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CCNA IP Multicast Questions

37 questions · IP Multicast · All types, answers revealed

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1
MCQmedium

An ISP engineer is troubleshooting an interdomain multicast deployment. A receiver in AS 65001 wants to receive a stream sourced in AS 65002. The RP in AS 65001 has no (S,G) state for the source, and the RP in AS 65002 is not sending any Source-Active messages. Both RPs are configured as MSDP peers over a working TCP session. Which statement explains why the RP in AS 65001 lacks source information?

A.The RP in AS 65001 must be configured as a candidate RP for the source's group range to receive Source-Active messages.
B.The RP in AS 65002 must receive a PIM Register from the source's first-hop router before it can originate Source-Active messages.
C.The MSDP TCP session must be encrypted with IPsec before Source-Active messages are exchanged.
D.The receiver's last-hop router must send an MSDP Source-Active request to the remote RP before any messages are sent.
AnswerB

An RP only knows about a source after the source's first-hop router sends a PIM Register to it. Once the RP has (S,G) state, it generates Source-Active messages toward its MSDP peers. If no Register arrives, the RP has no source to advertise, so the peer RP in the other domain receives nothing and cannot build interdomain state for the receiver.

Why this answer

Interdomain multicast with MSDP depends on the source domain's RP learning about active sources. The first-hop router registers sources with its local RP using PIM Register messages. Only after the RP has (S,G) state does it originate Source-Active messages to its MSDP peers.

If no Register reaches that RP, no SA messages are generated, and the peer RP in the receiving domain has nothing to install.

Exam trap

The trap here is focusing on the MSDP TCP session state while overlooking that the source-side RP must first learn the source through PIM registration.

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2
MCQmedium

You administer a Junos router that has two equal-cost paths toward the PIM rendezvous point for group 239.1.1.1. Users report intermittent multicast outages whenever the unicast route to the RP flaps. You want to eliminate the dependency on unicast reachability to the RP for this group. Which configuration accomplishes this?

A.Configure a static RP for the group with the address of the local router's loopback interface.
B.Configure the group in a PIM source-specific multicast (SSM) group range on all routers in the path.
C.Configure the group as a PIM sparse-dense-mode group so it uses source-specific trees.
D.Enable PIM dense-mode on the interfaces facing the multicast receivers for the group.
AnswerB

SSM groups do not use a rendezvous point or a shared tree; receivers join the (S,G) channel directly, typically via IGMPv3, and PIM builds only the shortest-path tree. Because no RP is consulted, the flapping unicast route to the RP no longer affects delivery for this group, which is exactly what the scenario requires.

Why this answer

Source-specific multicast removes the rendezvous point from the forwarding path for the configured group range. Receivers signal interest in a specific source and group, and PIM immediately builds a shortest-path tree toward that source without any shared-tree or RP interaction. Because the RP address is never resolved, a flapping unicast route toward the RP cannot disrupt delivery for that group.

Exam trap

The trap here is assuming that changing how the RP is discovered, such as using a static or anycast RP, removes the RP dependency, when only moving the group into an SSM range eliminates the RP from the tree entirely.

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3
MCQeasy

Which operational command is used to verify the operational status and peer state of MSDP sessions on a Junos device?

A.show igmp summary
B.show msdp summary
C.show pim summary
D.show multicast summary
AnswerB

`show msdp summary` lists each MSDP peer with its state and session counts, directly satisfying the requirement to verify peer state. Unlike `show msdp statistics`, which reports message counters, or `show msdp source-active`, which displays cached source information, this command exposes the operational peer relationship itself.

Why this answer

The 'show msdp summary' command provides an overview of MSDP peers, state, and connection status.

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4
Multi-Selectmedium

Which TWO statements describe the function and operation of a PIM Bootstrap Router (BSR)? (Choose two)

Select 2 answers
A.The BSR acts as the data encapsulation point for multicast sources.
B.The BSR collects Candidate-RP messages and periodically distributes the RP-set to all PIM routers.
C.The BSR forwards multicast data packets directly to receivers.
D.All PIM routers in the domain dynamically learn the RP-set from the BSR messages.
E.The BSR is required to establish MSDP sessions between autonomous systems.
AnswersB, D

The BSR gathers Candidate-RP advertisements and floods the resulting RP-set to every PIM router in the domain, enabling group-to-RP mapping without static configuration. This satisfies the dynamic RP discovery requirement, since routers learn which RPs serve which multicast groups.

Why this answer

The BSR collects Candidate-RP advertisements and distributes the RP-set to all routers in the domain via bootstrap messages.

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5
MCQmedium

An administrator wants to configure Candidate-RP (C-RP) advertisements using the Bootstrap Router (BSR) mechanism in PIM sparse-mode. Which hierarchy level in Junos is used to configure the local router as a Candidate-RP?

