20 - Introducing Multicast Protocols

Question 1

__ is used to send the same data packets to multiple receivers.

Answer 1

multicast

Question 2

With multicast, routers process few packets because they receive only a single copy of the packet. This packet is then __ and sent on outgoing interface where there are receivers.

Answer 2

multiplied

Question 3

Because downstream routers perform packet multiplication and delivery to receivers, the sender or source of multicast traffic does not have to know the __ addresses of the receiver.

Answer 3

unicast

Question 4

__ transmission sends multiple copies of data, one copy for each receiver. __ transmission sends a single copy of data to multiple receivers.

Answer 4

unicast, multicast

Question 5

In multicast, the sender sends only one copy of a single data packet that is addressed to a group of receivers – a __.

Answer 5

multicast group

Question 6

Downstream multicast routers replicate and forward the data packet to all those branches where __ exist.

Answer 6

receivers

Question 7

Receivers express their interest in multicast traffic by registering at the first-hop router using __.

Answer 7

Internet Group Management Protocol

Question 8

Routers replicate the packet at any point where the network paths diverge and use ___techniques to ensure that the packet is forwarded to the appropriate downstream paths without routing loops.

Answer 8

RPF (Reverse-Path-Forwarding)

Question 9

What are some advantages of multicast?

Answer 9

• Network bandwidth is utilised more efficiently
• Network devices will have optimised performance due to fewer copies of data requiring forwarding and processing
• Greater possibility that multicast packets will arrive almost simultaneously at the receivers
• A whole range of new applications that were not possible on unicast will be available with multicast

Question 10

What are some disadvantages of multicast?

Answer 10

• Best-effort delivery results in occasional packet drops
• Packet loss may affect many multicast applications that operate in real time
• Heavy drops on voice applications result in jerky, missed speech patterns
• No transport layer congestion control may result in overall network degradation
• Duplicate packets my occasionally generated as multicast network topologies change
• UDP has no reliability mechanisms

Question 11

What are two of the most common models of IP multicast applications?

Answer 11

• One-to-many model, where one sender sends data to many receivers
• Many-to-many mode, where a host can simultaneously be a sender and receiver.

Question 12

Multicast IP addresses use the Class _ address space.

Answer 12

D

Question 13

What is the muticast local scope range – reserved by IANA for network protocol use

Answer 13

224.0.0.0-224.0.0.255

Question 14

What is the IP mulicast global scope range – allocated dynamically throughout the internet

Answer 14

224.0.1.0 – 238.255.255.255

Question 15

What is the IP multicast admin scope range – reserved for use inside private domains

Answer 15

239.0.0.0 – 239.255.255.255

Question 16

What is the IP multicast address for all hosts?

Answer 16

224.0.0.1

Question 17

What is the IP multicast address for all IPv4 routers?

Answer 17

224.0.0.2

Question 18

What is the IP multicast address for all PIMv2 routers?

Answer 18

224.0.0.13

Question 19

What are the IP multicast addresses that are used by unicast routing protocols?

Answer 19

224.0.0.5/6/9/10

Question 20

IP multicast service models consist of three main components:

Answer 20

• Senders send to a multicast address
• Receivers express an interest in a multicast address
• Routers deliver traffic from the senders to the receivers

Question 21

The primary purpose of __ is to permit hosts to communicate their desire to receive multicast traffic to the IP multicast router on the local network. This action, in turn, permits the IP multicast router to join the specified multicast group and to begin forwarding the multicast traffic onto the network segment.

Answer 21

IGMP

Question 22

With IGMPv1, multicast routers periodically (60-120 seconds) send member queries to all-hosts multicast address __ to solicit which multicast groups are active on the local network

Answer 22

224.0.0.1

Question 23

With IGMPv1, hosts wanting to receive specific multicast group traffic, send __

Answer 23

membership reports

Question 24

With IGMPv1, membership reports are sent with a TTL of _ to the multicast address of the group from which the host wants to receive traffic

Answer 24

1

Question 25

With IGMPv1, hosts either send reports:

Answer 25

o Asynchronously – when they want to first join a group o In response to membership queries, used to maintain the group in an active state so that traffic for the group remains forwarded to the network segment

Question 26

With IGMPv1, after a multicast router sends a membership query, there may be many hosts that are interested in receiving traffic from specified multicast groups. To suppress a membership report storm from all group members, a report ___ mechanism is used among group members, saving CPU time and bandwidth.

Answer 26

suppression

Question 27

With IGMPv1, because membership query and report packets have only local significance, the TTL of these packets is always set to _.

Answer 27

1

Question 28

With IGMPv1, if multicast traffic is forwarded on a local segment, there must be at least one __ member of that multicast group on a local segment

Answer 28

active

Question 29

Most of the changes between IGMPv1 and IGMPv2 were made primarily to address the issues of leave and join __ in addition to address ambiguities in the original protocol specification.

Answer 29

latencies

Question 30

What changes were made to IGMPv2?

