Significance of Hash Mask length for RP selection

Frnds,

Can you tell me the Significance of Hash Mask length for RP selection in case of BSR appointment.

R2(config)#ip pim bsr-candidate loo 0 ?
  <0-32>  Hash Mask length for RP selection

Also, can you confirm:

 BSR- higher priority is preferred
 RP- lower priority is preffered

Thanks,

Comments

  • Yes, for BSR higher priority is preferred and for candidate RP lower priority is preferred. The hash mask length is not used by default. We can use the hash mask length to load balance between different RPs. Read this excellent blog article by Petr to have it explained more in detail:

    http://blog.ine.com/2009/04/07/understanding-bsr-protocol/

  • ashse,

     

    The hash is used for load-balancing purposes. Here is a link with a great explanation on this:

    http://blog.ine.com/2009/04/07/understanding-bsr-protocol/

    And you are right, BSR the higher the better, whereas RP the lower the better.

    Happy studies..

  • qqabdal

    quoted"And you are right, BSR the higher the better, whereas RP the lower the better." unquoted.

    This is a good one, I learned it in a hard way.  It would be nice if the winner for "both" BSR and RP is either higher or lower, it will certainly makes our life easier.

     

  • There's a little twist to the Candidate RP election. Don't forget these important points, because they often create unexpected behavior when you test in a lab:

    Cisco routers perform the following steps to determine which C-RP is used for a group:


    1. imageA longest match lookup is performed on the group prefix that is announced by the BSR C-RPs.

    2. imageIf more than one BSR-learned C-RP are found by the longest match lookup, the C-RP with the lowest priority (configured with the ip pim rp-candidate command) is preferred.

    3. imageIf more than one BSR-learned C-RP have the same priority, the BSR hash function is used to select the RP for a group.

    4. imageIf more than one BSR-learned C-RP return the same hash value derived from the BSR hash function., the BSR C-RP with the highest IP address is preferred.

     

    Number 4 always gets me. If everything is left as default, the Multicast routers would actually prefer the RP with the Highest IP address. This was taken from the Master Command Index:

    http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_04.html#wp1053348

  • qqabdal

    quoted"And you are right, BSR the higher the better, whereas RP the lower the better." unquoted.

    This is a good one, I learned it in a hard way.  It would be nice if the winner for "both" BSR and RP is either higher or lower, it will certainly makes our life easier.

     

    Fully agree with you, they got make it the harder way, otherwise, where is the entertainment?

Sign In or Register to comment.