Subject: [mpls] Re: Some questions about draft-ietf-mpls-ldp-p2mp-01, thank you!

From: IJsbrand Wijnands <[email-masked]>
Date: Mon, 10 Jul 2006 16:38:18 +0200

Jin,

>
>  Can you give an example of a multicast routing protocol that  
> populates  
>  such a table?
>
> jin.lizhong:Different multicast routing protocols may generate  
> different trees
> (the tree may be generated by DVMRP or PIM-DM protocol). Z can  
> determine the
> upstream LSR by following the multicast routing protocol messages. Then
> the P2MP or MP2MP LSP is identical to the L3 multicast tree. Which is
> the best path for Z is hard to say, the path determined by unicast  
> routing
> protocols or multicast routing protocols.

The only multicast routing protocol that creates its own unicast path  
is DVMRP. It is very unrealistic that customers will use DVMRP to  
create a unicast table that LDP will use to build the P2MP or MP2MP  
LSP.

>
>
> >
>  > 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.
>
> jin.lizhong:Firstly, we should describe the "best path" in more detail.

The best path is what unicast gives us if you do a lookup for the root  
address.

> The two selection methods are not compatiable and P2MP or MP2MP LSP  
> will
> not be setup sucessfully if different methods are used in Root Node,  
> Transit
> Node, and Leaf Node. What's more, if Root Node does not support  
> multicast
> routing protocols and Leaf Node only support multicast routing lookup
> method. Then the Leaf Node will not find the Root Node, for the Root  
> Node
> is out of the sight of Multicast domains.

I don't see what the problem is you are trying to solve. Why would you  
want to run a multicast routing protocol in the MPLS network to provide  
path to the root? Do you really consider DVMRP here? That is going  
backwards in time, just like proposing to use RIP.

Normal best path procedures apply to unicast routing tables, like admin  
distance and metric. If you have different unicast tables it is up to  
the administrator to set which table has preference.

Thx,

Ice.

> Secondly, we should specify the concept of "best path". Then we can  
> set a
> priority to one table over the other, or we can only select one  
> selection
> method.
>
>  Thx,
>
>  Ice.
>
>  >
>  >
>  >
>  >
>  >
>  >
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---

From: [email-masked]
Date: Tue, 11 Jul 2006 19:58:27 +0800

Hi, Ice
  pls. see the following lines began with jin.lizhong

==========================================================
From:IJsbrand Wijnands <[email-masked]>
To:[email-masked]

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?

jin.lizhong:Different multicast routing protocols may generate different 
trees
(the tree may be generated by DVMRP or PIM-DM protocol). Z can determine 
the
upstream LSR by following the multicast routing protocol messages. Then 
the P2MP or MP2MP LSP is identical to the L3 multicast tree. Which is 
the best path for Z is hard to say, the path determined by unicast routing
protocols or multicast routing protocols.

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

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.

jin.lizhong:Firstly, we should describe the "best path" in more detail.
The two selection methods are not compatiable and P2MP or MP2MP LSP will
not be setup sucessfully if different methods are used in Root Node, 
Transit
Node, and Leaf Node. What's more, if Root Node does not support multicast
routing protocols and Leaf Node only support multicast routing lookup 
method. Then the Leaf Node will not find the Root Node, for the Root Node
is out of the sight of Multicast domains. 
Secondly, we should specify the concept of "best path". Then we can set a
priority to one table over the other, or we can only select one selection
method.THX

Thx,

Ice.

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This message has been scanned for viruses and Spam by ZTE Anti-Spam system.
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