What transport protocol is used to deliver IP multicast traffic?

IP multicast traffic uses UDP as the trasport layer protocol. 

Because of the transport protocol, how is reliability handled in multicast environments?

Reliability in multicast is managed at the receiving client and by QoS in the network.

What is the IP range for multicast IP addresses?

224.0.00 to 239.255.255.255

Describe the structure of a multicast address

Multicast addresses consist of binary 1110 as the most significant bits (MSB) in the first octet, followed by a 28-bit group address. The last 28 bits of a Class D are unstructured.

What is the address range for link local destination addresses?

How do routers forward packets addressed to link local addresses?

Routers do not forward packets with link local addresses, because these packets are typically sent with a TTL value of 1. Network protocols use these addresses for automatic router discovery and to communicate important routing information.

What do addresses 224.0.0.1 and 224.0.0.2 signify?

What is the address range for globally scoped addresses?

224.0.1.0 to 238.255.255.255

What address range is reserved for source-specific multicast (SSM)?

Describe how Source-Specific Multicast (SSM) works.

In SSM, forwarding decisions are based on both group and source addresses, which is referred to as (S,G) (This defines "S" as the IP address of the source, and "G" as the multicast group address). The unique (S,G) is known as a channel

What are GLOP addresses?

GLOP addresses use 233.0.0.0 to 233.255.255.255 to statically define an organization that already has an autonomous system number reserved. The AS number is embedded into the second and third octets of the address range.

Describe limited-scope multicast addresses.

Limited-scope addresses range from 239.0.0.0 to 239.255.255.255. These addresses are constrained to a local group or organization. Edge routers typically deploy configurations with ACLs to prevent multicast traffic in this address range from flowing outside of an AS.

Describe the use of Reverse Path Forwarding (RPF) on a multicast router.

RPF is the mechanism that preforms an incoming interface check to determine whether to forward or drop an incoming multicast frame.

What are the 2 different types of distribution trees created by multicast-capable routers?

Source and shared trees

How does a source multicast distribution tree work?

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

Describe how a shared multicast distribution tree works.

Shared trees use a single common root placed at some chosen point in the network. This shared point is called a rendezvous point (RP). Source traffic is sent toward the RP on a shared tree. The traffic is then forwarded down the shared tree from the RP to reach all the receivers unless the receiver is located between the source and the RP, in which case the multicast traffic is serviced directly.

What are some of the advantages and disadvantages of using source multicast trees?

Source trees have the advantage of creating the optimal path between the source and the receiver. However, this optimization requires additional overhead because the routers maintain path information for each source.

What are some advantages and disadvantages of using shared multicast trees?

Shared trees have the advantage of requiring the minimum amount of state information in each router. The disadvantage of shared trees is that, under certain circumstances, the paths between the source and receivers might no be the optimal paths, which may introduce additional latency in packet delivery

What is the general purpose of a mulitcast routing protocol?

A multicast routing protocol is responsible for the construction of multicast delivery trees and enabling multicast packet forwarding

What is the general use of Protocol Independant Multicast (PIM)?

PIM is a multicast routing protocol that uses the PIM neighbor discovery mechanism to establish PIM neighbors using hello messages to the ALL-PIM-Routers multicast address (224.0.0.13)for building and maintaining PIM multicast distribution trees. Routers use PIM hello messages to elect the designated router (DR) for a multicast LAN network.

What are the 4 different modes of operation for PIM?

- PIM dense mode

- PIM sparse mode

- PIM spase-dense mode

- PIM bidirectional 

Describe how PIM dense mode (PIM-DM) forwards multicast traffic.

PIM-DM multicast routing protocols 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.

Describe how PIM sparse mode sends out multicast traffic.

PIM-SM protocols begin with an empty distribution tree and add branches only as the result of explicit requests to join the distribution. PIM-SM assumes that no hosts want the multicast traffic unless they specifically ask for it. When a sender wants to send data, it first does so to the RP. When the receiver wants to receive data, it registers with the RP. In PIM-SM, the shared tree mode can be switched to a source tree after a certain threshold to have the best route to the source.

