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CCNA IP Multicast Questions

58 questions · IP Multicast · All types, answers revealed

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1
MCQmedium

A network engineer is deploying IP multicast in an OSPF-based enterprise network. The network uses PIM sparse mode with a static RP. The engineer notices that multicast traffic from a source to a group is not reaching receivers in a remote subnet, even though the RP is reachable and the receivers have sent IGMP joins. The engineer checks the multicast routing table on the last-hop router and sees that the (S,G) entry is present, but the outgoing interface list (OIL) is empty. What is the most likely reason for the empty OIL?

A.The RP is not configured on the last-hop router.
B.The multicast source is not registered with the RP.
C.PIM dense mode is enabled on the last-hop router.
D.The TTL of the multicast packets is too low.
AnswerA

Correct because without the RP configured, the router cannot send a PIM join to the RP, so the OIL remains empty.

Why this answer

In PIM sparse mode, the last-hop router must send a PIM join toward the RP to join the shared tree. If the RP is reachable but the join is not being sent because the router does not know the RP or the group-to-RP mapping, the OIL remains empty.

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2
Drag & Dropmedium

Drag and drop the steps of IGMP v3 SSM membership report process into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

IGMPv3 SSM membership reports are sent by hosts to request traffic from specific sources. The host first sends a Membership Report listing desired (S,G) pairs. The router processes the report, updates its multicast routing table, and then sends PIM (S,G) Joins toward the source.

The source forwards traffic, which is then delivered to the host.

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3
MCQmedium

A network engineer is troubleshooting multicast video distribution across an enterprise campus. The multicast source is connected to a switch that is the PIM Designated Router (DR) on a multi-access segment. Receivers in a different VLAN report that they are not receiving the multicast stream, although the DR shows the correct (S,G) entry. The engineer checks the RPF neighbor for the source and notices that the unicast route to the source points to a different interface than the one where the multicast stream is received. What is the most likely cause of the issue?

A.The DR is not configured as the RP (Rendezvous Point).
B.The multicast stream is arriving on an interface that is not the RPF interface for the source.
C.The switchport connected to the source is not configured as a trunk.
D.IGMP snooping is disabled on the receiver VLAN.
AnswerB

Correct because multicast forwarding requires the incoming interface to match the unicast RPF interface; a mismatch causes the packet to be dropped.

Why this answer

Multicast forwarding requires RPF check: the incoming interface for multicast traffic must match the unicast reverse path to the source. If the unicast route points to a different interface, the RPF check fails and the multicast packet is dropped, even if the DR is correct.

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4
Drag & Dropmedium

Drag and drop the steps of PIM DM (Dense Mode) flood and prune steps into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

PIM Dense Mode initially floods multicast traffic to all PIM-enabled interfaces. Routers that do not have interested receivers send Prune messages upstream. The upstream router then stops forwarding traffic on the pruned interface.

If a new receiver appears, a Graft message re-adds the branch.

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5
MCQmedium

A network engineer runs the following command on Router R8: R8# show ip mroute count IP Multicast Statistics Group: 239.4.4.4, Source: 10.0.0.9 Packets: 1500, Bytes: 1200000, Average rate: 8000 pps, 5 sec rate: 0 pps Group: 239.5.5.5, Source: 10.0.0.10 Packets: 0, Bytes: 0, Average rate: 0 pps, 5 sec rate: 0 pps Based on this output, what can be concluded?

A.Multicast traffic is flowing for group 239.4.4.4.
B.Multicast traffic is flowing for group 239.5.5.5.
C.Both groups are receiving traffic.
D.The source for group 239.4.4.4 is 10.0.0.10.
AnswerA

The packet and byte counts are non-zero, indicating traffic.

Why this answer

The 'show ip mroute count' output shows multicast statistics for two groups. For group 239.4.4.4, there are 1500 packets and 1200000 bytes, with an average rate of 8000 pps. For group 239.5.5.5, there are no packets.

This indicates that multicast traffic is flowing for the first group but not for the second. The correct answer is that multicast traffic is being received for group 239.4.4.4.

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6
Matchingmedium

Drag and drop each PIM message type on the left to its matching function on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Discovers and maintains PIM neighbors

Requests to join a multicast group and receive traffic

Requests to leave a multicast group and stop receiving traffic

Resolves duplicate forwarding on a multi-access network

Elects the RP in PIM Sparse Mode

Why these pairings

PIM Hello discovers neighbors; Join requests to join a group; Prune requests to leave a group; Assert resolves duplicate forwarding on a multi-access network.

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7
MCQhard

A network engineer is troubleshooting multicast connectivity in a large enterprise. The network uses PIM sparse mode with Auto-RP. The engineer notices that some routers are not receiving the RP mapping for a particular group. The engineer checks the Auto-RP mapping agent and sees that it is sending RP announcements, but the routers that are missing the mapping are not in the same PIM domain. What is the most likely reason?

A.The routers missing the mapping do not have 'ip pim autorp listener' configured.
B.The mapping agent is not configured as a candidate RP.
C.The TTL of the RP announcements is set too low.
D.The routers missing the mapping have PIM dense mode enabled.
AnswerA

Correct because Auto-RP uses reserved multicast groups; without this command, routers may not process the RP announcements.

Why this answer

Auto-RP uses multicast groups 224.0.1.39 and 224.0.1.40. Routers must be configured to listen to these groups using the 'ip pim autorp listener' command, especially if they are not in the same PIM domain or if PIM is not enabled on all interfaces.