A.[edit protocols pim bsr]
B.[edit routing-options candidate-rp]
C.[edit protocols pim candidate-rp]
D.[edit protocols igmp candidate-rp]
AnswerC

Junos configures the local router as a Candidate-RP under the [edit protocols pim candidate-rp] hierarchy level, where the RP address, priority and group ranges are defined for BSR advertisement. The BSR mechanism then propagates this candidacy to other PIM routers.

Why this answer

Candidate RPs in Junos are configured under protocols pim candidate-rp.

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6
MCQeasy

An administrator is enabling PIM sparse-mode on a Junos router that connects to a Layer 2 switch carrying several user VLANs. Receivers on those VLANs need to join multicast groups, but the router is not seeing any IGMP membership reports from the hosts. PIM is enabled on the router's interface toward the switch. Which action is required on the router to receive IGMP reports?

A.Enable IGMP on the interface facing the VLANs in addition to PIM sparse-mode.
B.Enable PIM dense-mode on the interface so IGMP reports are flooded to all routers.
C.Enable IGMP snooping on the router interface facing the VLANs.
D.Configure a static IGMP group join for each multicast group on the router interface.
AnswerA

PIM sparse-mode handles multicast routing between routers, but it does not process host IGMP membership reports. To learn about receivers on directly attached subnets, the router interface must have IGMP enabled for the appropriate version. Without IGMP on that interface, the router never builds the local membership state needed to trigger a PIM join toward the RP.

Why this answer

PIM sparse-mode operates between multicast routers and does not itself interpret host IGMP membership reports. For a router to learn that receivers on a directly attached subnet want a group, IGMP must be enabled on that interface. The resulting local membership state causes the router to send a PIM join toward the RP.

IGMP snooping belongs on the switch, and static joins bypass rather than enable dynamic membership.

Exam trap

The trap here is assuming that enabling PIM sparse-mode on an interface automatically enables IGMP processing for hosts on that subnet.

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7
Multi-Selectmedium

An engineer is configuring PIM sparse-mode in an enterprise network. Which TWO characteristics are true regarding PIM sparse-mode operation? (Choose two)

Select 2 answers
A.It requires every interface to run IGMPv3 exclusively.
B.It floods multicast traffic across all router interfaces by default until pruned.
C.It uses explicit join messages (*,G or S,G) sent towards the RP or source.
D.It does not require any unicast routing protocol for RPF checks.
E.It relies on a Rendezvous Point (RP) to bridge sources and receivers during tree establishment.
AnswersC, E

Sparse-mode builds distribution trees on demand: receivers send explicit PIM Join messages, either (*,G) towards the RP or (S,G) towards the source, and traffic only flows where joins exist. This pull-model join behaviour is fundamental to sparse-mode operation.

Why this answer

Option C is correct because PIM-SM is an explicit-join protocol: receivers' DRs send (*,G) joins toward the Rendezvous Point and, after the shortest-path tree switchover, (S,G) joins toward the source, building distribution trees only where membership exists. Option E is correct because PIM-SM uses a shared tree rooted at the RP to connect sources and receivers initially, with the RP forwarding traffic until routers can join the source-specific shortest-path tree. Option A is wrong because PIM-SM does not mandate IGMPv3 on every interface; IGMPv2 or IGMPv3 may be used, and IGMP is only relevant on receiver-facing segments.

Option B is wrong because flooding-until-pruned behavior describes PIM dense mode, not sparse mode. Option D is wrong because PIM-SM relies on the unicast routing table (or MRIB) for RPF checks to prevent loops and select the correct upstream neighbor.

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8
MCQeasy

An engineer needs to verify which multicast groups have active receivers joined on an interface using IGMP. Which operational command should be used?

A.show igmp group
B.show multicast heap
C.show msdp SA-cache
D.show pim rp statistics
AnswerA

`show igmp group` lists every multicast group with joined receivers, displaying the interface each membership was learned on. This directly satisfies the requirement to verify which groups have active receivers joined on an interface, since the output includes group address, interface, and membership state per entry.

Why this answer

The 'show igmp group' command lists the multicast groups joined on interfaces via IGMP.

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9
MCQhard

An enterprise design requires configuring an Anycast RP setup using two Junos routers to provide redundancy for PIM sparse-mode. Which mechanism is required to synchronize source state information between the two Anycast RPs within the same AS?

A.Multicast Source Discovery Protocol (MSDP)
B.Protocol Independent Multicast Dense-Mode (PIM-DM)
C.IGMPv3 snooping
D.Multicast BGP (MBGP)
AnswerA

MSDP is used between Anycast RPs to exchange source-active information so that receivers joined to one RP learn about sources registered to the other RP.

Why this answer

When deploying Anycast RP within a single PIM domain using MSDP, MSDP peer connections are established between the Anycast RP addresses to exchange SA (Source Active) messages, ensuring both RPs know about sources registered to either RP.

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10
MCQmedium

An enterprise network runs PIM sparse-mode with a static RP. A Junos router receives a PIM Register message from a directly connected first-hop router for a new multicast source. The router is the RP for that group. Which action does the RP take upon receiving the Register message?

