PIM-DM

PIM- Dense Mode:

• used in a situation:
• networks where many multicast clients are tightly spaced together in small networks.

PIM: Protocol Independent Multicast

• PIM is used for router to router communication.
• PIM depend upon the unicast routing protocols for topology information.
• Multicast groups can be either sparse or dense.
• Multicast interfaces are configured as either sparse or dense or both.
• PIMv2 hello message: 30sec
• on PIM enabled interfaces.
• PIMv2 hold time value: 90sec
• PIMv2 uses protocol 103 & reserved multicast address 224.0.0.13
• PIM mode only determine how traffic is send from an interface, not how it recieved.
• DR Router: single router send  IGMP host-query messages to host group membership
• Highest ip number will be DR
• Assert Forwarder: 
• one router will be elected & responsible for forwarding multicast traffic.
• AS election:
• admin distance to the source
• lowest metric to the source
• if tie, highest ip address

IGMP: Internet Group Management Protocol

• IGMP is automatically enabled when PIM enabled.
• IGMP enables the communication between multicast routers and their hosts.
• Multicast routers uses the IGMP to send ip packets to what multicast groups on what interfaces.
• Host Membership query:
• Routers use the queries to discover the presence of multicast group member on a subnet.
• general membership query is sent to the group address 0.0.0.0.
• group specific query is sent to the group address that is required.
• Host Membership Reports:
• Hosts replies to queries.
• 
  

RESERVED MULTICAST ADDRESSES

• 224.0.0.1 - All multicast hosts
• 224.0.0.2 - All multicast routers
• 224.0.0.4 - DVMRP routers
• 224.0.0.5 - OSPF routers
• 224.0.0.6 - OSPF DR routers
• 224.0.0.9 - RIPv2 routers
• 224.0.0.10 - EIGRP routers
• 224.0.0.13 - PIM routers
• 224.0.0.22 - IGMPv3
• 224.0.0.25 - RGMP
• 224.0.0.39 - Auto-RP announce (RP)
• 224.0.0.40 - Auto-RP Discovery (MA)

MULTICASTING

• multicast is udp based
• source address is always unicast address & never be multicast address.
• commands used are:
• sh ip mroute                                              // show the multicast routing table
• sh ip multicast interface                          //  shows multicast details for the interface
• clear ip mroute *                                 // clear routes from the multicast routing table
• ip multicast-routing                           // globally enables multicast routing on router
• ip multicast-routing distributed         // globally enables multicast routing on a 3560
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