Multicast

CCNP Enterprise Nov 16, 2025

Allowing a single host to send a single stream of traffic to reach any number of destination hosts.

PIM-DM - flood and prune
PIM-SM - Explicit Join
IGMP v1-v3
IGMP snooping - layers 2 and 3

FF02::1 is the all-nodes multicast group within the scope of the local link. A packet with this destination address is received and processed by all IPv6-enabled interfaces.

The first 24 bits of a multicast MAC address are always 01:00:5E.

Link-local non-routable 224.0.0.0 to 224.0.0.255 (reserved for local network use, has TTL = 1)

The multicast range 239.0.0.0/8 is equivalent to private addresses.

Multicast addresses in IPv6 use the prefix FF00::/8

well-known IPv4 multicast addresses


224.0.0.1	All Hosts
224.0.0.2	All Routers
224.0.0.4	DVMRP Router
224.0.0.5	OSPF Routers
224.0.0.6	OSPF Designated routers
224.0.0.9	RIPv2 Routers
224.0.0.10	EIGRP Routers
224.0.0.12	DHCP server/relay agent
224.0.0.13	All PIM Routers
224.0.0.18	VRRP
224.0.0.19	All IGMPv3 Routers
224.0.0.102	HSRP
224.0.0.107	PTP v2
224.0.0.251	mDNS
224.0.0.252	LLMNR
224.0.0.253	Teredo
224.0.1.39	RP announce group
224.0.1.40	RP discovery group

well-known IPv6 multicast addresses


ff02::1	All Hosts
ff02::2	All Routers
ff02::5	OSPF Routers
ff02::6	OSPF Designated routers
ff02::8	IS-IS Routers
ff02::9	RIP Routers
ff02::a	EIGRP Routers

well-known Ethernet multicast addresses


01-80-C2-00-00-00	STP 802.1D
01-00-0C-CC-CC-CC	CDP, VTP
01:00:0C:CC:CC:CD	Cisco per-VLAN STP

Source Trees

Routers examine the Source IP address and the Multicast group. Create an entry to the multicast routing table.

All routers are aware of the stream. Not scalable for large networks.

Shared Trees

Multicast streams register with the RP router. Other routers have a default gateway to the RP.

Client wants to subscribe to a stream, router will ask the RP, RP will act as a proxy.

Router can switch back to teh source tree model if more efficient, once it has source from RP.

Protocol Independent Multicast (PIM) Dense Mode

Relies on unicast routing table to get around network.

Source Tree model for small networks.

Enabled on all required interfaces on all routers

ip multicast-routing
int se0/0
  ip pim dense-mode

All routers will get multicast stream and pass it on to all other routers.

Routers will prune back if no clients are requesting the stream. Resets itself every 3 minutes.

Protocol Independent Multicast (PIM) Sparse Mode

Shared tree with a Rendezvous Point. Pull mode.

Everything goes to RP first, once router has the source may change if more efficant path to source.

sparse-dense-mode - runs in both modes, dense mode if no RP. Auto RP needs this mode.

Can use an access list to use a different RP for groups.

Auto RP to advise the RP without static configuration on all routers. Use a loopback interface.

scope is TTL of the RP advertisement. Default every 60 seconds.

Discovery router (mapping agent) collects all the RP advertisements and sends them out

ip multicast-routing
int se0/0
  ip pim sparse-dense-mode
		
show ip pim interfaces
show ip mroute

#Test without multicast server
int e0
  ip igmp join-group 230.140.100.1

ping 230.140.100.1

# Add RP on all routers as static configuration
ip pim rp-add 192.168.1.3
# Auto RP
ip pim send-rp-announce s0/0.1 scope 15 
ip pim send-rp-discovery scope 15

ip pim accept-rp #add to all routers

show ip pim rp map

#Restrict multicast traffic
int se0/1
  ip multicast ttl-threshold 255
  ip multicast boundary 1