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8
Drag & Dropmedium

Drag and drop the steps of multicast RP discovery using BSR into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

BSR election occurs first, then the BSR collects RP announcements, creates an RP-set, and floods it to all routers; each router then uses the hash function to select the RP for a group.

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9
Drag & Dropmedium

Drag and drop the steps of Multicast RP discovery using BSR into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

In BSR, candidate RPs announce themselves to the BSR. The BSR collects these announcements and distributes a list of RPs via Bootstrap messages. Routers then use a hash function to select the RP for each group.

The RP must be reachable for the process to work.

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10
Matchingmedium

Drag and drop each multicast tree type on the left to its matching description on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Tree rooted at the source, uses optimal path to each receiver

Shared tree rooted at the RP, used in PIM Sparse Mode

Shared tree that allows multicast traffic to flow in both directions

A tree rooted at the source of the multicast traffic

A tree rooted at the RP, shared by all sources for a given group

Why these pairings

SPT is the shortest path from source to receivers; RPT is a shared tree rooted at the RP; Bidirectional tree allows traffic to flow both ways; Source tree is a tree rooted at the source; Shared tree is a tree rooted at the RP.

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11
MCQeasy

An engineer is configuring multicast on a Cisco router. The router receives multicast traffic from a source on interface GigabitEthernet0/0 and needs to forward it to receivers on interface GigabitEthernet0/1. The engineer enables PIM sparse mode on both interfaces and configures a static RP. However, the router does not create a multicast routing entry for the (S,G) pair. What is the most likely missing configuration?

A.The global command 'ip multicast-routing' is not configured.
B.The interface GigabitEthernet0/0 is not configured with an IP address.
C.The RP address is not reachable from the router.
D.The router is not configured as a candidate RP.
AnswerA

Correct because this command is required to enable multicast routing on the router.

Why this answer

For multicast routing to work, the 'ip multicast-routing' command must be enabled globally. Without it, the router will not create multicast forwarding entries, even if PIM is enabled on interfaces.

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12
Multi-Selecteasy

Which three statements about multicast group addresses and Layer 2 mapping are true? (Choose three.)

Select 3 answers
A.The multicast MAC address is derived by placing the lower 23 bits of the multicast IP address into the OUI 01-00-5E.
B.Multiple multicast IP addresses can map to the same multicast MAC address.
C.The multicast IP address 224.0.0.1 maps to the MAC address 01-00-5E-00-00-01.
D.The multicast IP address range 224.0.0.0/24 is reserved for global scope and can be routed across the internet.
E.The multicast MAC address 01-00-5E-00-00-05 corresponds to the IP address 224.0.0.5.
AnswersA, B, C

Correct because the standard mapping takes the last 23 bits of the IP multicast group address and copies them into the last 23 bits of the MAC address 01-00-5E-00-00-00 (with the high-order bit of the MAC set to 0).

Why this answer

Multicast IP addresses in the 224.0.0.0/4 range map to a Layer 2 MAC address range. The mapping is not unique, leading to possible overlap. Well-known addresses like 224.0.0.1 are used for local link communication and are not routable.

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13
MCQhard

A network engineer runs the following command on Router R4: R4# show ip pim rp mapping PIM Group-to-RP Mappings This system is an RP (Auto-RP) This system is an RP (BSR) Group(s) 224.0.0.0/4 RP 10.0.0.2 (?), v2v1 Info source: 10.0.0.2 (?), elected via Auto-RP, expires in 00:01:30 RP 10.0.0.3 (?), v2v1 Info source: 10.0.0.3 (?), elected via BSR, expires in 00:02:00 Based on this output, what can be concluded?

A.Only Auto-RP is being used for RP mapping.
B.Only BSR is being used for RP mapping.
C.Both Auto-RP and BSR are configured, causing multiple RP mappings.
D.The router is not an RP.
AnswerC

The output shows two different RPs for the same group range, learned from different protocols.

Why this answer

The output shows that this router is configured as an RP for both Auto-RP and BSR. There are two RPs for the same group range: one learned via Auto-RP (10.0.0.2) and one via BSR (10.0.0.3). The router itself is also an RP.

This indicates that both Auto-RP and BSR are configured, which can cause conflicts. The correct answer is that both Auto-RP and BSR are active, leading to multiple RP mappings.

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14
MCQhard

An engineer is configuring multicast on a Cisco router running IOS-XE. The network uses PIM sparse mode with a static RP at 10.1.1.1. The engineer enters the command 'ip pim rp-address 10.1.1.1' but multicast traffic is not being forwarded. Upon verification, the engineer sees that the RP is reachable via OSPF, but the 'show ip pim rp mapping' command does not list any RP for the group. What is the most likely cause?

A.The RP address is not reachable via the unicast routing table.
B.The command 'ip pim rp-address 10.1.1.1' must include an access-list to define the group range.
C.PIM sparse mode must be enabled on all interfaces first.
D.The router must be configured as a candidate RP using 'ip pim send-rp-announce'.
AnswerB

Correct because the RP mapping requires an access-list to specify the groups; without it, the RP is not associated with any group.

Why this answer

The 'ip pim rp-address' command requires an access-list to specify which groups the RP serves. Without the access-list, the command is incomplete and the RP mapping is not applied, even though the RP is reachable.

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15
MCQmedium

A network engineer issues the following command on Router R5: R5# show ip pim interface Interface PIM Nbrs Hello DR DR Count Intvl Prior GigabitEthernet0/0 on 2 30 1 10.1.1.1 GigabitEthernet0/1 on 1 30 1 10.2.2.2 Loopback0 on 0 30 1 10.3.3.3 Based on this output, what can be concluded?