A.It immediately sends a Register-Stop to the first-hop router and waits for the source to send native multicast traffic.
B.It forwards the Register message to the BSR to request a new RP mapping for the group.
C.It sends a PIM Join toward the source to build the shortest-path tree and then sends a Register-Stop to the first-hop router.
D.It immediately decapsulates the Register message and forwards the multicast data to the shared tree.
AnswerC

The RP first sends a PIM Join toward the source, building (S,G) state. Once the source tree is established and the RP starts receiving native multicast traffic, it sends a Register-Stop to the first-hop router. This transitions the source from the register encapsulation to native forwarding along the shortest-path tree, which is the correct PIM-SM behavior.

Why this answer

When a first-hop router receives multicast traffic from a new source, it encapsulates the data in PIM Register messages and unicasts them to the RP. The RP, upon receiving the Register, must join the source tree by sending a PIM Join toward the source. Once the RP starts receiving native multicast traffic on the source tree, it sends a Register-Stop to the first-hop router to stop the encapsulation.

This ensures efficient forwarding along the shortest-path tree.

Exam trap

The trap here is assuming the RP immediately sends a Register-Stop or decapsulates without first building the source tree, which would cause traffic disruption.

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11
MCQeasy

A network administrator needs to display the multicast routing table entries, including incoming interfaces and outgoing interface lists (OIL), on a Junos device. Which operational command should be used?

A.show ospf route
B.show multicast route
C.show igmp interface
D.show pim join
AnswerB

The show multicast route command displays the multicast forwarding table, listing each (S,G) or (*,G) entry with its incoming interface and outgoing interface list. This directly satisfies the requirement to view OIL entries, unlike show route, which covers unicast routing only.

Why this answer

The 'show multicast route' command displays the Multicast Forwarding Information Base (MFIB) entries, including source, group, incoming interface, and outgoing interfaces.

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12
MCQeasy

An administrator is configuring a Junos device to support IGMPv3 on user-facing VLAN interfaces. Which configuration statement enables IGMPv3 processing on interface irb.10?

A.set protocols pim interface irb.10 igmp-version 3
B.set interfaces irb.10 family inet igmp-version v3
C.set protocols igmp interface irb.10 version 3
D.set routing-options multicast igmp-version 3
AnswerC

`set protocols igmp interface irb.10 version 3` explicitly sets the IGMP version to 3 on the IRB interface, satisfying the requirement to enable IGMPv3 processing on user-facing VLAN interfaces. Junos defaults to IGMPv2, so the version statement is mandatory to activate v3 source-specific multicast behaviour on irb.10.

Why this answer

IGMP version selection on Junos interfaces is configured under protocols igmp interface.

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13
Multi-Selecthard

An administrator is troubleshooting an MSDP deployment between two autonomous systems. Which THREE factors can cause an MSDP peer session to fail to establish? (Choose three)

Select 3 answers
A.TCP port 639 being blocked by a firewall between the peers
B.Incorrect local source IP address specified in the MSDP peer configuration
C.A mismatch in configured MD5 authentication passwords between the peers
D.An incorrect IGMPv2 timer setting on the receiver VLAN
E.An invalid PIM dense-mode setting on the core interface
AnswersA, B, C

MSDP relies on TCP connections over port 639, so blocking this port prevents session establishment.

Why this answer

MSDP runs over TCP port 639. Session establishment requires correct peer IP configuration, functional TCP connectivity, and matching authentication keys if configured.

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14
MCQhard

A Junos router is the last-hop router for receivers in VLAN 100. The receivers use IGMPv3 and request group 239.5.5.5 from source 10.10.10.10 only. The router has a PIM sparse-mode shared tree (*,G) toward the RP, but traffic from 10.10.10.10 is not being delivered to the receivers. The unicast route to 10.10.10.10 points out a different interface than the one toward the RP. Which action resolves the problem?

A.Add a static IGMP group membership for 239.5.5.5 on the VLAN 100 interface.
B.Configure an RP for the group so the shared tree can be used for delivery.
C.Increase the IGMP query interval on VLAN 100 so the receiver reports are refreshed more often.
D.Ensure PIM is enabled on the interface toward 10.10.10.10 so the router can build the (S,G) tree.
AnswerD

A source-specific join must follow the unicast route to the source, which points out a different interface than the RP path. PIM must be enabled on that outgoing interface for the router to send the (S,G) join and receive the source traffic. Without PIM on that interface, the source tree cannot be built, so enabling it resolves the delivery failure.

Why this answer

When a receiver requests a specific source and group, the last-hop router must create (S,G) state and send a PIM join toward the source using the unicast route to the source address. That route can differ from the path toward the rendezvous point. If PIM is not enabled on the outgoing interface toward the source, the join cannot be sent and traffic is never forwarded, so PIM must be enabled on that interface.

Exam trap

The trap here is assuming that the shared tree toward the rendezvous point is sufficient for a source-specific request, when the source path may follow a completely different interface that also requires PIM to be enabled.

