Re: [pim] I-D ACTION:draft-ietf-pim-group-rp-mapping-01.txt

["Andy Kessler (kessler)" <kessler at cisco.com>]

Hi, 

I was speaking to Stig and we came up with what we think is a 
workable compromise for the hash function. 

After steps 1-8 of the algorithm have been executed we have
taken into account all of these factors: 

 Embedded RP
 SSM Range, Dense mode config
 Static with override
 Longest match
 Bidir over SM
 Mapping Origin - BSR, Auto-rp, static, other

The only type of Group-to-RP mappings that can be left at that point is 
a few overlapping mappings from only one of BSR, Auto-RP, static, or 
other. 

Step 9 currently says to pick the highest IP address. Taking into
account
the hash function for BSR and the issues with implementing the hash
with Bidir, we can add a new step 9 for the hash:

9. If the remaining Group-to-RP mappings were learned through  
   BSR and the PIM Mode of the Group is 'PIM-SM' then the hash 
   function will be used to choose the RP. The RP with the highest 
   resulting hash value will be selected. 

   * If more than one RP has the same highest hash value we 
     continue with the algorithm with those Group-to-RP mappings.

   * If the remaining Group-to-RP mappings were NOT learned from BSR 
     we continue the algorithm with the next step

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.


Then we can change section 9 which talks about "Migration to the new 
algorithm" to say that we will NOT remove the hash function and
therefore it will be backward compatible. 

Further, before the IETF meeting we will create an ascii flowchart of 
the algorithm and send it out to the list. 

Andy