A.The DR on GigabitEthernet0/0 is 10.1.1.1.
B.The DR on GigabitEthernet0/1 is the local router.
C.PIM is disabled on Loopback0.
D.The hello interval on GigabitEthernet0/0 is 60 seconds.
AnswerA

The DR column shows 10.1.1.1 for that interface.

Why this answer

The 'show ip pim interface' output shows that GigabitEthernet0/0 has 2 PIM neighbors, a hello interval of 30 seconds, DR priority of 1, and the DR is 10.1.1.1. GigabitEthernet0/1 has 1 neighbor and its DR is 10.2.2.2. Loopback0 has no neighbors and its DR is the router's own IP.

The correct answer is that the DR on GigabitEthernet0/0 is 10.1.1.1, which is not the local router (since the local router's IP is not shown, but it is likely different).

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16
MCQmedium

Examine the following configuration on a Cisco IOS-XE router: ip multicast-routing distributed ! interface GigabitEthernet0/0 ip address 192.168.1.1 255.255.255.0 ip pim sparse-dense-mode ip igmp version 2 ! Which statement about this configuration is true?

A.The interface will operate in dense-mode for all multicast groups because no RP is configured.
B.The router will only support IGMPv2, and IGMPv3 queries will be ignored.
C.Multicast routing is enabled with distributed switching, and the interface will use sparse-mode if an RP is known for the group, otherwise dense-mode.
D.The configuration is invalid because 'ip multicast-routing distributed' is not a valid command.
AnswerC

Correct. The 'ip multicast-routing distributed' enables multicast routing with CEF-based distributed switching. Sparse-dense-mode adapts based on RP knowledge.

Why this answer

The 'ip multicast-routing distributed' command enables multicast routing with support for distributed switching (CEF). The interface is configured with PIM sparse-dense-mode, which allows the interface to operate in dense-mode if no RP is known for the group, or in sparse-mode if an RP is known. IGMPv2 is used for group membership.

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17
Drag & Dropmedium

Drag and drop the steps of Multicast RP discovery using Auto-RP into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

Auto-RP uses a mapping agent to discover RPs. Candidate RPs announce their services to a well-known group (224.0.1.39). The mapping agent collects these announcements and sends RP-to-group mappings to another group (224.0.1.40).

Routers then learn the RP for each group.

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18
Multi-Selectmedium

Which two statements about PIM sparse mode are true? (Choose two.)

Select 2 answers
A.PIM sparse mode uses an explicit join model to receive multicast traffic.
B.PIM sparse mode routers always use the shortest path tree (SPT) immediately after the first packet is received.
C.PIM sparse mode builds a shared tree rooted at the rendezvous point (RP).
D.PIM sparse mode uses a flood-and-prune mechanism to distribute multicast traffic.
E.PIM sparse mode requires the use of a bootstrap router (BSR) to operate.
AnswersA, C

Correct because in PIM sparse mode, receivers must explicitly join via PIM Join messages toward the RP.

Why this answer

PIM sparse mode uses an explicit join model where routers send PIM Join messages toward the RP to join a multicast group. It builds a shared tree (RP-tree) initially, and optionally switches to a source tree (SPT) when traffic exceeds a threshold. PIM dense mode uses flood-and-prune, not sparse mode.

PIM-BSR is one method for RP distribution, but not a requirement for sparse mode operation.

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19
MCQmedium

An engineer is configuring multicast on a Cisco switch running IOS. The switch is acting as the IGMP querier for a VLAN. The engineer notices that multicast traffic is being flooded to all ports in the VLAN, even though only a few receivers have joined the group. The engineer checks the IGMP snooping configuration and sees that IGMP snooping is enabled globally and on the VLAN. What is the most likely cause of the flooding?

A.The IGMP querier is not elected on the VLAN.
B.The multicast source is connected to a trunk port.
C.The switch has PIM enabled on the VLAN interface.
D.The receivers are using IGMPv3.
AnswerA

Correct because without a querier, IGMP snooping cannot learn group memberships, causing the switch to flood multicast traffic.

Why this answer

IGMP snooping relies on the switch seeing IGMP membership reports. If the switch does not see the reports because the querier is not elected or because the reports are not forwarded to the switch CPU, the switch will flood multicast traffic to all ports.

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20
Matchingmedium

Drag and drop each multicast tree type on the left to its matching description on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

A source-specific multicast tree rooted at the source

A shared multicast tree rooted at the RP

A shared tree where traffic flows both toward and away from the RP

A shared tree for group G, used in PIM SM before switching to SPT

A source-specific tree for source S and group G

Why these pairings

SPT is a source-specific tree rooted at the source; RPT is a shared tree rooted at the RP; Bidir tree is a shared tree used in Bidir PIM; (*,G) tree is a shared tree for all sources; (S,G) tree is a source-specific tree.

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21
Drag & Dropmedium

Drag and drop the steps of IGMP v3 SSM membership report process into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

In IGMPv3 SSM, the host first sends a membership report with (S,G) inclusion, the querier processes it, updates its state, and then triggers PIM (S,G) join toward the source.

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22
Multi-Selecthard

Which two statements about multicast RPF check are true? (Choose two.)

