PIM OVERVIEW

PIM OVERVIEW
CONTROL PLANE-PIM
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Protocol independent Multicast
  - used for router to signal each other how to build mulitcast tree
Protocol independednt as it does not advertise it on topology information
   - implies IGP already runs in the network to build loop free topology
IOS runs pimv2 by default
    - ip pim version [1|2]
PIM modes control how the tree is built and who recieves what traffic
Dense Mode
 - considered implicit join
 -All traffic unless you say you dont want it
 - uses flood and prune behaviour
Sparse Mode
   - considered explicit join
   - no traffic unless you ask for it
   - uses a RP (Rendezvous Point) to process join requests
Sparse Dense Mode
   - sparse for groups with an RP assigned
   - Dense for all others
Control Plane MSDP
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Multicast source discovery protocol
    - used for RP to signal to each other about multicast senders (nothing to do with      
building multicast tree or locating reciver i.e not replacement for PIM works in      
conjuction with PIM
RPF Check prevents loop in the dataplane
    each and every packet is checked
      if incoming multicast interface = outgoing unicast interface (i.e route lookup) back to
      the source RPF is passed
       
       If it does not equal rpf is failed and packet is dropped
Dataplane-Multicast Routing TABLE
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Using PIM router learn where source and recievers exist
   - interface facing upstream towards source is the incoming interface
   - interface facing downstream towards reciever makeuo the "outgoing interface list" or the
      oil
   - split-horizon like behaviour stops an interface from being an oil if an incoming     
interface (can cause issue on nonbroadcast multipoint interfaces)
- If the rpf check passes
      we prefer (S,G) over (*,G) in routing table
      we switch packets from incoming interface to all interfaces in the OIL
So only one packet is recieved on incoming interface then replicated at layer 3 to all OIL
interfaces