1. PIM MTID point on draft-ietf-pim-mtid-01 PIM Working Group IETF 75 meeting Stockholm (Sweden) July 2009

2. Conditions for transient loops Mcast routing loops occur: when one node has to send both a Join and a Prune for the same MDT in different directions if topological change implies that downstream node of a failed node will become an upstream node  if a path from the failed node toward the source/RP on new topology traverses a prior downstream node when distance from downstream node (i.e. node B) to its parent node traversed by the MDT in direction of source/RP (i.e. node A) in the old topology is higher than the same distance in the new topology: d(A,B) new < d(A,B) old Check Procedures List the nodes that will be traversed by the Join message in the new topology from the failed node Check cycles of size 1,..., n-1, n (leads to cycle detection scheme)

3. Example (2-Cycle) w/o MTID Cycle of size 2 if – node A sends Join message to node B – and node B treats the Join message and stored corr. entry in its MRIB/MFIB – and node B has not sent Prune message yet or if node A has not yet treated Prune message sent by node B Then, the two MDT (old and new one) coexist for a period PruneJoinPruneJoin New MDT Old MDT A A B B

4. Example (2-Cycle) w/ MTID Conditions become: – node A sends Join message (MTID=2) to node B – and node B treats that Join message (MTID=2) and stored corr. entry in its MRIB/MFIB – and node B has not sent Prune message (MTID=1) yet or if node A has not yet treated Prune message sent by node B Then, the two MDT (old and new one) coexist for a period but now with different MTID (RPF selector) but necessitates specific mcast packet "differentiation" -> Traffic diversity can not be enforced by MTID Join (MTID 2) Prune (MTID 1) New MDT Old MDT Join (MTID 2) Prune (MTID 1) A A B B

5. Other conditions Topological diversity can not be enforced by MTID Note: MTID can enforce known MDT topology (-> static) B B Join (MTID 2) Prune (MTID 1) Join (MTID 2) Prune (MTID 1)Join (MTID 2) A A C C

6. Next Steps In PIM MTID Document loop conditions First step: specify mitigation means (without additional protocol procedures) Other I-D Second step: specify mitigation/ avoidance means (possibly by additional protocol procedures)