Select 2 answers
A.The RPF check uses the unicast routing table (or a dedicated multicast routing table) to determine the best path back to the multicast source.
B.If the RPF check fails, the multicast packet is dropped to prevent routing loops.
C.The RPF check is performed only on the first packet of a multicast stream; subsequent packets are forwarded without verification.
D.The RPF check can be overridden by configuring a static multicast route (mroute) that points to a different incoming interface.
E.The RPF check is only relevant for PIM-SM and not for PIM-DM.
AnswersA, B

Correct because the RPF check compares the source IP address of the multicast packet against the routing table (RIB or MRIB) to find the outgoing interface toward the source; the packet is accepted only if it arrives on that interface.

Why this answer

RPF check is a fundamental loop prevention mechanism in multicast. It verifies that the incoming interface of a multicast packet is the same interface the router would use to reach the source. If the check fails, the packet is dropped.

RPF can be influenced by static mroutes and is performed on all multicast packets, not just data.

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23
MCQmedium

A network engineer executes the following command on Router R3: R3# show ip igmp groups 239.2.2.2 IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter 239.2.2.2 GigabitEthernet0/0 1d04h 00:02:10 192.168.1.100 Based on this output, what can be concluded?

A.The multicast group is being sourced from 192.168.1.100.
B.A host at 192.168.1.100 has joined group 239.2.2.2.
C.The router is the RP for this group.
D.The group is using IGMP version 3.
AnswerB

The last reporter indicates the host that sent the most recent IGMP membership report for this group.

Why this answer

The 'show ip igmp groups' output shows that group 239.2.2.2 is present on interface GigabitEthernet0/0, with the last reporter being 192.168.1.100. The uptime is 1 day and 4 hours, and the expiry timer is about 2 minutes. This indicates that there is at least one IGMP host on that subnet interested in the group.

The correct answer is that a host at 192.168.1.100 has sent an IGMP report for this group.

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24
MCQeasy

A network engineer is configuring multicast on a Cisco router that connects to a multi-access network. The engineer wants to ensure that only one router forwards multicast traffic onto the segment to avoid duplication. The engineer enables PIM on the interface. However, multicast traffic is still being duplicated on the segment. What is the most likely reason?

A.Both routers have the same DR priority and the DR election has not completed.
B.The interface is configured as a passive interface under OSPF.
C.IGMP snooping is disabled on the switch connecting the routers.
D.The multicast group is in the 224.0.0.0/24 range.
AnswerA

Correct because if the DR priority is equal, the router with the higher IP address becomes DR; if not elected, both may forward.

Why this answer

On a multi-access network, PIM elects a Designated Router (DR) to forward multicast traffic. If the DR election fails or if both routers have the same DR priority, both may forward traffic, causing duplication.

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25
MCQhard

A network engineer issues the following command on Router R9: R9# show ip pim bsr-router PIMv2 Bootstrap Router (BSR) information This system is the Bootstrap Router (BSR) BSR address: 10.0.0.11 Uptime: 1w2d, BSR priority: 0, Hash mask length: 30 Next bootstrap message in 00:00:45 Based on this output, what can be concluded?

A.This router is the elected BSR.
B.This router is a candidate BSR but not elected.
C.The BSR priority is 192.
D.The hash mask length is 32.
AnswerA

The output states 'This system is the Bootstrap Router'.

Why this answer

The 'show ip pim bsr-router' output shows that this router is the BSR with address 10.0.0.11, priority 0, and hash mask length 30. The next bootstrap message will be sent in 45 seconds. The hash mask length of 30 means that the group-to-RP mapping uses a 30-bit mask for hashing.

The correct answer is that the BSR is elected and operational.

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26
Matchingmedium

Drag and drop each PIM mode on the left to its matching traffic distribution method on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Uses explicit join messages to build a shared tree, then can switch to shortest-path tree

Floods multicast traffic on all interfaces, then prunes branches that do not want it

Uses (S,G) state only; receivers must know the source address via IGMPv3

Uses a shared tree for both sources and receivers; no source-specific tree; uses designated forwarder to prevent loops

Allows interface to operate in sparse or dense mode per group

Why these pairings

PIM Sparse Mode uses explicit join to build shared tree then optionally switch to SPT; PIM Dense Mode floods and prunes; PIM SSM uses exclusively source-specific trees; PIM Bidir uses a shared tree with no source-specific tree and a designated forwarder to prevent loops.

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27
Multi-Selecthard

Which three statements about multicast RP (Rendezvous Point) are true? (Choose three.)

Select 2 answers
A.The RP is used only in PIM sparse mode and is the root of the shared distribution tree.
B.A single RP can serve multiple multicast groups, and multiple RPs can be configured for different group ranges.
C.The RP must be the first-hop router for all multicast sources in the network.
D.The RP must be directly connected to all multicast receivers.
E.In PIM dense mode, the RP is used to limit multicast flooding.
AnswersA, B

Correct because the RP is a key component of PIM sparse mode, serving as the root of the shared tree (RP-tree).

Why this answer

The RP is a central router in PIM sparse mode that acts as the meeting point for sources and receivers. Sources register with the RP, and receivers join via the RP. Multiple RPs can be configured for different groups using Auto-RP or BSR.

The RP is not required to be the first-hop router for the source; sources can be anywhere in the network. The RP does not need to be directly connected to receivers; it only needs IP reachability. PIM dense mode does not use an RP.

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28
Drag & Dropmedium

Drag and drop the steps of MSDP peering for inter-domain multicast into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

MSDP peers first establish a TCP connection, then exchange SA messages to advertise active sources; the remote RP receives the SA, creates (S,G) state, and forwards join toward the source.

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29
MCQeasy

Which PIM mode requires a rendezvous point (RP) to function?

A.PIM Dense-Mode
B.PIM Sparse-Mode
C.PIM Sparse-Dense-Mode
D.PIM Bidirectional
AnswerB

Correct. Sparse-mode requires an RP to manage group membership.