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15
MCQmedium

An engineer needs to verify the Rendezvous Point (RP) currently learned via the Bootstrap Router (BSR) mechanism on a Junos device. Which operational command should be used?

A.show pim rps
B.show igmp rp
C.show msdp rp-list
D.show multicast rp-table
AnswerA

`show pim rps` displays the RP set that PIM has learned, including entries sourced via BSR, with their group ranges, priority and holdtime. It directly satisfies the stem's requirement to verify the currently learned BSR RP on the Junos device, unlike commands showing interface or neighbour state.

Why this answer

The 'show pim rps' command displays all active RPs known to the router, including whether they were learned via static configuration, Auto-RP, or BSR.

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16
MCQeasy

A Junos router connects to a Layer 2 switch that has multiple receivers on VLAN 200. The switch is not running PIM, and the router is the only multicast router on the segment. You want the router to send IGMP general queries on the VLAN 200 interface and track receiver group memberships. Which configuration is required?

A.Configure a static multicast route for 224.0.0.0/4 pointing out the VLAN 200 interface.
B.Enable IGMP on the VLAN 200 interface with a version compatible with the receivers.
C.Enable PIM sparse-mode on the VLAN 200 interface and configure an RP.
D.Enable IGMP snooping on the router's VLAN 200 interface.
AnswerB

IGMP must be enabled on the interface facing the receivers so the router can send general queries and process membership reports. The version must match the receivers, since IGMPv2 and IGMPv3 report formats differ and mismatch causes memberships to be ignored. This directly satisfies the requirement to query and track memberships on VLAN 200.

Why this answer

The router must run IGMP on the interface that faces the receivers to act as the querier and maintain group membership state. IGMP queries solicit reports, and the reports populate the membership database that drives PIM joins. PIM alone does not perform this signaling, and IGMP snooping is a switch-side optimization, so IGMP on the interface with a matching version is the required configuration.

Exam trap

The trap here is confusing IGMP snooping, a Layer 2 switch optimization, with IGMP itself, which a router must run on the receiver-facing interface to query and track memberships.

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17
Multi-Selectmedium

An administrator is configuring IGMP snooping on an EX Series switch. Which TWO benefits does IGMP snooping provide in a switched Ethernet environment? (Choose two)

Select 2 answers
A.It automatically acts as the PIM Rendezvous Point for the VLAN.
B.It conserves bandwidth on switch links by filtering unwanted multicast streams.
C.It translates IPv4 multicast addresses to IPv6 multicast addresses.
D.It replaces PIM sparse-mode on Layer 3 core routers.
E.It prevents multicast traffic from flooding all ports in a VLAN by forwarding it only to ports with active receivers.
AnswersB, E

Snooping builds a per-VLAN group membership table from IGMP reports, so multicast is forwarded only to interested ports rather than every port. That filtering of unwanted streams conserves bandwidth on switch links, satisfying the stated benefit.

Why this answer

Option B is correct because IGMP snooping lets the switch listen to IGMP Membership Reports and Leave messages, so it can prune multicast streams from switch links where no receivers exist, thereby conserving bandwidth on those links. Option E is correct because, by default, a Layer 2 switch floods multicast frames out every port in the VLAN; IGMP snooping builds a per-VLAN multicast forwarding table and forwards each group's traffic only to ports that have joined that group via IGMP, preventing unnecessary flooding. Option A is wrong because the PIM Rendezvous Point is a Layer 3 multicast routing function, not something IGMP snooping provides on a switch.

Option C is wrong because IGMP snooping does not perform any IPv4-to-IPv6 multicast address translation. Option D is wrong because IGMP snooping operates at Layer 2 and does not replace PIM sparse-mode, which is required for multicast routing between subnets on Layer 3 devices.

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18
MCQeasy

A network administrator is configuring an enterprise router to join the Source-Specific Multicast (SSM) range. According to RFC standards, what is the standard IPv4 address block reserved for SSM?

A.239.0.0.0/8
B.232.0.0.0/8
C.224.0.0.0/24
D.224.0.1.0/24
AnswerB

232.0.0.0/8 is the IPv4 block RFC 4607 reserves for Source-Specific Multicast, satisfying the stem's requirement for the standard SSM range. SSM delivers traffic only from explicitly requested sources, so receivers use IGMPv3 or MLDv2 to specify both group and source, unlike ASM's shared 224.0.0.0/4 space.

Why this answer

The range 232.0.0.0/8 is globally reserved by IANA for Source-Specific Multicast (SSM).

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19
MCQhard

An engineer is deploying PIM sparse-mode with anycast RP using two Junos routers that share the loopback address 10.0.0.1/32. Both routers are configured as static RPs for all groups and as MSDP peers with each other using their unique loopback addresses. Receivers attached to Router A join a group whose source is registered with Router B. Traffic initially flows, but after Router B reloads, receivers lose the stream even though Router A still has the anycast RP address reachable. Which mechanism is responsible for restoring source information to Router A?

