[Xorp-users] Xorp-users Digest, Vol 10, Issue 20 : Change in RP vs change in next-hop for RP (Vikram KAUL)

[Neeraj Prasad]

Hi,

Things will be handled differently for (*,*,RP) and (*,G).
For (*.*RP) -
------------------
See Section 4.1.2 :  (*,*,RP) State

The information for RP is really not required for (*,*,RP) case. This is why
RFC 4601 does not specify requirement to store 'Last RP used' for (*,*,RP)
state. The initiator of (*,*,RP) has to re-initiate the new Join for the new
RP and if it wants then can send a Prune for Last RP. As long as the RP is
reachable it does not matter.

For (*,G)
-------------
See  Section 4.1.3:  (*,G) State

The state machine should store the 'Last RP used'. Since this information is
present with us we can send a Prune to the Old RP and send Join to the new
RP.

This is specially important in BSR systems where a Candidate RP may be
changing so each time you will have new RP set to deal with. So the RP set
will be refreshed and old RP will be pruned off and new RP will be joined.

See the following Extract -

Section 4.7.1.  Group-to-RP Mapping
   . . .
   Note that if the set of possible group-range-to-RP mappings changes,
   each router will need to check whether any existing groups are
   affected.  This may, for example, cause a DR or acting DR to re-join
   a group, or cause it to restart register encapsulation to the new RP.
   . . .

For (S,G) Register process the standard has definitions which you know.

Please let me if this was helpful.

Thanks and Regards,
Neeraj.







On 2/1/07, xorp-users-request at xorp.org <xorp-users-request at xorp.org> wrote:
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>    1. Change in RP vs change in next-hop for RP (Vikram KAUL)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 31 Jan 2007 11:33:10 -0500 (Eastern Standard Time)
> From: Vikram KAUL <vkaul at research.telcordia.com>
> Subject: [Xorp-users] Change in RP vs change in next-hop for RP
> To: xorp-users at xorp.org
> Message-ID: <Pine.WNT.4.60.0701311114130.2784 at vkaul-laptop>
> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
>
>
> Hi,
>
>   Just wanted to verify the current implementation in XORP regarding
> events that might occur when a group G is active and data is being
> forwarded for that group. The (*,G) and (*,*,RP) state will exist in the
> router.
>
>   When the next-hop to the RP changes, the Upstream (*,*,RP) Join/Prune
> state machine which keeps the last RPF Neighbor towards that same RP, is
> triggered into sending a new Join(*,*,RP) to the new upstream neighbor and
> a Prune(*,*,RP) to the old upstream neighbor.
>
> This I can see in  pim_mre_rpf.cc
> PimMre::recompute_nbr_mrib_next_hop_rp_rp_changed()
>
>   However, I was not able to find what happenes when the RP itself changes
> when the group is active. The specs talk aboutthe "RP changed" impacting
> only the  "Per-(S,G) register state machine at the DR". (Look at the
> tabular form, last column, Section 4.4.1). The register tunnels get
> updated via an "update register channel" procedure when the state is Join.
>
>   Specifically, where are the conditions addressed when the RP itself
> changes for the (*,G) and (*,*,RP) state. Not the next hop changes, but
> the RP changes when the group is active. Is the protocol designed to
> handle this ?
>
>   Any pointers to the XORP code and/or the specs will be appreciated
>
> regards..
> Vikram
>
>
>
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> End of Xorp-users Digest, Vol 10, Issue 20
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-- 
Thanks and Regards,
Neeraj Prasad
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