Why this answer

PIM sparse-mode (SM) requires an RP to act as a meeting point for receivers and sources. Dense-mode uses flood-and-prune without an RP, and bidirectional PIM also uses an RP but with a different mechanism.

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30
MCQmedium

Examine the following configuration snippet: ip pim send-rp-announce Loopback0 scope 10 group-list 10 ip pim send-rp-discovery scope 10 access-list 10 permit 239.0.0.0 0.255.255.255 ! interface Loopback0 ip address 192.168.0.1 255.255.255.255 ip pim sparse-mode ! What is the purpose of this configuration?

A.The router will act as both a candidate RP for groups 239.0.0.0/8 and a mapping agent for Auto-RP within a scope of 10 hops.
B.The router will only act as a mapping agent and will not advertise itself as an RP.
C.The router will use the IP address of GigabitEthernet0/0 as the RP address.
D.The router will only accept RP announcements from other routers within 10 hops.
AnswerA

Correct. The router is configured as both a candidate RP and a mapping agent, with a TTL scope of 10.

Why this answer

This configures the router as an Auto-RP mapping agent and candidate RP. The 'send-rp-announce' command advertises this router as a candidate RP for groups matching ACL 10 (239.0.0.0/8) with a TTL scope of 10. The 'send-rp-discovery' command makes the router act as a mapping agent, listening for RP announcements and sending RP-discovery messages.

The loopback interface is used as the RP address.

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31
MCQhard

A network engineer is configuring PIM sparse mode in a network that uses a Bootstrap Router (BSR) for RP discovery. The engineer has configured a candidate BSR and candidate RPs. However, some routers in the network are not learning the RP set. The engineer checks the BSR and sees that it is receiving candidate RP advertisements, but the BSR messages are not being forwarded to all routers. What is the most likely cause?

A.PIM is not enabled on all interfaces between the BSR and the other routers.
B.The candidate BSR priority is set too low.
C.The candidate RPs are not in the same OSPF area as the BSR.
D.The BSR is not configured as a candidate RP.
AnswerA

Correct because BSR messages rely on PIM to flood; without PIM on intermediate interfaces, the messages are dropped.

Why this answer

BSR messages are flooded hop-by-hop using PIM. If PIM is not enabled on all interfaces between the BSR and the other routers, the BSR messages will not be forwarded, preventing RP discovery.

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32
MCQmedium

A network engineer issues the following command on Router R2: R2# show ip mroute 239.1.1.1 IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group session, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 239.1.1.1), 00:03:45/00:02:15, RP 10.0.0.1, flags: S Incoming interface: GigabitEthernet0/0, RPF nbr 10.0.0.1 Outgoing interface list: GigabitEthernet0/1, Forward/Sparse, 00:03:45/00:02:15 Based on this output, what can be concluded?

A.The group is using PIM dense mode.
B.The RP for this group is 10.0.0.1.
C.The multicast traffic is being hardware switched.
D.The group is a Bidir group.
AnswerB

The output clearly states 'RP 10.0.0.1' in the (*,G) entry.

Why this answer

The 'show ip mroute' output shows a (*,G) entry for group 239.1.1.1 with flags 'S' (Sparse mode) and an RP of 10.0.0.1. The incoming interface is GigabitEthernet0/0 with RPF neighbor 10.0.0.1, and the outgoing interface list includes GigabitEthernet0/1 in Forward state. This indicates that the multicast route is using PIM sparse mode and the RP is known.

The correct answer is that PIM sparse mode is used with an RP at 10.0.0.1.

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33
MCQmedium

What is the default multicast group range for Source-Specific Multicast (SSM) as defined by IANA and supported by Cisco IOS?

A.224.0.0.0/4
B.232.0.0.0/8
C.239.0.0.0/8
D.233.0.0.0/8
AnswerB

Correct. 232.0.0.0/8 is the default SSM range.

Why this answer

The IANA has reserved the 232.0.0.0/8 address range for SSM. Cisco IOS uses this range by default for SSM, and it can be modified with the 'ip pim ssm' command.

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34
Drag & Dropmedium

Drag and drop the steps of RPF check verification for multicast forwarding into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

The RPF check ensures that incoming multicast packets arrive on the correct interface toward the source. First, the router examines the source IP address. Then it consults the unicast routing table to find the best route.

It identifies the outgoing interface for that route. It compares that interface with the arrival interface of the multicast packet. If they match, the packet is forwarded; otherwise, it is dropped.

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35
Matchingmedium

Drag and drop each multicast address range on the left to its matching use on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Link-local multicast (e.g., OSPF, EIGRP, PIM hello)

Source-Specific Multicast (SSM) range

Administratively scoped (private) multicast

Global unicast-based multicast (GLOP, SSM not included)

Entire IPv4 multicast address space

Why these pairings

224.0.0.0/24 is reserved for link-local multicast (e.g., routing protocols); 232.0.0.0/8 is for SSM; 239.0.0.0/8 is for administratively scoped (private) multicast; 224.0.1.0–238.255.255.255 is for global unicast-based multicast; 224.0.0.0/4 is the overall multicast range.

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36
Multi-Selectmedium

Which two statements about PIM sparse mode (PIM-SM) are true? (Choose two.)

