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CCNA IP Multicast Questions

47 questions · IP Multicast topic · All types, answers revealed

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1
MCQhard

During an audit of a multiregion enterprise network using PIM Sparse-Mode, an engineer needs to ensure that only designated Bootstrap Routers (BSRs) can inject candidate-RP information into the domain. Which Junos configuration feature should be applied on the core routers to secure the BSR domain?

A.Configure an RP-reachability policy under protocols pim static rp.
B.Configure 'set protocols pim bsr-candidate interface' with a strict metric.
C.Configure 'set protocols pim interface <interface> bsr-edge' on downstream boundary interfaces.
D.Configure a firewall filter on the loopback interface matching PIM protocol traffic destined for 224.0.0.13.
AnswerC

The bsr-edge statement prevents BSR messages from crossing into or out of specific interfaces, establishing a security boundary for the PIM domain.

Why this answer

To protect the PIM domain from rogue BSR messages or unauthorized candidate-RP announcements, Junos allows configuring BSR edge boundaries or using a bsr-candidate policy to filter incoming bootstrap messages.

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2
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

This command displays MSDP peer addresses, connection states, and uptime.

Why this answer

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

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3
MCQmedium

An administrator wants to configure a static Rendezvous Point (RP) with IP address 192.168.100.1 for all multicast groups on a Junos router. Which configuration accomplishes this?

A.set routing-options multicast rp 192.168.100.1
B.set protocols pim static-rp address 192.168.100.1
C.set protocols igmp rp address 192.168.100.1
D.set protocols pim rp static address 192.168.100.1
AnswerD

This configures a static RP address for all groups under PIM.

Why this answer

Static RPs are defined under protocols pim rp static address. Group ranges can also be specified.

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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 C-RP info and floods bootstrap messages domain-wide.

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

Candidate RP settings, including local address and group ranges, are configured under protocols pim candidate-rp.

Why this answer

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

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6
MCQmedium

An engineer wants to restrict IGMP membership reports to only accept version 2 on a specific VLAN interface configured on an MX Series router. Which configuration statement achieves this requirement?

A.set protocols pim interface vlan.10 igmp-version 2
B.set protocols igmp interface vlan.10 version 2
C.set routing-options multicast igmp-version 2 interface vlan.10
D.set interfaces vlan.10 igmp-version 2
AnswerB

This explicitly forces the IGMP version on the specified interface to version 2.

Why this answer

Junos allows configuring specific IGMP versions per interface under protocols igmp interface.

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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

PIM-SM uses explicit joins to build distribution trees rather than flooding and pruning.

Why this answer

PIM sparse-mode assumes that multicast traffic is not wanted across all segments by default, requiring explicit join messages. It relies heavily on a Rendezvous Point (RP) to connect sources and receivers initially.

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8
MCQhard

A network engineer troubleshoots an issue where multicast data packets are being dropped due to an RPF (Reverse Path Forwarding) check failure. The unicast routing table uses OSPF, but MBGP is deployed for multicast routing. Which operational command should the engineer use to verify the multicast RPF path for a specific source IP?

A.show msdp rpf 192.0.2.1
B.show pim rpf-table 192.0.2.1
C.show route rpf 192.0.2.1
D.show multicast rpf-failure
AnswerC

The 'show route rpf' command displays the RPF lookup results and path used by multicast routing.

Why this answer

When MBGP is used for multicast RPF separate from unicast routing, the command 'show route rpf <source-ip>' helps check which routing table and next-hop is used for the multicast RPF check.

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9
Multi-Selectmedium

An enterprise architect is designing an IP multicast solution using PIM Sparse-Mode and needs to configure a Rendezvous Point (RP) redundantly using Auto-RP. However, Junos OS does not natively support listening to Cisco Auto-RP discovery and announcement messages without specific helper configurations. Which TWO configuration steps are required on Junos to interoperate with or process Auto-RP messages? (Choose two)

Select 2 answers
A.Configure PIM Dense-Mode on interfaces receiving Auto-RP announcement and discovery multicast groups (224.0.1.39 and 224.0.1.40).
B.Enable 'auto-rp compatibility' under the global [edit protocols pim] hierarchy.
C.Set the PIM mode to SSM-only across all core interfaces.
D.Enable MSDP peering between the Auto-RP mapping agent and the Junos router.
E.Configure static RP mappings for the Auto-RP well-known multicast groups 224.0.1.39 and 224.0.1.40.
AnswersA, E

Auto-RP messages use dense-mode flooding over well-known addresses 224.0.1.39 and 224.0.1.40, requiring those groups to operate in dense mode or be statically handled.

Why this answer

Junos does not natively run Auto-RP (Cisco proprietary). To support Auto-RP environments, Junos routers can be configured to map Auto-RP groups using static RP or by using RPM/helper statements, or by mapping Auto-RP group addresses (224.0.1.39 and 224.0.1.40) into PIM dense-mode or static mappings if supported. Specifically, standard deployments map the Auto-RP well-known group addresses or use static RP configurations since Junos natively relies on standard BSR.

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10
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

This command displays the multicast groups and receiver memberships learned via IGMP.

