Re: [Gen-art] Gen-ART LC review of draft-ietf-pim-group-rp-mapping-07.txt

["Andy Kessler (kessler)" <[e-mail]>]

Hi, 

Thank you for the review. 
My comments are below annotated with Andy>

Andy


I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at
<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-pim-group-rp-mapping-07.txt
Reviewer: Brian Carpenter
Review Date: 2010-12-18
IETF LC End Date: 2010-12-23
IESG Telechat date: 

Summary: In good shape, a few issues.
--------

Major issues:
-------------

3.  Existing algorithm
...
   The algorithm defined in this document updates algorithm defined in
   PIM-SM ( Section 4.7.1 in [RFC4601]).  The new algorithm is backward
   compatible and will produce the same result only if the Group-to-RP
   mappings are learned from a single mapping source.

A logical implication of the last sentence is that if some of the Group-to-RP
mappings are learned from more than one mapping source, the new algorithm might 
not produce the same result as the existing algorithm. Is that indeed the case,
and if so, don't we have a problem until all PIM-SM routers have been updated?

Andy> Most vendors today do not officially support deployments with multiple
Andy> dynamic routing protocols. They probably have inconsistent results now. 
Andy> This algorithm will standardize the results for those vendors. It will
Andy> be more consistent when all vendors do support the new algorithm. 



5.  Common use cases

   o  Default static Group-to-RP mappings with dynamically learned
      entries

   Many network operators will have a dedicated infrastructure for the
   standard multicast group range (224/4) and so might be using
   statically configured Group-to-RP mappings for this range.  

Please indicate whether this issue also applies to IPv6.

Andy> There is no issue with IPv6. IPv4 has some older baggage because
Andy> the 224/4 addressing scheme has been around since before there was
Andy> SSM and BSR. IPv6 Multicast does not have that history. 



6.  Proposed algorithm
...
   10.  From the remaining set of Group-to-RP Mappings we will select
        the RP with the highest IP address.  This will serve as a final
        tiebreaker.

Please define "highest". Does it mean "greatest when considered as an
unsigned integer"?

Andy> This should be the same method that is used to pick 
Andy> the highest IP address in many protocols. One I know well is
Andy> the way that a designated router is selected in RFC 4601 in
Andy> section 4.3.2. The main part of the function says: 
Andy>      a.primary_ip_address > b.primary_ip_address
Andy> To me that has always meant you compare the first byte,  
Andy> then the 2nd, the 3rd and then the 4th. 
Andy> I don't know where that would be defined. Maybe someone else knows. 
Andy> It is not defined in RFC 4601. 


8.  Clarification for MIB Objects

   When a Group-to-RP mapping entry is created in the
   pimGroupMappingTable in the PIM-STD MIB[RFC5060], it would be
   acceptable to have an entry with an RP with address type 'unknown'
   and a PimMode of Dense Mode or SSM.  These entries would represent
   group ranges for Dense mode or SSM.

   Also all the entries which are already included in the SSM Range
   table in the IP Mcast MIB would be copied over to
   pimGroupMappingTable.  They would have a type of configSSM and an RP
   with address type 'unknown' as described above.

Is this section intended to be a normative update of RFC 5060, or is
it just commentary? The phrase "it would be acceptable" almost sounds
like a normative MAY.  

Also, shouldn't it be 'unknown(0)' in the context of the MIB? (This
applies in three places in the draft.)

Andy> At some point we received comments and requests to include all
Andy> the group mappings in this table - even for Dense Mode or SSM
Andy> which do not have an RP. We are merely stating that it OK to 
Andy> do that and use the RP address and type (of the RP) of unknown. 


Nits:
-----

5.  Common use cases
...
   o  More use cases

   By no means, the above list is complete.  Please drop a mail to
   'authors' if you see any other use case for this.

This seems a bit strange to appear in the final RFC; at the least it needs rewriting.

Andy> I agree. That was for the draft and should be removed. Should we
Andy> just remove the whole section ? Or change the wording to somehow
Andy> say there are more use cases that will benefit from this algorithm ? 



The checker says:

== There are 1 instance of lines with multicast IPv4 addresses in the
     document.  If these are generic example addresses, they should be changed
     to use the 233.252.0.x range defined in RFC 5771

Andy> We have discussed this before. We need to use the addresses that in the
Andy> examples. 239/8 is the Administratively Scoped Block as defined in RFC 5771.
Andy> Its the same thing for 239.100.0.0/16 in section 5. We were told to add
Andy> the comment that says its an administratively scoped multicast address
Andy> range. Using GLOP will not make the same point we are trying to explain.