Select 2 answers
A.PIM-SM uses a pull model where receivers explicitly join the multicast group.
B.In PIM-SM, the rendezvous point (RP) is the root of the shared tree.
C.PIM-SM automatically switches to the shortest path tree (SPT) immediately after the first multicast packet is received.
D.PIM-SM requires all routers in the domain to be configured with the same RP address.
E.PIM-SM supports only one RP per multicast group.
AnswersA, B

Correct because PIM-SM requires receivers to send IGMP joins, which trigger PIM joins toward the RP, pulling traffic only where needed.

Why this answer

PIM-SM uses a pull model where receivers join the shared tree via the RP, and the RP is the root of the shared tree. The SPT switchover occurs after the first packet arrives via the shared tree.

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37
Matchingmedium

Drag and drop each IGMP version on the left to its matching feature on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

No leave message; querier elected by lowest IP address on subnet

Supports explicit leave message and querier election using lowest IP address

Supports source-specific group membership (include/exclude lists) and SSM

Why these pairings

IGMPv1 has no leave message and uses a querier election based on IP address; IGMPv2 adds explicit leave and querier election using lowest IP; IGMPv3 adds source filtering (include/exclude) and supports SSM.

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38
MCQmedium

A network engineer runs the following command on Router R1: R1# show ip pim neighbor PIM Neighbor Table Neighbor Address Interface Uptime Expires Mode 10.1.1.2 GigabitEthernet0/0 2w0d 00:01:25 DR 10.1.1.3 GigabitEthernet0/0 2w0d 00:01:20 B Based on this output, what can be concluded?

A.PIM sparse mode is operating on this interface.
B.PIM Bidir mode is configured on this interface.
C.PIM dense mode is in use on this interface.
D.PIM SSM is enabled on this interface.
AnswerB

The B flag in the Mode column indicates Bidir capability, and the DR flag is also present, which is consistent with Bidir operation.

Why this answer

The 'show ip pim neighbor' output shows two neighbors on the same interface. The 'Mode' column indicates the PIM neighbor role: 'DR' means Designated Router, 'B' means Bidir-capable. The presence of both DR and B on the same interface suggests that PIM Bidir mode is enabled, as Bidir uses a different DR election and the B flag indicates Bidir capability.

The correct answer is that PIM Bidir is configured.

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39
MCQmedium

A network engineer runs the following command on Router R6: R6# show ip pim rp 239.3.3.3 RP 10.0.0.4 Info source: 10.0.0.4, via bootstrap, priority 192, holdtime 150, expires in 00:02:30 Based on this output, what can be concluded?

A.The RP was learned via Auto-RP.
B.The RP was learned via BSR.
C.The RP was statically configured.
D.The RP is 10.0.0.5.
AnswerB

The output explicitly states 'via bootstrap'.

Why this answer

The 'show ip pim rp' command shows the RP for group 239.3.3.3 is 10.0.0.4, learned via bootstrap (BSR). The priority is 192, holdtime 150 seconds, and it expires in 2 minutes 30 seconds. This indicates that BSR is the mechanism used to learn the RP.

The correct answer is that the RP was learned via BSR.

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40
MCQmedium

Consider the following configuration snippet on a Cisco IOS-XE router: interface GigabitEthernet0/1 ip address 10.1.1.1 255.255.255.0 ip pim sparse-mode ip igmp version 3 ! router ospf 1 network 10.1.1.0 0.0.0.255 area 0 ! What is the effect of this configuration?

A.The interface will participate in PIM sparse-mode and IGMPv3, but PIM sparse-mode requires an RP to be configured or learned.
B.The interface will operate in PIM dense-mode because no RP is configured.
C.IGMPv3 is incompatible with PIM sparse-mode and will be ignored.
D.The router will automatically use dense-mode because OSPF is enabled.
AnswerA

Correct. PIM sparse-mode requires an RP. IGMPv3 is supported but the RP must be defined for sparse-mode to work.

Why this answer

The interface is configured with PIM sparse-mode and IGMPv3. PIM sparse-mode requires a rendezvous point (RP) to be known, either statically or via Auto-RP/BSR. IGMPv3 allows source-specific multicast (SSM) with the SSM range (232.0.0.0/8).

OSPF is enabled on the interface for unicast routing. The configuration is valid but missing an RP definition for sparse-mode to function correctly.

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41
Drag & Dropmedium

Drag and drop the steps of multicast RP discovery using Auto-RP into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

Auto-RP uses a mapping agent that listens for RP announcements, then advertises the RP mapping via a well-known group; all routers learn the RP and use it for group-to-RP mapping.

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42
Multi-Selectmedium

Which two statements about IGMP snooping are true? (Choose two.)

Select 2 answers
A.IGMP snooping reduces unnecessary multicast flooding on a Layer 2 switch.
B.IGMP snooping uses the IGMP querier election process to select the switch with the highest IP address as the querier.
C.IGMP snooping can be configured to replace IGMP on the router interface.
D.IGMP snooping listens to IGMP membership reports and leave messages to build a forwarding table.
E.IGMP snooping modifies the IP header of multicast packets to include group membership information.
AnswersA, D

Correct because IGMP snooping allows the switch to forward multicast frames only to ports that have joined the group, reducing flooding.

Why this answer

IGMP snooping operates on Layer 2 switches to constrain multicast traffic to only those ports that have interested receivers. It listens to IGMP messages between hosts and routers to build a forwarding table. It does not replace IGMP; it is complementary.

The querier is elected based on the lowest IP address, not the highest. IGMP snooping does not modify IP multicast headers.

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43
MCQmedium

Given the following configuration on a Cisco IOS-XE router: ip multicast-routing ! interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip pim sparse-mode ip igmp version 2 ! router ospf 1 network 10.1.1.0 0.0.0.255 area 0 ! What is missing from this configuration to support Source-Specific Multicast (SSM) for group range 232.0.0.0/8?