Why this answer

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

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11
MCQhard

In an enterprise network running PIM sparse-mode, an engineer notices that multicast traffic is switched from the shared tree (*,G) to the source-specific tree (S,G) prematurely, causing micro-bursts on core links. Which command disables this automatic switchover behavior on a Junos router?

A.set routing-options multicast spt-mode disable
B.set protocols pim disable-spt-switchover
C.set protocols igmp spt-threshold 0
D.set protocols pim spt-threshold infinity
AnswerD

Setting the SPT threshold to infinity prevents the last-hop router from switching to the source-specific tree, keeping it on the shared tree.

Why this answer

By default, last-hop routers switch from (*,G) to (S,G) upon receiving the first packet from source S. To prevent this, the 'spt-threshold infinity' command is configured under [edit protocols pim].

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12
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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13
MCQhard

An enterprise network uses PIM sparse-mode across multiple routing instances. An administrator notices that source registration messages are looping between the designated router (DR) and the RP. Which configuration statement under [edit protocols pim] will prevent the DR from continuously encapsulating and sending register messages when no receivers are joined?

A.set protocols pim interface all no-bsr
B.set protocols pim rp static address 192.168.1.1 register-policy REJECT-REG
C.set protocols pim rp static address 192.168.1.1 no-registration-suppression
D.set protocols pim rp static address 192.168.1.1
AnswerD

Configuring a static RP properly ensures the DR knows the unicast destination for register encapsulation, and Junos handles register-stop suppression natively when configured correctly.

Why this answer

Using register-suppression or configuring an MSDP peer is common, but on the Junos DR side, ensuring proper register-policy or verifying register-stop timers helps. However, Juniper implements register-suppression by default via register-stop messages from the RP. To alter register behavior, register-policy can be applied.

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14
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

This command displays the active multicast forwarding cache and routing state.

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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15
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

The 'version 3' statement under protocols igmp interface explicitly sets the IGMP version to 3.

Why this answer

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

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16
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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17
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

This command shows the active RP set and how each RP was discovered.

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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18
Multi-Selecthard

An enterprise engineer is configuring Multicast Source Discovery Protocol (MSDP) on a Junos device. Which THREE statements accurately describe MSDP behavior and functions? (Choose three)

Select 3 answers
A.MSDP uses Source-Active (SA) messages to advertise active multicast sources to peer RPs.
B.MSDP is required for Anycast RP deployments within the same or different PIM domains.
C.MSDP replaces PIM sparse-mode for forwarding multicast data traffic to receivers.
D.MSDP peer connections are maintained via reliable TCP sessions.
E.MSDP runs directly over IP protocol number 46.
AnswersA, B, D

SA messages contain the source IP, group IP, and originating RP address.

Why this answer

MSDP is used between RPs to share active sources, uses TCP for transport, and uses SA (Source-Active) messages.

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19
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

By pruning multicast streams from links without receivers, network bandwidth is conserved.

Why this answer

IGMP snooping inspects IGMP traffic to constrain multicast traffic to ports with active receivers, preventing unnecessary flooding on non-listening ports.

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20
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

The 232.0.0.0/8 block is allocated specifically for Source-Specific Multicast applications.

Why this answer

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

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21
Multi-Selecthard

An administrator is designing a high-availability PIM sparse-mode network. Which THREE mechanisms are used to provide redundancy for Rendezvous Points (RPs)? (Choose three)

Select 3 answers
A.Anycast RP with MSDP peering between multiple RPs
B.IGMP snooping querier election redundancy across core switches
C.Static RP configuration with multiple backup RP IP addresses configured on every router
D.MBGP multipath routing for RPF path selection
E.Bootstrap Router (BSR) with multiple Candidate-RPs
AnswersA, D, E

Anycast RP combined with MSDP synchronizes source registrations across redundant RPs.

Why this answer

RP redundancy is typically achieved using static Anycast RP with MSDP, Bootstrap Router (BSR) dynamic discovery with multiple Candidate RPs, or Auto-RP (vendor-specific).

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22
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

Configuring the BSR candidate parameters and local interface address is done under protocols pim bsr.

Why this answer

BSR functionality on Junos is configured under protocols pim bsr.

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23
Multi-Selectmedium

Which TWO statements correctly describe the role of the Designated Router (DR) on a multi-access network running PIM sparse-mode? (Choose two)

Select 2 answers
A.The DR elects the IGMP querier for the VLAN segment.
B.The DR maintains the MSDP Source-Active cache for the entire AS.
C.The DR sends PIM join and prune messages towards the RP on behalf of local receivers when necessary.
D.The DR encapsulates multicast data packets from sources into PIM register messages sent to the RP.
E.The DR floods all multicast traffic across the multi-access segment by default.
AnswersC, D

The receiver-side DR acts on behalf of local hosts to join shared or source trees.

Why this answer

The PIM DR is responsible for sending register messages to the RP on behalf of sources and sending join/prune messages on behalf of receivers on a shared LAN segment.

