The MPLS WG Archive

[IJsbrand Wijnands <ice@cisco.com>]

Hi,


>
> 2.3.1.1.  Determining one's 'upstream LSR'
>
>    A node Z that is part of P2MP LSP <X, Y> determines the LDP peer U
>    which lies on the best path from Z to the root node X. If there are
>    more than one such LDP peers, only one of them is picked.  U is Z's
>    "Upstream LSR" for <X, Y>.
>
> Which is the "best path" for Z. Two ways can determine the best path.
> 1. Z can look up the normal "route table", and get the best path  
> according the route.(The route table may be generated by OSPF, ISIS,  
> RIP, or even OSPF-TE)
>
> 2. Z can get the best path according the multicast table (this table  
> may be generated by various multicast routing protocols), and the P2MP  
> LSP or MP2MP LSP will only work on the routers that support  
> corresponding multicast routing protocols.

Can you give an example of a multicast routing protocol that populates  
such a table?

>
> The two ways are not compatiable, and the two P2MP LSPs or MP2MP LSPs  
> are defferent. Maybe this draft should describe the two ways, and  
> specify one way or both the two ways. The best path selection problem  
> should be solved.

Are you suggesting we should set priority to one table over the other?

It looks to me that the table selection is a local policy and does not  
necessarily need to be the same on each LSR. You may want to use a  
MuRIB between 2 LSRs just to make Multicast divert from Unicast for a  
specific link. How these two tables are used is up to the operator to  
define. It does not seems to be something the draft must spell out. So  
I think this is out side the scope of the document.

Thx,

Ice.

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