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

There are three different PIM (Protocol Independent Multicast) modes.

• dense mode – havving multiple clients, which are tightly spaced together, it’s implicit for all devices in the PIM domain that they are joined to the multicast domain, if they don’t want to receive the multicast stream, they have to send a „prune“ message. It’s called the „flood and prune“ behavior
• sparse mode – devices have to send a join message, without they will not receive the multicast stream. It’s designed for networks which have clients that are few and far between. It’s called an „explicit join“ mechanism. It depends on a central RP (rendezvous point“, which is organizing forwarding in the multicast domain
• sparse-dense mode – is a combination of both. if there is an RP configured it will use sparse mode. But if the RP fails or is not reachable any more, the router will fall back to dense mode. If you want to prohibit this, there is an „no ip pim dense fallback“

• 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

Sparse-Dense-Mode

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.

Source:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/himc_c/mcbcncpt.htm#wp1075142

http://dast.nlanr.net/Projects/Iperf/

IP Multicast is defined in RFC 1112/2236(IGMPv2).

Ip Multicast can send traffic to a single address and does not care about the receiving hosts. Only one destination address is needed and all hosts listening to the stream or host that have registred can receive the datastream. It does support dynamic meberships to groups. So clients can themselfes register for the stream.

One multicast address can carry multiple streams. It uses UDP as transport protocol.

Address range:

Class D 224.0.0.0 – 239.255.255.255

The range from 224.0.0.0 to 224.0.0.255 is reserved for routing protocols and other types of protocols.

Static Addresses (local scope):

• 224.0.0.1 all hosts on a subnet
• 224.0.0.2 all routers on a subnet
• 224.0.0.4 Distance Vector Multicast Routing Protocols (DVMRP)
• 224.0.0.5 OSPF routers
• 224.0.0.6 OSPF designated routers
• 224.0.0.9 RIP Version 2 routers
• 224.0.0.10 EIGRP
• 224.0.0.13 Protocol independent Multicast (PIM)

Global scope addresses:

224.0.1.0 – 238.255.255.255

Administratively scoped:

239.0.0.0 – 239.255.255.255

Internet Multicast address range reserved by IANA (lower 23 bits):

0100.5e00.000 – 0100.5e7f.ffffAll Multicast addresses use the 01.00.5e in their multicast address.

Source:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ipmulti.htm#xtocid1

http://www.iana.org/assignments/multicast-addresses

• Unicast – individual packets are send to every requesting address, so the number of clients is fixed to the bandwidth the streaming applications needs

• Broadcast – traffic is send to one broadcast address and then forwarded to the entire broadcast domain, you can ping for example a broadcast address and see, that all hosts receive this ping. But broadcast are limitted to layer 3 boarders

• Multicast – sending a packet to a predefined multicast address, receiving hosts, can register for receiving streams in groups

1. enable ip multicast routing with „ip multicast-routing“
2. enable PIM on an interface
3. configure a rendezvous point

Here for example you use sparse-mode
# ip multicast-routing

# int e0/0

# ip pim sparse-mode

# ip igmp join-group 224.0.33.0