A.The interface must be configured with 'ip igmp version 3' to support SSM.
B.The router must be configured with 'ip pim ssm' command to enable SSM.
C.An RP must be configured for the 232.0.0.0/8 range.
D.The interface must be configured with 'ip pim dense-mode' for SSM to work.
AnswerA

Correct. IGMPv3 is required for SSM to allow hosts to specify sources in their membership reports.

Why this answer

SSM requires IGMPv3 to allow hosts to specify sources. The configuration uses IGMPv2, which does not support source filtering. Additionally, PIM sparse-mode is used, but SSM typically uses PIM SSM (which is essentially PIM sparse-mode with the SSM range).

The missing piece is IGMPv3; the SSM range is automatically enabled for 232.0.0.0/8 when IGMPv3 is configured.

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44
MCQmedium

An engineer is troubleshooting multicast performance issues. The network uses PIM sparse mode with a static RP. The engineer notices that the multicast traffic from a source to a group is taking a suboptimal path, causing high latency. The engineer checks the multicast routing table on the last-hop router and sees that the (S,G) entry has an incoming interface that is not the shortest path to the source. What is the most likely reason for this suboptimal path?

A.The last-hop router has not yet switched to the SPT.
B.The RP is not configured as the DR on its segment.
C.The multicast source is using a different group address.
D.The last-hop router has a higher metric to the source than to the RP.
AnswerA

Correct because the default behavior is to switch to the SPT after the first packet, but if disabled or delayed, the shared tree is used.

Why this answer

In PIM sparse mode, the last-hop router initially joins the shared tree toward the RP. After receiving the first packet, it can optionally switch to the shortest path tree (SPT) by sending a join toward the source. If the SPT switchover is disabled or delayed, the traffic continues to use the shared tree, which may be suboptimal.

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45
Matchingmedium

Drag and drop each PIM mode on the left to its matching traffic distribution method on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Uses explicit join messages to build a shared tree

Floods multicast traffic on all interfaces, then prunes unwanted branches

Builds shortest path trees from source to receivers

Uses a shared tree with no source-specific state

Operates in sparse mode by default, but allows dense mode per group

Why these pairings

PIM Sparse Mode uses explicit join to build a shared tree; Dense Mode floods initially then prunes; Source-Specific Mode uses shortest path trees from source; Bidirectional PIM uses a shared tree with no source-specific state.

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46
MCQeasy

What is the default IGMP version on a Cisco IOS interface when IP multicast routing is enabled?

A.IGMPv1
B.IGMPv2
C.IGMPv3
D.IGMPv2 is default only if PIM is enabled; otherwise, no IGMP.
AnswerB

Correct. IGMPv2 is the default on Cisco IOS interfaces.

Why this answer

The default IGMP version on Cisco IOS interfaces is version 2, which is widely supported and provides basic membership reporting and querying.

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47
Drag & Dropmedium

Drag and drop the steps of IGMPv3 membership report processing into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

IGMPv3 allows hosts to specify source filtering. The host sends a Membership Report with group and source list. The switch/router receives the report and updates its multicast forwarding table.

It adds the group and includes the requested sources. It then forwards multicast traffic from those sources to the host's port. The router periodically sends General Queries to maintain membership.

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48
Drag & Dropmedium

Drag and drop the steps of MSDP peering for inter-domain multicast into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

MSDP allows RPs in different domains to share information about active sources. When an RP learns of a new source, it sends a Source-Active (SA) message to its MSDP peers. The peer RP then creates an (S,G) state and can join the source if there are interested receivers.

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49
Drag & Dropmedium

Drag and drop the steps of PIM-SM join and source registration into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

In PIM-SM, a receiver's DR sends a (*,G) Join toward the RP. The RP then sends a (S,G) Join toward the source. The source's DR registers the source with the RP via a unicast Register message.

The RP de-encapsulates the Register and sends a Register-Stop back to the source's DR to stop the registration process.

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50
Matchingmedium

Drag and drop each IGMP version on the left to its matching feature on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Uses a query/response model with no leave group message

Adds leave group messages and querier election

Adds source filtering (include/exclude lists)

Why these pairings

IGMPv1 uses a query/response model; IGMPv2 adds leave group messages and querier election; IGMPv3 adds source filtering (include/exclude).

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51
Drag & Dropmedium

Drag and drop the steps of PIM DM (Dense Mode) flood and prune steps into the correct order, from first to last.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps
Order
1Step 1
2Step 2
3Step 3
4Step 4
5Step 5

Why this order

PIM DM initially floods multicast traffic to all PIM-enabled interfaces; downstream routers that have no interested receivers send Prune messages upstream to stop unwanted traffic.

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52
MCQmedium

Consider the following configuration on a Cisco IOS-XE router: ip multicast-routing ! interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 ip pim sparse-mode ip igmp static-group 239.1.1.1 ! What is the effect of the 'ip igmp static-group 239.1.1.1' command?

A.The router will send IGMP membership reports for group 239.1.1.1 out of this interface.
B.The router will include this interface in the outgoing interface list for group 239.1.1.1, even without any IGMP hosts.
C.The router will drop all multicast traffic for group 239.1.1.1 on this interface.
D.The router will create a static multicast route for 239.1.1.1 via this interface.
AnswerB

Correct. The static-group command adds the interface to the OIL (outgoing interface list) for the group, simulating a receiver.

