to stop them from being
forwarded further than a single PGM hop.

Thanks,
Nidhi.