Describe how PIM sparse-dense mode forwards multicast traffic.

PIM sparse-dense mode allows individual groups to use either sparse or dense mode depending on whether RP information is available for that group. If the router learns RP information for a particular group, sparse mode is used; otherwise, dense mode is used.

Describe how PIM bidirectional mode forwards multicast traffic.

Bidir-PIM can unconditionally forward source traffic toward the RP upstream on the shared tree without registering for sources as in PIM-SM. This allows traffic to be passed up the shared tree toward the RP.

How does PIM bidirectional mode avoid loops when forwarding multicast traffic up the shared tree?

To avoid muliticast packet loops, bidir-PIM introduces a mechanism called designated forwarder (DF) election, which establishes a loop-free SPT rooted at the RP. The DF is responsiable for forwarding muiltcast packets received on that network upstream to the RP. One DF exists for every RP of bidirectional groups.

What are the ways that PIM can use to automate the distribution of the RP?

It can use Auto-RP or Bootstrap router (BSR)

Describe how Auto-RP automates the distribution of the RP.

All router and L3 devices in the PIM network learn about the active group-to-RP mappings form the RP mapping agent by automatically joining the Cisco-RP-discovery mulitcast group (224.0.1.40). The RP mapping agent is the router that sends the authoritative discovery packets that notify other routers which group-to-RP mapping to use. The RP mapping agent sends this information every 60 seconds.

How do RP mapping agents discover which routers are possible canidate RPs?

Mapping agents use IP multicast to discover which routers in the network are possible candidate RPs by joining the Cisco-RP-announce group (224.0.1.39) to receive candidate RP announcements. Candidate RPs send RP-annouce multicast messages for the particular group every 60 senconds. The RP mapping agent uses the information contained in the announcement to create entries in group-to-RP cache.

Describe how a bootstrap router is used to distribute RPs.

Candidate RPs send candidate RP advertisements showing the group range from which each is responsible to the BSR, which stores this information in its local candidate RP cache. The BSR includes this information in its bootstrap messages and disseminates it to all PIM routers using 224.0.0.13 with a TTL of 1 in the domain hop-by-hop.

How is a bootstrap router choosen in a campus network?

BSR uses an election mechanism to select the BSR route from a set of candidate routers and MLSs inthe domain. The BSR election uses the BSR priority of the device contained in the BSR messages that flow hop-by-hop through the network. Each BSR device examines the messages and forwards it out all interfaces only if the message has either a higher BSR priority than the router's own BSR priority or has the same BSR priority but with a higher BSR IP address.

What happens to a router using PIM version 2 if it detects a PIM version 1 router?

The version 2 router will downgrade itself to version 1 until all version 1 routers have been shut down or upgraded.

What are the different types of hardware-based mulitcast switching and routing methods supported with IOS?

- Multicast multilayer switching (MMLS)

- CEF-based MMLS

- Multicast forwarding information base (MFIB) subsystem 

What are the multicast addresses for the following services?

- All-PIM-Routers
- GLOP Addresses
- Cisco-RP-Announce group
- Cisco-RP-Announce group
- Source-Specific Multicast
- Globally scoped addresses
- Link Local addresses
- Limited Scope addresses

- All-PIM-Routers - 224.0.0.13
- GLOP Addresses - 233.0.0.0 to 233.255.255.255
- Cisco-RP-Announce group - 224.0.1.39
- Cisco-RP-Announce group - 224.0.1.40
- Source-Specific Multicast - 232.0.0.0 to 232.255.255.255
- Globally scoped addresses - 224.0.1.0 to 238.255.255.255
- Link Local Addresses - 224.0.0.0 to 224.0.0.255
- Limited Scope addresses - 239.0.0.0 to 239.255.255.255