A.Router A learns the source through the shared (*,G) tree because both routers use the same anycast RP address.
B.The first-hop router sends a PIM Assert to Router A to advertise the source location after the reload.
C.Router B re-registers the source with Router A through PIM Register messages sent to the anycast address.
D.Router B sends Source-Active messages to Router A over the MSDP peering once it relearns the source from the first-hop router.
AnswerD

In anycast RP, MSDP peering between the RP instances synchronizes active source information. After Router B reloads, the source's first-hop router re-registers with B, which rebuilds (S,G) state and sends Source-Active messages to its MSDP peer Router A. Router A can then join toward the source, restoring delivery to receivers attached to it.

Why this answer

Anycast RP uses a shared RP address on multiple routers plus MSDP peering between them using unique addresses. When one RP instance relearns a source through PIM registration, it advertises that source to its MSDP peers with Source-Active messages. The other RP instance installs the state and can build a path for its receivers.

Without MSDP synchronization, receivers attached to the instance that lacks (S,G) state would remain without the stream.

Exam trap

The trap here is expecting the shared anycast RP address alone to synchronize source state, when MSDP peering is what actually exchanges active source information.

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20
MCQmedium

An engineer wants to configure a Junos router to act as a Bootstrap Router (BSR) for PIM sparse-mode. Which configuration hierarchy is used to enable the BSR function?

A.[edit protocols msdp bsr]
B.[edit protocols pim bsr]
C.[edit routing-options bsr]
D.[edit protocols pim candidate-rp]
AnswerB

BSR operation is enabled under the [edit protocols pim bsr] hierarchy, where the local router is configured as candidate BSR with priority and as candidate rendezvous point. This satisfies the requirement for PIM sparse-mode bootstrap election.

Why this answer

BSR functionality on Junos is configured under protocols pim bsr.

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21
MCQeasy

Which IPv4 multicast address range is designated for Source-Specific Multicast (SSM) operations according to IANA standards?

A.224.0.1.0/24
B.224.0.0.0/24
C.239.0.0.0/8
D.232.0.0.0/8
AnswerD

232.0.0.0/8 is the IANA-designated SSM range, letting receivers specify both source and group in IGMPv3 or MLDv2 joins. This satisfies the stem's requirement for the standard SSM block, unlike the ASM ranges 224.0.0.0/4 or the administratively scoped 239.0.0.0/8.

Why this answer

The range 232.0.0.0/8 is reserved for Source-Specific Multicast (SSM) by IANA.

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22
MCQhard

An enterprise design uses PIM sparse-mode with a BSR. An engineer notices that the router has successfully elected a BSR, but no Candidate-RP messages are being processed. Which operational command should the engineer use to verify the BSR candidate information and elected BSR address on the router?

A.show igmp bsr
B.show pim bsr statistics
C.show msdp bsr-state
D.show multicast bsr
AnswerB

This command displays bootstrap messages received, elected BSR address, and candidate RP information.

Why this answer

The 'show pim bsr local' or 'show pim bsr' commands display information regarding the BSR state, elected BSR, and received bootstrap messages.

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23
MCQmedium

An administrator wants to configure an MSDP peer relationship on a Junos device and ensure that the MD5 password authentication is applied to the TCP session. Where is the MD5 authentication key configured for an MSDP peer?

A.set system authentication-key <key>
B.set protocols pim peer <address> authentication-key <key>
C.set protocols msdp peer <address> authentication-key <key>
D.set routing-options msdp authentication-key <key>
AnswerC

Junos configures MSDP TCP MD5 authentication under the peer hierarchy using authentication-key, which applies the key to the TCP session with that specific peer. This satisfies the requirement to secure the MSDP peer relationship's TCP session.

Why this answer

MSDP authentication keys are configured under the specific MSDP peer statement using the authentication-key option.

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24
Multi-Selecthard

An engineer is troubleshooting a multicast forwarding issue where data from a specific source is not reaching receivers in a remote PIM sparse-mode domain. Which THREE operational commands and diagnostic steps should be used to verify the multicast forwarding state and RPF path on a Junos router? (Choose three)

Select 3 answers
A.Run 'show ospf database multicast' to verify LSA type 6 propagation.
B.Run 'show pim join' to inspect upstream neighbor information and verify the RPF interface for the source.
C.Run 'show igmp group' to verify that receivers have successfully joined the multicast group on the local interface.
D.Run 'show bgp summary multicast-unicast' to verify BGP routing tables for multicast RPF checks.
E.Run 'show multicast route' to verify if (S,G) or (*,G) entries exist and check packet forwarding counters.
AnswersB, C, E

The 'show pim join' command displays PIM join state and confirms the upstream RPF neighbor toward the source or RP.

