Multicast is a mechanism where host transmitting a single copy of data to a multicast group, and multicast routers replicates to all the branches where receivers exist.
Multicast Applications
- One-to-many
- Many-to-many
- Many-to-one (rarely used)
Internet Group Management Protocol (IGMP) permit’s hosts to communicate their desire to receive multicast traffic to the multicast router on the LAN.
IGMP Versions
- IGMPv1 (old)
- IGMPv2
- IGMPv3 (design to work with Source-Specific Multicast)
Protocol-Independent Multicast (PIM) is a family of multicast routing protocols for IP networks. Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the revers path forwarding (RPF) check. PIM can leverage any unicast routing protocols.
PIM has four different configuration options
- PIM Dense Mode (rarely used – no RP required)
- PIM Sparse Mode
- Spare Mode
- Bidirectional PIM (Best for Many-to-Many applications)
- PIM Source-Specific Multicast
A Rendezvous Point (RP) is a router in a multicast network domain that acts as a shared root for a multicast shared tree.
A Designated Router (DR) is a router that will forward the PIM join message from the receiver to the RP.
A Designated Forwarder (DF) is a router that decide what packets need to be forwarded upstream toward the rendezvous point. (Used by Bidir PIM)
RP Deployment methods
- Static RP
- Bootstrap Router (BSR)
- Auto-RP
- Anycast-RP
- Phantom RP
- Embedded RP
Interdomain Multicast
Multiprotocol BGP (MBGP) + Multicast Source Discovery Protocol (MSDP)
PIM spare mode is used within a domain, domains are connected using MBGP (to exchange unicast routing table) and MSDP is used to peer between two RP’s in respective domain to exchange active source registered to RP’s in their respective domains.
**Be aware of multicast address overlap.
Rasesh Patel 