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Multicast and Multicast Routing
Unicast vs Multicast
- Routed via PIM ( Protocol Independent Multicast ).
- Always UDP-Based ( Video, Audiostreams, some kinds of data ).
- Typical network challenges ( QoS, Security, Bandwidth consumption).
- Began as a ‘speciality’ technology, becoming heavily adopted in modern times.
- Multicast group members receive all data center to a group.
- Multicast IPv4 Range: [ 220.127.116.11 18.104.22.168 ]
- Filtering tip:
- Last 23 bits of IP mapped to MAC
- Can lead to overlapping addresses
- Routing based on source address.
- Multicast sources can just ‘start’ transmitting.
- Routing is called reverse path forwarding ( RPF ).
- Clients jump into a stream with a JOIN Message.
- (S,G) Pair
- Shortest Path Tree (SPT), eats resources, shortest path
- Shared Tree – Uses rendezvous point ( RP) less resources, sub-optimal paths
- Switches flood multicast by default
- Add IGMP Snooping
- Only modes use to be PIM SparseMode and PIM DenseMode
- Uses a rendezvous point ( usually a router )
- Rendezvous points uses a shared tree.
- Isn’t flooded but requested
- PIM-SM is now PIM Any-source Multicast. Uses a Shared Tree , Source tree combo
- Floods the network
- Prune messages from sources to cut the stream
- A lot of multicast sources can impact the network
Mirrored paths with Bidirectional PIM
- Used for things like Teleconferences
- Rendezvous Point ( RP ) is selected and everything is routing through it
- ( * , G ) is used for all traffic
- Only shared tree is used
Direct Contact with Source Specific
- Multicast receiver gets server address from outside source
- Outside source delivers (S,G) Pair
- Requires requesters to use IGMP V3 ( asks for S,G instead of just G )
Finding your Rendezvous Point
- IPv6 method works for IPv4 ( DNS / Multicast ).
- Assign the same address and let the routing table figure it out who is close.
- Static RP
- Auto RP
- Cisco Proprietary
- Holds election for C-RP ( Canidate Rendezvous Points)
- uses 22.214.171.124 for the election
- Highest IP address wins
- the router will announce it’s the canidate to 126.96.36.199
- Bootstrap Router
- Industry standard method implementing Auto RP
- Holds an election
- Canidate Boostrap Router
- Priority is configured on C-RP. The C-BSTR sends the list of C-RP
- The other router figure out which C-RP to use based on a hashing algorithm.