AI, ML, Development + Cisco Learning Blog Learning about Machine Learning, Artificial Intelligence, related devlopment topics and formerly Routing and Switching, Datacenter, Security and other topics, CCIE #23664, Frank Wagner

11. September 2006

important terms to know about Multicast

Filed under: Multicast — ocsic @ 13:43
  • IGMP – is used to track the multicast group members between hosts and routers on a lan
  • CGMP – Cisco Group Management Protokoll, for routers connected to catalyst switches
  • PIM – Protocol independet Multicast is for routers to know which multicast packets to forward and which not
  • DVMRP – Multicast used on the internet MBONE
  • Sparse Mode – unless there is an explicit request for traffic a router assumes that others routers do not want to forward traffic.When a host joins a multicast group, the connected routers send a PIM join message to the RP (rendezvous point). The RP keeps track of group mappings
  • Dense Mode – the router assumes that all other routers want to forward the multicast stream for a group, if a router receives a multicast and has no pim neighbor and no receiving host, it sends back a prune message to the source


Important commands:

ip pim send-rp-announce Configures a router to be the RP

ip pim send-rp-discovery Assigns the RP mapping agent

ip igmp join-group the router will accept multicast packets and also forward them

ip igmp static-group the router will not accept and only forward a multicast stream

RP (rendezvouz point)

  • A RP is acting as the central sender and receiver for data. Sources must send their data to the RP over a shared distribution tree. The RP is then just the initiator for new sessions between receivers and senders.
  • static versus Auto-RP
    • for Auto-RP a router must be designated as the RP mapping agent. This agent sends the group-to-RP mappings.

Good programm for generating multicast traffic is iperf. See the link provided below.


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