MULTICAST

Comparing Source Trees and Shared Trees

Both trees avoid multicast traffic loops and update dynamically. Source trees create optimal paths -Requires additional overhead Shared trees require minimum overall memory and complexity -Might not use optimal paths

IGMPv3 Lite

Cisco-proprietary transitional solution toward SSM. Supports SSM applications when hosts do not support IGMPv3. Requires Host Side IGMP Library (HSIL).

IP multicast uses

Class D addresses, which range from 224.0.0.0 to 239.255.255.255.

IGMPv3

Enables a multicast receiver to signal to a router the groups from which it wants to receive multicast traffic and from which sources to expect traffic. IGMPv3 messages: -Version 3 membership query -Version 3 membership report Receivers signal membership to a multicast host group in INCLUDE mode or EXCLUDE mode.

PIM Sparse-Dense Mode

Enables use of sparse or dense mode depending on available RP information -If RP information is learned, sparse mode is used

Internet Group Management Protocol (IGMP)

IGMP Versions: IGMP version 1 (IGMPv1) RFC 1112 IGMP version 2 (IGMPv2) RFC 2236 IGMP version 3 (IGMPv3) RFC 3376 IGMP version 3 lite (IGMPv3 lite)

IGMPv1

IGMP host membership query messages sent periodically to determine which multicast groups have members on the router's directly attached LAN's. IGMP query messages are addressed to the all-host group (224.0.0.1) and have an IP TTL equal to 1. When the end station receives an IGMP query message, the end station responds with a host membership report for each group to which the end station belongs.

IGMP Snooping

IP multicast constraining mechanism. Dynamically configures L2 ports to forward multicast traffic only to those ports with hosts wanting to receive it. Operates on multilayer switches. Examines IGMP join and leave messages.

IP Multicast Protocols

IP multicast uses its own routing, management, and Layer 2 protocols. Two important multicast protocols: -Protocol Independent Multicast (PIM) -Internet Group Management Protocol (IGMP)

Multicast Forwarding Trees

Multicast-capable routers create multicast distribution trees that control the path that IP multicast traffic takes through the network to deliver traffic to all receivers. The two types of distribution trees are: Source trees Shared trees

Protocol Independent Multicast (PIM)

PIM has two versions: 1 and 2 PIM has four modes of operation: -PIM dense mode -PIM sparse mode -PIM sparse-dense mode -PIM bidirectional

Automating Distribution of RP

PIM uses the following mechanisms to automate the distribution of the RP: Auto-RP -Automates distribution of group-to-RP mappings Bootstrap router (BSR) -Layer 3 device responsible for distributing RP -PIM version 2 only

Multicast IP Address Structure

Reserved link local addresses 224.0.0.0 to 224.0.0.255 Globally scoped addresses 224.0.1.0 to 238.255.255.255 Source-specific multicast addresses 232.0.0.0 to 232.255.255.255 Limited-scope addresses 239.0.0.0 to 239.255.255.255 GLOP addresses 233.0.0.0 to 233.255.255.255

Shared Trees

Shared trees use a single common root -Rendezvous Point (RP) Source traffic sent toward the RP. The traffic forwards down from the RP to all receivers

Reverse Path Forwarding (RPF)

The router looks up the source address in the unicast routing table to determine whether it arrived on the interface that is on the reverse path (lowest-cost path) back to the source. If the packet has arrived on the interface leading back to the source, the RPF check is successful, and the router replicates and forwards the packet to the outgoing interfaces. If the RPF check in the previous step fails, the router drops the packet and records the drop as an RPF failed drop.

Source Trees

The simplest form of a multicast distribution tree is a source tree with its root at the source and its branches forming a tree through the network to the receivers. Because this tree uses the shortest path through the network, it is also referred to as a shortest path tree (SPT).

IGMPv2

Types of IGMPv2 messages: -Membership query -Version 2 membership report -Leave report -Version 1 membership report The group-specific query message enables a router to transmit a specific query to one particular group. IGMPv2 also defines a leave group message for the hosts, which results in lower leave latency.

Methods of transmission:

Unicast Broadcast Multicast

Comparison and Compatibility of PIM

Version 1 and PIM Version 2 PIM version 2 is an IETF standard. -Interoperates with PIM-v1 and PIM-v2 routers -Version 2 downgrades if communicating with version 1 -BSR RP-distribution built-in PIM-v2

PIM Sparse Mode (PIM-SM)

When planning for multicast deployments, choose PIM-SM with IP under the following scenarios: -Many multipoint data streams -Few receivers in a group -Intermittent or busy traffic

IP multicast

is the transmission of IP data packets to a host group that is defined by a single IP address called a multicast IP address. traffic uses UDP as the transport layer protocol To avoid duplication, multicast routing protocols use reverse path forwarding (RPF).

PIM Dense Mode (PIM-DM) - Obsolete

rely on periodic flooding of the network with multicast traffic to set up and maintain the distribution tree. PIM relies on its neighbor information to form the distribution tree. PIM-DM uses a source distribution tree to forward multicast traffic, which is built by respective routers as soon as any multicast source begins transmitting. The figure illustrates an example of PIM-DM.