Re: [mpls] draft-wijnands-mpls-mldp-in-band-signaling - PIM-Bidir

[IJsbrand Wijnands <ice at cisco.com>]

Yakov,

> In the case where we have PIM-Bidir sender-only branches (that do not
> originate any PIM Join messages) what are "the IP multicast control
> messages used to set up the tree", and how do these messages get
> "translated into mLDP messages" ?

In PIM this will result in two different trees, one tree that  
represents the (*,G) for the receivers, the other being the (*,G/M)  
for the senders. The same will be true for mLDP. There will be two  
MP2MP LSPs, one encoding (*,G), the other (*,G/M). The only thing that  
we are doing is translate the PIM state into a mLDP LSP. This is what  
is described in section 2.2.

> > From section 2.2 of that draft:
>
> 2.2.  Transiting IP multicast bidirectional trees
>
>   Bidirectional IP multicast trees [RFC5015] MUST be transported  
> across
>   a MPLS network using MP2MP LSPs.  A bidirectional tree does not have
>   a specific source address; only the group address and subnet mask  
> are
>   relevant for multicast forwarding.  The RP for the group already
>   known by IP multicast is used to select the ingress PE and root of
>   the LSP.  The group address is encoded in either Section 3.3 or
>   Section 3.4, depending on the IP version.  The subnet mask  
> associated
>   with the bidirectional group is encoded in the Transit TLV.  There
>   are two types of bidirection states in IP multicast, the group
>   specific state and the RPA state.  The first type is typlically
>   created due to receiving a PIM join and has a subnet mask of 32 for
>   IPv4 and 128 for IPv6, the latter is typically created via the RP
>   mapping protocol and has a variable subnet mask.  The RPA state is
>   used to build a tree to the RP and used for sender only branches.
>   Please see [RFC5015] for more details.
>
> The above talks about "the group specific state" and "the RPA state",
>
> Could some of the branches of an MP2MP LSP be associated with just
> the RPA state, while other branches of the *same* MP2MP LSP be
> associated with the group specific state ? In other words, could

Yes.

> some branches of an MP2MP LSP be signaled using Transit IPv4 Bidir
> TLV with mask length less than 32 (the branches associated with the
> RPA state), while some other branches of *the same* MP2MP LSP be
> signaled using Transit IPv4 Bidir TLV with mask length 32 (the
> branches associated with the group specific state) ?

Yes.

> If yes, then what are the procedures at the nodes where the branches
> of the MP2MP LSP that are associated with just the RPA state merge
> into the part of the *same* MP2MP LSP that is associated with just
> the group specific state ?

This is documented in RFC5015 section 3.1.4. Its not mLDP's  
functionality to merge the 2 trees together, this is done in PIM.

Let me know if this addresses your concerns.

I will also update the bidir section to state the RP discovery is via  
static configuration.

Thanks for the comments,

Ice.