Why this answer

Option B is correct because 'show pim join' displays the PIM join state, including the upstream neighbor (RPF neighbor) and the incoming/RPF interface for each (S,G) or (*,G) entry, which is exactly what is needed to confirm the RPF path toward the source in a PIM sparse-mode domain. Option C is correct because 'show igmp group' verifies that receivers on the local segment have actually sent IGMP joins for the group, confirming the last-hop router has the group membership needed to build the multicast forwarding state. Option E is correct because 'show multicast route' shows the installed (S,G)/(*,G) forwarding entries along with their incoming and outgoing interfaces and packet counters, letting the engineer confirm whether traffic is being forwarded and where it may be dropping.

Option A is not correct because OSPF LSA type 6 (group-membership LSA) is MOSPF-specific and is not used for RPF checks in a PIM sparse-mode domain. Option D is not correct because there is no 'show bgp summary multicast-unicast' command, and multicast RPF lookups in Junos use the unicast routing table (inet.0) or an explicit multicast RPF table, not a BGP multicast-unicast summary.

Exam trap

JNCIP-ENT often tests the confusion between multicast and unicast routing tables, and candidates may incorrectly assume BGP or OSPF multicast LSAs are used for RPF; the trap is selecting invalid or non-existent commands.

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25
Multi-Selectmedium

Which TWO statements are correct regarding IGMP version 2 (IGMPv2) features compared to IGMPv1? (Choose two)

Select 2 answers
A.IGMPv2 relies entirely on group membership timeout for leaving groups.
B.IGMPv2 includes a querier election mechanism among multiple routers on a subnet.
C.IGMPv2 introduces explicit Leave Group messages to reduce leave latency.
D.IGMPv2 supports source-specific filtering lists (include/exclude).
E.IGMPv2 requires PIM sparse-mode to be enabled on all participating hosts.
AnswersB, C

IGMPv2 introduces a querier election process, where routers on the same subnet exchange queries and the lowest IP address wins, becoming the sole querier. IGMPv1 has no such election, relying instead on the multicast routing protocol (PIM) to designate the querier, so this feature directly satisfies the comparison the stem requests.

Why this answer

Option B is correct because IGMPv2 adds a querier election process: when multiple multicast routers exist on the same subnet, the one with the lowest source IP address on that subnet is elected as the querier, whereas IGMPv1 designated the querier via the multicast routing protocol (e.g., PIM). Option C is correct because IGMPv2 introduces the explicit Leave Group message (type 0x17), sent to the all-routers address 224.0.0.2, which allows the querier to send a group-specific query and prune the group quickly instead of waiting for the full group membership timeout. Option A is wrong because IGMPv2 specifically reduces reliance on the membership timeout by using the Leave Group message, though the timeout still exists as a fallback.

Option D is wrong because source-specific include/exclude filtering is an IGMPv3 feature, not IGMPv2. Option E is wrong because IGMPv2 is a host-to-router protocol that does not require PIM sparse-mode on hosts; PIM is a router-to-router multicast routing protocol.

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26
Multi-Selecthard

An enterprise network uses MBGP (Multicast BGP) alongside PIM sparse-mode. Which THREE statements accurately describe the function of MBGP in a multicast environment? (Choose three)

Select 3 answers
A.MBGP allows the multicast routing topology to be different from the unicast routing topology.
B.MBGP replaces the function of MSDP by sharing source-active states between RPs.
C.MBGP forwards multicast data packets directly across autonomous systems.
D.MBGP uses Address Family Identifier (AFI) and Subsequent Address Family Identifier (SAFI) extensions.
E.MBGP provides the routing path information used by PIM routers to perform RPF checks.
AnswersA, D, E

MBGP carries separate unicast and multicast Network Layer Reachability Information, letting RPF checks follow a distinct multicast topology rather than mirroring the unicast path. This satisfies the stem's requirement that multicast routing diverge from unicast routing, which plain BGP cannot achieve since it advertises only one reachability set.

Why this answer

MBGP (Multicast BGP, defined in RFC 4760/2858) is an extension of BGP that carries multicast routing information in a separate RIB from unicast, so option A is correct: it lets the multicast topology diverge from the unicast topology (e.g., different paths or next hops for RPF). Option D is correct because MBGP is implemented through multiprotocol BGP extensions using the Address Family Identifier (AFI 1 = IPv4, 2 = IPv6) and Subsequent Address Family Identifier (SAFI 1 = unicast, 2 = multicast, 3 = both) to distinguish NLRI for multicast from unicast. Option E is correct because PIM relies on the unicast/multicast RIB populated by MBGP to determine the RPF interface and RPF neighbor toward the source or RP; MBGP supplies that path information for interdomain RPF.

Option B is wrong because MSDP is a separate protocol that shares source-active (SA) messages between RPs across domains, and MBGP does not replace it. Option C is wrong because MBGP is a control-plane routing protocol only; it does not forward multicast data packets, which is the job of PIM and the multicast forwarding tables.

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27
MCQmedium

An engineer needs to view the MSDP Source-Active (SA) cache on a Junos router to verify which sources are currently active across different PIM domains. Which operational command should be executed?

