Subject: [pim] Questions re draft-ietf-pim-join-attributes-01

From: Stig Venaas <[email-masked]>
Date: Thu, 16 Mar 2006 13:35:35 +0100

Maybe it's a bit late for me to comment on this now, but anyway...

At the end of 3.5.  Attribute Convergence, it says:

    be sent.  This PIM Prune does not need to carry any attribute, the
    sender of the prune and the source and group information is enough to
    identify the entry.  The attribute information is removed immediately
    and possibly a new attribute is chosen from the database if
    available.

I don't understand this last sentence. Could you tell me what it means?

I've started wondering how things should behave when there are multiple 
non-conflicting attributes. Let me try to give an example.

Let's say we have this scenario (using part of diagram from draft):

                               ( Edge B1 )---- [R1]
                              /
                             /
    [S]              ( Core )
      \             /        \
       \           /          \
        ( Edge A2 )            ( Edge B2 )---- [R2]

Assume that Core receives (S,G)-joins from both B1 and B2 (same source 
and group) where B1 has specified one attribute a1 and B2 another 
non-conflicting attribute a2.

My question is what attributes core should include in the (S,G)-join 
sent to A2.

Let's assume that Core has no state, and then B1 sends the join first. 
Then Core would send join to A2 including the attribute a1. Then assume 
that B2 sends a join shortly after with attribute a2. Should Core then 
send a new join to A2 including both a1 and a2 or just a2? I would guess 
so, but not sure.

Let's say that B1 and B2 periodically send (S,G)-joins with these same 
respective attributes. Would Core then periodically send (S,G)-joins to 
A2 with both a1 and a2 included? Again, this is what I guess, but this 
is not so clear either.

In general where there are different types of attributes mixed, would 
there be any requirements on the order? I guess there might be since the 
draft says:

3.6.  Multiple attributes

    A PIM Join can contain multiple attributes.  The attributes are
    encoded as TLVs associated with a new PIM source type in the PIM
    message.  When a PIM Join with multiple attributes is received, the
    first attribute is processed, and the action taken depends upon the
    attribute type.  This may or may not result in the processing of the
    next attribute.  Attributes that the router understands but are not
    processed MUST be passed upstream unchanged.

I suppose requirements on ordering might be specified in the different 
attribute specifications.

Stig

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From: Arjen Boers <[email-masked]>
Date: Tue, 21 Mar 2006 09:36:53 -0600

Stig,

>    and possibly a new attribute is chosen from the database if

Given your topology below, suppose B2 sens a prune to Core, then Core
removes the entry with attributes from B2 and starts using the attributes
from B1, in the case it stored them.

> My question is what attributes core should include in the (S,G)-join 

Core only uses the attributes from the pim neighbor with the lowest ip address,
so the attributes are not merged.

> attribute specifications.

Yes.

Arjen.