CCIE RS – L3 Multicast – Implement and Troubleshoot IPv4 PIM

Implement and Troubleshoot IPv4 Protocol Independent Multicast (PIM)

PIM Dense Mode, Sparse Mode, Sparse-dense Mode

PIM must be enabled on every interface you want multicast traffic to be sent accross. This is configured manually

Enable globally: ip multicast-routing

PIM Dense Mode

  • Push model to flood multicast traffic
  • Initially floods multicast throughout entire network
    • Repeated every 3 minutes
  • Routers that have no downstream neighbors prune unwanted traffic
  • Source tree only (S,G)
  • Cannot be used to build a shared distribution tree
  • Interface > ip pim dense-mode

PIM Spare Mode

  • Pull model to deliver multicast traffic
  • Only segments with active receivers that explicity request data will receive traffic
  • Forwards data on a shared tree
  • Requires a Rendezvous Point (RP)
    • Must be administratively configured in network
  • Sources register with the RP
  • Edge sends PIM (S,G) join message to source
  • Unidirectional Shared Tree and Source tree
    • Router closest to source registers with RP
      • Creates a (S,G) between source and RP
      • Data is forwarded down the shared tree (*,G) towards the receiver from the RP
  • Interface > ip pim sparse-mode

PIM Spare-Dense Mode

  • Interface > ip pim sparse-dense-mode


Static RP, Auto RP, BSR


  • Ip pim rp-address [ip address] [acl]
  • Used by first hop router to send PIM register message on behalf of a host sending to a group


  • Cisco proprietary
  • Automates distribution of group to RP mappings in PIM network
  • Multiple RP’s can be used to serve different groups or be a backup of each other
  • First step
    • Designate an RP mapping agent
    • Receives the RP announcement messages
  • Sparse Mode environments need a default RP
  • Sparse Dense Mode do not
  • Announcing the RP
    • Ip pim send-rp-announce [type] [number] scope [ttl-value] [group-list acl] [interval in seconds]
    • ip pim send-rp-announce ethernet0 scope 16 group-list 1 access-list 1 permit
  • Assigning the RP mapping Agent
    • Router that sends authoritative discovery packets telling other routers group to RP mapping
    • Ip pim send-rp-discovery scope [ttl-value]
  • Show ip pim rp mapping
  • Multicast Addresses
  • Auto-RP Filters
    • Ip pim rp-announce-filter
    • Done on mapping agent
    • Prevents unwanted candidate RP announcement messages
  • Needs ip pim spare-dense-mode

BSR – Boot Strap Router

  • Can operate in ip pim sparse-mode
  • BSR Candidate RP
    • Ip pim bsr-candidate [type] [number] [hash-mask-length] [priority]
  • RP Candidate
    • Ip pim rp-candidate


BiDirectional PIM

Designed for efficient many to many communication

Traffic is only routed along a bidirectional shared tree that is rooted at the RP for the group

Forwarding traffic is based on (*,G)


Used for many to many applications

Must be enabled on all multicast routers in the domain

Not supported on NBMA networks

Traffic will always be forwarded to the RP of the multicast group


ip pim bidir-enable
ip pim rp-address [ip] bidir

Source Specific Multicast (SSM)

  • Requires IGMP version 3
  • Receive content directly from the source instead of using a shared RP
  • Removes requirement for an RP
  • Router closest to the receiver will “see” a request to join a particular multicast source
  • Router sends requests directly to the source
  • Uses Source Tree multicast routing
    • No shared tree, no RP required
  • Routes traffic based on full (S,G) address
  • RFC3569


global > ip pim ssm [default]
interface > ip pim sparse-mode
interface > ip igmp version 3

Click to access imc-ss-mc.pdf

Group to RP Mapping

Ability to have a different RP announced for different multicast groups


Multicast Boundary

Administrative scoped boundary on an interface for multicast group address

  • Standard ACL
  • Blocks for group in both directions
  • Allows same multicast group to be reused in different administrative domains

Interface > ip multicast boundary access-list [filter-autorp]

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