Chapter 13 - Multicast

Question 1

designated router (DR)

Answer 1

A PIM-SM router that is elected in a LAN segment when multiple PIM-SM routers exist to prevent the sending of duplicate multicast traffic into the LAN or the RP.

Question 2

downstream

Answer 2

Away from the source of a tree and toward the receivers.

Question 3

downstream interface

Answer 3

An interface that is used to forward multicast traffic down the tree, also known as the outgoing interface (OIF).

Question 4

first-hop router (FHR)

Answer 4

A router that is directly attached to the source, also known as the root router. It is responsible for sending register messages to the RP.

Question 5

incoming interface (IIF)

Answer 5

The only type of interface that can accept multicast traffic coming from the source. It is the same as the RPF interface.

Question 6

IGMP snooping

Answer 6

A mechanism to prevent multicast flooding on a Layer 2 switch.

Question 7

Internet Group Management Protocol (IGMP)

Answer 7

The protocol used by receivers to join multicast groups and start receiving traffic from those groups.

Question 8

last-hop router (LHR)

Answer 8

A router that is directly attached to the receivers, also known as a leaf router. It is responsible for sending PIM joins upstream toward the RP or to the source after an SPT switchover.

Question 9

Multicast Forwarding Information Base (MFIB)

Answer 9

A forwarding table that derives information from the MRIB to program multicast forwarding information in hardware for faster forwarding.

Question 10

Multicast Routing Information Base (MRIB)

Answer 10

A topology table that is also known as the multicast route table (mroute), which derives from the unicast routing table and PIM.

Question 11

multicast state

Answer 11

The traffic forwarding state that is used by a router to forward multicast traffic. The multicast state is composed of the entries found in the mroute table (S, G, IIF, OIF, and so on).

Question 12

outgoing interface (OIF)

Answer 12

An interface that is used to forward multicast traffic down the tree, also known as the downstream interface.

Question 13

outgoing interface list (OIL)

Answer 13

A group of OIFs that are forwarding multicast traffic to the same group.

Question 14

Protocol Independent Multicast (PIM)

Answer 14

A multicast routing protocol that routes multicast traffic between network segments. PIM can use any of the unicast routing protocols to identify the path between the source and receivers.

Question 15

rendezvous point (RP)

Answer 15

A single common root placed at a chosen point of a shared distribution tree. In other words, it is the root of a shared distribution tree known as a rendezvous point tree (RPT).

Question 16

rendezvous point tree (RPT)

Answer 16

Also known as a shared tree, a multicast distribution tree where the root of the shared tree is not the source but a router designated as the rendezvous point (RP).

Question 17

Reverse Path Forwarding (RPF) interface

Answer 17

The interface with the lowest-cost path (based on administrative distance [AD] and metric) to the IP address of the source (SPT) or the RP.

Question 18

RPF neighbor

Answer 18

The PIM neighbor on the RPF interface.

Question 19

shortest path tree (SPT)

Answer 19

A router’s view of the topology to reach all destinations in the topology, where the router is the top of the tree, and all of the destinations are the branches of the tree. In the context of multicast, the SPT provides a multicast distribution tree where the source is the root of the tree and branches form a distribution tree through the network all the way down to the receivers. When this tree is built, it uses the shortest path through the network from the source to the leaves of the tree.

Question 20

upstream

Answer 20

Toward the source of a tree, which could be the actual source with a source-based tree or the RP with a shared tree. A PIM join travels upstream toward the source.

Question 21

upstream interface

Answer 21

The interface toward the source of the tree. Also known as the RPF interface or the incoming interface (IIF).