A.show multicast source-cache
B.show bgp msdp active
C.show pim source-active
D.show msdp source-active
AnswerD

`show msdp source-active` directly queries the MSDP SA cache, listing active sources and their originating PIM domains. This satisfies the requirement to verify which sources are currently active across domains, since the SA cache is precisely the repository MSDP populates from SA messages. Other MSDP commands display peer or statistics data, not cached source entries.

Why this answer

The 'show msdp source-active' command displays the contents of the MSDP SA cache.

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28
MCQhard

An enterprise network uses multiple routing instances with PIM sparse-mode. An engineer needs to configure Inter-AS multicast routing using MSDP. Which component is required to establish MSDP peering across different autonomous systems where BGP is also running?

A.A shared PIM dense-mode tunnel between the AS border routers
B.IGMPv2 proxy configuration on the border routers
C.Static multicast routes for all 224.0.0.0/4 destinations
D.Matching MSDP peer loopback addresses and TCP session establishment with MBGP routing
AnswerD

MSDP peering requires loopback addresses to match on both peers and a TCP session on port 639, with MBGP carrying the multicast routes that resolve the RPF check. That combination enables inter-AS source discovery across autonomous systems running BGP.

Why this answer

MSDP peers can be configured between BGP speakers in different ASs. The MSDP peer address often matches the BGP router ID or loopback, and MBGP supplies the RPF route for the source.

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29
MCQmedium

An enterprise network runs PIM sparse-mode with a static RP configured on all routers. Users on a VLAN report that they can receive multicast streams from external sources, but the internal server 10.10.5.20 streaming to group 239.1.1.1 was just migrated to a new subnet. After the migration, receivers on a different VLAN stop receiving the stream, even though the new subnet is reachable and PIM is enabled on all interfaces. Which configuration element is most likely missing?

A.The first-hop router connected to the new source subnet must have a route to the RP and PIM enabled on the interface facing the source.
B.An MSDP peer relationship must be established between the first-hop router and the RP to carry source information.
C.The RP must be configured with an anycast address so that both the old and new source subnets can register simultaneously.
D.The new source interface must be added under the [edit protocols pim rp static] address configuration as a permitted source.
AnswerA

In PIM sparse-mode, the first-hop router (FHR) adjacent to the source must have PIM enabled on the source-facing interface and a unicast route toward the RP so it can send PIM Register messages encapsulating the source traffic. If the migrated subnet touches a router without PIM on that interface, the source never registers and receivers on the shared tree receive nothing.

Why this answer

PIM sparse-mode requires the last-hop router to join the shared tree toward the RP, and the first-hop router to register active sources with the RP. When a source moves to a new subnet, the router directly attached to that subnet becomes the new first-hop router. It must have PIM enabled on the source-facing interface and a unicast route to the RP so Register messages can be delivered.

Without that, the RP never learns the source and receivers on the shared tree are starved.

Exam trap

The trap here is assuming that multicast forwarding depends only on receiver-side joins and the RP, when the source-side first-hop router must independently register the source with the RP.

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30
MCQmedium

A network engineer must implement Anycast RP using MSDP between two data center routers running Junos OS. Which statement correctly describes a core requirement for MSDP peer establishment?

A.MSDP messages are encapsulated in PIM register packets and sent directly to the multicast group 224.0.0.13.
B.MSDP relies on IGMPv3 source filters to exchange active source state information across administrative domains.
C.MSDP peering sessions require direct physical interface connectivity between the Anycast RP routers.
D.MSDP peer addresses must be reachable via standard unicast routing protocols, and TCP port 639 must be allowed.
AnswerD

MSDP peers establish a TCP session on port 639, so the peer addresses must be reachable through the unicast routing table rather than the Anycast RP address itself. This satisfies the stem's core requirement: each router needs a unique, routable loopback for the MSDP session, distinct from the shared Anycast address.

Why this answer

MSDP sessions run over TCP port 639. Unlike PIM, MSDP peers do not require direct physical connectivity and typically peer using their loopback addresses, requiring an IGP and an underlying unicast route to establish the TCP connection.

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31
MCQmedium

An administrator wants to configure MSDP (Multicast Source Discovery Protocol) between two autonomous system border routers to share active source information. Which configuration hierarchy in Junos is used to define the MSDP peer relationship?

A.[edit routing-options msdp]
B.[edit protocols msdp]
C.[edit protocols pim msdp]
D.[edit protocols bgp group msdp]
AnswerB

MSDP peer relationships are configured under the [edit protocols msdp] hierarchy, where you define each peer with its address and optional parameters such as local address and authentication. This satisfies the stem's requirement to share active source information between the two autonomous system border routers.

Why this answer

MSDP in Junos is configured under the [edit protocols msdp] hierarchy.

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32
MCQhard

An enterprise has deployed MSDP between two independent PIM sparse-mode domains. An administrator notices that Source-Active (SA) messages are looping between MSDP peers. Which Junos mechanism should be configured to prevent SA message loops in an MSDP topology?

