1. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 1 PIM Dense Mode GateD Implementation Kurt Windisch Dave Meyer Advanced Network Technology Center University of Oregon

2. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 2 Outline n PIM-DM Overview n GateD Implementation n Issues n Status n http://www.antc.uoregon.edu/GATED/

3. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 3 PIM-DM Overview Key Features n Uses existing unicast routing protocols n Data-driven flood-and-prune strategy n Efficient when membership is dense n Builds optimal source-based trees n Soft state draft-ietf-idmr-pim-dm-06.txt, S. Deering, D. Estrin, D. Farinacci, V. Jacobson, D. Meyer, L. Wei

4. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 4 Broadcast and Prune n Broadcast and prune behavior ä Assume everyone wants the data ä A router broadcasts data until downstream router says “I don’t want this data” ä Send prune messages upstream to stop data flow – Prune state must be maintained, even if not “on-tree” ä Builds source based distribution trees

5. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 5 PIM-DM Overview n Reverse Path Forwarding (RPF) n Tree maintenance via Prune and Graft n State space: O (S x G) sender receiver R 2 R 3 R 1 R 4

6. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 6 Reverse Path Forwarding (RPF) n RPF check: In order to forward a multicast datagram, a router checks if the packet is received on the interface it would use to forward a unicast packet back to the source ä If the RPF check succeeds, the router forwards the packet ä If the RPF check fails, the packet silently discarded

7. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 7 RPF In PIMDM n RPF builds spanning tree ä Dalal & Metcalfe, ACM 21(12), 1978 ä Fully distributed n Reverse Path Multicast: ä RPF + Prune on RPF failure ä stops unnecessary traffic in addition to breaking loops. sender receiver prune data

8. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 8 Prune n Prune ä for a given (S,G) send Prune to upstream neighbor when outgoing interface list becomes empty ä upstream receiver prunes the receiving interface if no other routers or members are receiving (S,G). sender receiver R 2 R 3 R 1 R 4

9. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 9 Graft n Graft ä for given (S,G), send Graft to upstream neighbor when the outgoing interface list becomes nonempty ä upstream receiver adds receiving interface to outgoing interface list and begins forwarding (S,G) sender receiver R 2 R 3 R 1 R 4

10. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 10 Multiaccess LAN n Delayed prune and join ä When a downstream router on a LAN sends a Prune, other downstream routers must override with a Join if they are forwarding ä Therefore, handling of prunes is delayed while all routers listen for and send Joins to cancel the Prune. sender receiver R 2 R 3 R 1

11. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 11 Multiaccess LAN n Assert ä handles parallel paths from a source to a LAN ä election of single forwarder ä routers send Assert if they receive (S,G) data on an outgoing interface. ä Assert message contain metric to source ä all routers listen to determine winner sender receiver R 2 R 3 R 1 R 4

12. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 12 Dense Mode Tradeoffs n Advantages ä Source trees fully distributed ä Optimal reverse paths/low delay n Disadvantages ä O (S x G) state requirement ä May carry (S,G) for every S in the internet ä (S,G) prune state even though not “on- tree” ä Data driven forwarding state construction

13. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 13 Implementation Details n Compliant with PIM v2 specification n Based on GateD PIM-Sparse implementation by George Eddy (ISI) n Shared PIM code (SM/DM) n Requires PIM Kernel Patches ä yet to be standardized between PIM implementations

14. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 14 Implementation Details n Utilizes GateD v5 abstractions and protocols: ä Multicast Border Router (MBR) layer ä Multicast Routing Table (MRT) layer ä IGMP ä Unicast routing protocols n PIM-DM is a good fit for this architecture

15. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 15 MBR Interactions n Creating routing state ä sg_creation_recv: creates (S,G) entry with forwarding state (implements flooding) n Outgoing interface changes ä sg_join_recv: PIM-DM sends (S,G)-Graft upstream ä sg_prune_recv: PIM-DM sends (S,G)-Prune upstream

16. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 16 MBR Interactions n RPF check ä wrongif_recv: PIM-DM sends (S,G)-Assert or Prune on receiving interface n Group membership changes ä igmp_add ä igmp_delete

17. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 17 MRT Interactions n Multicast routing tables store PIM per (S,G) state ä incoming interface ä outgoing interfaces ä hooks to PIM-DM data structures for prune and assert state

18. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 18 Unicast Interactions n PIM relies on underlying GateD unicast protocols ä RPF checks ä flashing unicast route changes n Tested successfully with: ä RIP v2 ä OSPF v2

19. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 19 Issues n Scalability ä State space ä PIM-DM per (S,G) timers: O (S x G x n) timers that must be managed with fine granularity n Integration with PIM Sparse Mode n Need for tunneling (GRE)

20. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 20 Status Report n Basic implementation and testing done n To Do: ä known bugs ä larger scale testing ä performance/scalability studies ä interoperability testing ä Further implementation: GRE tunneling, IPv6, stand-alone PIM-DM ä Prune Refresh extensions

21. Kurt Windisch -- University of OregonIETF GATED -- December 7, 1997 21 Final Remarks n Call for test sites Further Info: http://www.antc.uoregon.edu/GATED/