Answer 30

Group-specific queries – allows the router to query its members only in a single group instead of all groups. This action is an optimised way to quickly find out if any members are left in a group without asking all groups for a report. Leave-group message – allows hosts to tell the router that they are leaving the group. Querier election mechanism – Unlike IGMPv1, v2 has a querier mechanism. The lowest unicast IP address of the of IGMPv2 capable routers will be elected as the querier. Query-interval response time – Controls the burstiness of reports. This time is set in queries to convey to the members how much time they must respond to a query with a report.

Question 31

IGMPv3 adds support for __, which enables a multicast receiver host to signal to a router the groups from which it wants to receive multicast traffic, and from which sources this traffic is expected. This membership information enables Cisco IOS software to forward traffic from only those sources from which receivers requested the traffic.

Answer 31

source filtering

Question 32

Multicast-capable routers create __ trees that control the path that IP multicast traffic takes through the network to deliver traffic to all receivers. The two basic types of multicast distribution trees are source trees and shared trees.

Answer 32

distribution

Question 33

The simplest form of a multicast distribution tree is a __ with its route at the source and branches forming a spanning 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).

Answer 33

source tree

Question 34

Unlike source trees that have their root at the source, __ use a single common root placed at some chosen point in the network. This shared root is called a rendezvous point (RP). Source traffic is sent towards the RP on a source tree. The traffic is then forwarded down the shared tree from the RP to reach all receivers.

Answer 34

shared trees

Question 35

In multicast forwarding, the source is sending traffic to an arbitrary group of hosts that are represented by a multicast group address. The multicast router must determine which direction is the __ direction and which is the __ direction. If there are multiple downstream paths, the router replicates the packet and forwards it down the appropriate downstream paths (best unicast route metric) – which is not necessarily all paths.

Answer 35

upstream ,downstream

Question 36

Forwarding multicast traffic away from the source, rather than to the receiver, is called ___. The basic idea of __ is that when a multicast packet is received on the router interface the router uses the source address to verify that the packet is not in a loop. The router checks the source IP of the packet against the routing table, and if the interface that the routing table indicates is the same interface on which the packet was received, the packet passes the __ check.

Answer 36

Reverse Path Forwarding (RPF)

Question 37

___ is a IP routing protocol-independent and can leverage whichever unicast routing protocols are used to populate the unicast routing table. __ uses this unicast routing information to perform the multicast forwarding function. Although __ is called a multicast routing protocol, it actually uses the unicast routing table to perform the RPF check function instead of building up a completely independent multicast routing table. Unlike other routing protocols, __ does not send and receive routing updates between routers.

Answer 37

Protocol Independent Multicast (PIM)

Question 38

There are two types of PIM multicast routing protocols, PIM __ mode and PIM __ mode.

Answer 38

dense, sparse

Question 39

___ uses a push model to flood multicast traffic to every corner of the network. This push model is a brute force method for delivering data to the receivers. This method would be efficient in certain deployments in which there are active receivers on every subnet in the network

Answer 39

PIM-DM (dense mode)

Question 40

__ operates independently of underlying unicast protocols. __ uses shared distribution tress routed at the RP, but it may also switch to the source-rooted distribution tree.

Answer 40

PIM-SM (sparse mode)

Question 41

PIM-SM is based on an explicit __ model. Therefore, the traffic is forward only to those parts of the network that need it.

Answer 41

pull

Question 42

PIM-SM uses an __ to coordinate the forwarding of multicast traffic from a source to its receivers. Senders register with the __ and send a single copy of multicast data through it to the registered receivers. Group members are joined to the shared tree by their local designated router. A shared tree that is built this way is always rooted at the __.

Answer 42

rendezvous point (RP)

Question 43

__ is appropriate for the wide-scale deployment of both densely and sparsely populate groups in the enterprise network. It is the optimate choice for all production networks, regardless of size and membership density.

Answer 43

PIM-SM

Question 44

A ___ is a router in a multicast network domain that acts as a shared root for a multicast shared tree. Any number of routers can be configured to work as __s, and they can be configured to cover different group ranges. For correct operation, every multicast router with a Protocol Independent Multicast (PIM) domain must be able to map a specific multicast group address to the same _.

Answer 44

rendezvous point (RP)

Question 45

It is possible to __ configure an RP for a multicast group range. The address of the RP must be configured on every routing in the domain.

Answer 45

statically

Question 46

The ___ is a mechanism for a router to learn RP information. It ensures that all routers in the PIM domain have the same RP cache as the __. It is possible to configure the __ to help select an RP set from the __ candidate RPs. The function of the __ is to broadcast the RP set to all routers in the domain

Answer 46

bootstrap router (BSR)

Question 47

__ is a non-proprietary method of defining RPs that can be used with third-party routers

Answer 47

BSR

Question 48

___ is a mechanism to automate distribution of RP information in a multicast network. The __ mechanism operates using two basic components, the candidate RPs and the RP-mapping agents.

Answer 48

Auto-RP