A.Configure static RPF routes pointing to the peer loopbacks.
B.Configure an MSDP mesh group using 'set protocols msdp mesh-group <name>'.
C.Enable PIM Dense-Mode on the interconnecting links between the MSDP peers.
D.Apply a TTL scoping boundary on the MSDP TCP sessions.
AnswerB

Mesh groups allow a set of MSDP peers to fully mesh logically; SA messages received from a mesh group peer are not flooded to other members of the same mesh group, preventing loops.

Why this answer

MSDP uses a modified Reverse Path Forwarding (RPF) check for SA messages. To prevent loops in complex topologies, peer RPF flooding rules or MSDP mesh groups are configured using 'set protocols msdp mesh-group'.

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33
MCQeasy

Which IPv4 address is assigned as the all-systems multicast group address, used by routers to query all hosts on a local subnet?

A.224.0.0.1
B.224.0.0.22
C.224.0.0.13
D.224.0.0.2
AnswerA

224.0.0.1 is the all-hosts group on a local subnet, which every IPv4 host joins automatically. Routers send IGMP general queries to this address to poll all hosts, satisfying the stem's requirement for querying every host on the local segment.

Why this answer

224.0.0.1 is the all-hosts (all-systems) multicast group address.

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34
MCQmedium

An engineer configures protocol independent multicast (PIM) sparse-mode on a Junos device and notices that join messages are not reaching the Rendezvous Point (RP). Which CLI command should the engineer use to verify the operational state of the PIM neighbor adjacencies and confirm that the hello messages are successfully exchanged?

A.show pim neighbor
B.show mpls lsp
C.show rpc statistics
D.show igmp group
AnswerA

PIM hello messages build neighbour adjacencies, and joins only propagate once these exist. The show pim neighbor command displays each neighbour's address, interface, uptime and holdtime, confirming whether hellos are being exchanged and revealing why join messages never reach the Rendezvous Point.

Why this answer

The 'show pim neighbor' command is the standard operational command in Junos to verify active PIM neighbor adjacencies, IP addresses, interfaces, and hold timers.

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35
MCQeasy

Which protocol version introduces explicit source inclusion and exclusion lists (TO_EX, TO_IN, IS_IN, IS_EX) in membership reports?

A.IGMPv2
B.IGMPv4
C.IGMPv3
D.IGMPv1
AnswerC

IGMPv3 membership reports carry source filtering, letting hosts specify include (TO_IN, IS_IN) or exclude (TO_EX, IS_EX) source lists. Earlier versions only supported group joins without source selection, so IGMPv3 uniquely satisfies the explicit inclusion and exclusion requirement.

Why this answer

IGMPv2 supports basic group membership, whereas IGMPv3 introduces source-filtering capabilities allowing hosts to specify include or exclude source lists.

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36
Multi-Selecthard

An engineer is troubleshooting multicast forwarding and RPF failures on a Junos routing instance. Which THREE conditions will cause a multicast RPF check failure? (Choose three)

Select 3 answers
A.IGMPv2 leave messages are received on an interface without active listeners.
B.The route to the source points towards a null or reject route.
C.There is no matching route in the unicast routing table or MBGP table for the source IP address.
D.The incoming interface of the multicast packet does not match the outgoing interface of the RPF route towards the source.
E.PIM hello messages are exchanged with an incorrect hold time.
AnswersB, C, D

If the RPF lookup resolves to a reject or discard route, the RPF check fails.

Why this answer

RPF failures occur when the incoming interface for a multicast packet does not match the reverse path towards the source in the routing table, when no route exists, or when the routing table source differs.

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37
Multi-Selecthard

A network engineer is troubleshooting a PIM Sparse-Mode domain where multicast traffic from a source is not reaching receivers. The engineer suspects that the Rendezvous Point (RP) is not receiving PIM Register messages from the First-Hop Router (FHR). Which TWO statements describe reasons why the FHR might fail to send Register messages to the RP? (Choose two.)

Select 2 answers
A.The FHR is not the PIM Designated Router on the source LAN.
B.The FHR does not have a route to the RP address.
C.The FHR is configured with IGMP version 3 instead of version 2.
D.The RP is configured with a lower priority than the FHR.
E.The FHR has not yet received an IGMP join for the group.
AnswersA, B

Only the PIM Designated Router (DR) on the source LAN sends Register messages to the RP. If the FHR is not the DR, it will not send registers. The DR is elected based on PIM priority and highest IP address; if another router is DR, the FHR will not perform registration.

Why this answer

The First-Hop Router sends PIM Register messages to the RP only if it has a unicast route to the RP and is the PIM Designated Router on the source LAN. Without a route, the register cannot be sent. If another router is DR, the FHR will not send registers.

Other factors like IGMP version or RP priority do not affect the FHR's ability to send registers.

Exam trap

The trap here is assuming that IGMP joins are required for the FHR to send registers; in reality, registers are triggered by source traffic, not by receiver joins.

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