Why this answer

The 'ip igmp static-group' command statically adds the interface to the multicast group 239.1.1.1, meaning the router will treat the interface as if a host has joined that group. This can be used for testing or to ensure multicast traffic is forwarded to that interface even without an active IGMP member.

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53
Matchingmedium

Drag and drop each PIM message type on the left to its matching function on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Discovers PIM neighbors and maintains adjacency

Requests to receive multicast traffic for a specific group (or S,G)

Requests to stop receiving multicast traffic for a specific group (or S,G)

Resolves which PIM router forwards multicast traffic on a multi-access network

Distributes RP information in PIM Sparse Mode

Why these pairings

PIM Hello discovers neighbors and maintains adjacency; Join is used to join a multicast tree; Prune is used to leave a tree; Assert resolves duplicate forwarding on a multi-access network; Bootstrap messages are used in PIM SM to distribute RP information.

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54
MCQhard

A network engineer issues the following command on Router R7: R7# show ip pim tunnel Tunnel1: Type: PIM Encap Source: 10.0.0.7, Destination: 10.0.0.8 Status: up Based on this output, what can be concluded?

A.This tunnel is used for PIM register encapsulation to the RP.
B.This tunnel is used for MDT data group forwarding.
C.This tunnel is used for BSR messages.
D.This tunnel is used for Auto-RP announcements.
AnswerA

PIM Encap tunnels are used to encapsulate multicast packets from the first-hop router to the RP.

Why this answer

The 'show ip pim tunnel' output shows a PIM encapsulation tunnel (Tunnel1) with source 10.0.0.7 and destination 10.0.0.8, and the status is up. This type of tunnel is used for PIM register encapsulation when a source sends to an RP. The correct answer is that this tunnel is used for sending register messages to the RP.

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55
Matchingmedium

Drag and drop each multicast address range on the left to its matching use on the right.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts
Matches

Reserved for link-local multicast (e.g., routing protocols)

Used for Source-Specific Multicast (SSM)

Administratively scoped (private) multicast

All hosts on this subnet (link-local all-hosts group)

All routers on this subnet (link-local all-routers group)

Why these pairings

224.0.0.0/24 is reserved for link-local multicast; 232.0.0.0/8 is for Source-Specific Multicast; 239.0.0.0/8 is for administratively scoped (private) multicast.

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56
MCQmedium

Given the following partial configuration on a Cisco IOS-XE router: ip pim rp-address 10.0.0.1 10 access-list 10 permit 224.0.0.0 0.255.255.255 ! interface GigabitEthernet0/0 ip pim sparse-mode ! What is the effect of this configuration?

A.The router will use 10.0.0.1 as the RP for all multicast groups from 224.0.0.0 to 224.255.255.255, and the interface will operate in sparse-mode.
B.The router will ignore the static RP because the ACL includes the reserved link-local range (224.0.0.0/24).
C.The interface must also be configured with 'ip pim dense-mode' for the RP to work.
D.The RP address 10.0.0.1 must be configured on a loopback interface on the same router.
AnswerA

Correct. The static RP is defined for the group range specified in ACL 10, and the interface is in sparse-mode.

Why this answer

This configures a static RP at 10.0.0.1 for multicast groups matching access-list 10, which permits all groups in the 224.0.0.0/8 range. The interface is in PIM sparse-mode. However, the RP address must be reachable via unicast routing.

The configuration is valid but note that 224.0.0.0/8 includes reserved link-local addresses (224.0.0.0/24) which are not typically used with PIM.

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57
Multi-Selecthard

Which three statements about RPF check in IP multicast are true? (Choose three.)

Select 3 answers
A.The RPF check ensures that multicast packets are forwarded only if they arrive on the interface that the router would use to send unicast traffic back to the source.
B.If the RPF check fails, the multicast packet is dropped by the router.
C.The RPF check is performed only on the first packet of a multicast stream to determine the forwarding path.
D.The RPF check relies solely on the multicast routing table (MRIB) to determine the incoming interface.
E.A multicast packet can fail the RPF check even if the unicast route to the source exists, if the packet arrives on a different interface than the one used for unicast return traffic.
AnswersA, B, E

Correct because the RPF check uses the unicast routing table to determine the expected incoming interface for the source.

Why this answer

The RPF check is a fundamental multicast forwarding mechanism that verifies the source address of incoming multicast packets against the unicast routing table. A packet passes RPF if it arrives on the interface that the router would use to reach the source. If the RPF check fails, the packet is dropped to prevent loops.

RPF is performed on every multicast packet, not just the first one. The RPF check is independent of the multicast routing protocol; it uses the unicast routing table. RPF failure can occur even with a correct unicast route if the packet arrives on a different interface.

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58
Multi-Selectmedium

Which three statements about IGMP snooping are true? (Choose three.)

Select 3 answers
A.IGMP snooping reduces multicast flooding on a VLAN by forwarding traffic only to ports that have joined the group.
B.IGMP snooping builds a Layer 2 forwarding table that maps multicast MAC addresses to switch ports.
C.IGMP snooping forwards IGMP membership reports only toward the multicast router (querier).
D.IGMP snooping suppresses all IGMP general queries from the multicast router.
E.IGMP snooping requires PIM to be enabled on the switch.
AnswersA, B, C

Correct because IGMP snooping examines IGMP join messages and builds a forwarding table so multicast frames are sent only to interested receivers.

Why this answer

IGMP snooping optimizes multicast forwarding at Layer 2 by monitoring IGMP messages. It builds a snooping table, forwards reports only to the querier, and can be configured with static entries. It does not suppress queries or require PIM.

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