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24
MCQhard

During multicast troubleshooting, an engineer notices that a router is not accepting MSDP Source-Active messages from a specific peer. Where should an export policy be applied to control which SA messages are sent or accepted via MSDP?

A.set protocols msdp peer <address> import <policy-name>
B.set routing-options msdp-policy <policy-name>
C.set protocols pim msdp-import <policy-name>
D.set protocols bgp group msdp export <policy-name>
AnswerA

Applying an import policy under the specific MSDP peer controls which incoming SA messages are accepted.

Why this answer

MSDP policies in Junos are applied directly under the specific MSDP peer configuration or globally under protocols msdp export/import.

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25
MCQhard

An administrator configures MSDP peering between two routers. After configuration, the MSDP session remains in the 'Connect' or 'Active' state and never transitions to 'Established'. Which underlying protocol dependency must be verified and operational for MSDP sessions to establish?

A.TCP connectivity on port 639 between the MSDP peers
B.MBGP unicast routing tables synchronized
C.PIM dense-mode adjacency between the peers
D.IGMPv3 snooping enabled on intermediate switches
AnswerA

MSDP runs over TCP using port 639; if TCP fails, the session cannot reach the Established state.

Why this answer

MSDP relies directly on TCP (TCP port 639) to establish peer connections. If TCP connectivity fails, the MSDP state will not reach Established.

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26
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

The 232.0.0.0/8 address block is specifically allocated for Source-Specific Multicast.

Why this answer

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

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27
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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28
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

This configures the MD5 password for the TCP connection to the specified MSDP peer.

Why this answer

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

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29
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

To troubleshoot multicast traffic forwarding and RPF failures in Junos, operators check the multicast forwarding cache using 'show multicast route', verify the upstream RPF neighbor using 'show pim join', and inspect IGMP membership states.

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30
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 elects the router with the lowest IP address as the querier.

Why this answer

IGMPv2 introduced explicit leave messages (Leave Group) and a designated querier election mechanism, unlike IGMPv1 which relied on timeout expiration.

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31
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

Because MBGP maintains separate tables (via IPv4 multicast AFI/SAFI), paths can be optimized differently from unicast.

Why this answer

MBGP provides separate multicast routing information for RPF checks, uses address families (AFI/SAFI), and allows multicast topology to differ from unicast topology.

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32
MCQeasy

Which configuration statement enables PIM sparse-mode globally across all interfaces in a Junos routing instance?

A.set routing-options multicast pim-enable
B.set protocols multicast enable
C.set protocols pim interface all
D.set protocols pim interface all mode sparse
AnswerC

Enabling PIM on 'interface all' turns on PIM sparse-mode across all router interfaces.

Why this answer

In Junos, PIM can be enabled on individual interfaces or globally by specifying 'interface all' under protocols pim.

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33
Multi-Selectmedium

An enterprise network administrator is configuring PIM Sparse-Mode and needs to control which multicast groups are allowed to be joined or forwarded through the network. Which THREE methods or configuration elements can be used in Junos OS to filter multicast join messages or control group memberships? (Choose three)

Select 3 answers
A.Configure a firewall filter family inet filter-name on the loopback interface matching destination port 639.
B.Apply a bridge-domain filter under [edit bridge-domains] blocking destination MAC address 01:00:5E:00:00:01.
C.Configure an IGMP access policy under [edit protocols igmp interface <name> policy] to restrict local host group memberships.
D.Apply a policy statement under [edit protocols pim join-policy] to filter incoming (*,G) and (S,G) joins.
E.Configure SSM mapping using [edit protocols igmp ssm-mapping] to translate standard IGMPv2 joins into SSM range joins.
AnswersC, D, E

IGMP policies can be applied on interfaces to control which groups directly connected hosts are permitted to join.

Why this answer

In Junos, multicast group filtering can be achieved by applying policy frameworks to PIM joins, configuring IGMP access-lists or policies to restrict host joins, and setting SSM mapping filters.

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34
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

This command shows the active source entries learned or advertised via MSDP.

Why this answer

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

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35
Multi-Selectmedium

Which TWO statements are true regarding Source-Specific Multicast (SSM) operation in Junos? (Choose two)

Select 2 answers
A.SSM eliminates the need for Rendezvous Points (RPs) and MSDP.
B.SSM requires PIM dense-mode to flood traffic to all routers.
C.SSM operates within the 224.0.0.0/24 multicast range.
D.SSM uses (*,G) shared trees exclusively for distribution.
E.SSM requires IGMPv3 on receiver interfaces to support source-filter membership reports.
AnswersA, E

Since receivers join directly to (S,G), RPs and MSDP are not needed for SSM.

Why this answer

SSM uses the 232.0.0.0/8 range and requires IGMPv3 (or MLDv2 for IPv6) to allow hosts to specify source addresses directly, bypassing the need for an RP.

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36
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

Inter-AS MSDP requires valid TCP peering between RPs and MBGP routing to ensure RPF validation across AS boundaries.

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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37
MCQmedium

An engineer is troubleshooting PIM Sparse-Mode on a Junos device and notices that source traffic is not switching from the shared tree (*,G) to the shortest path tree (S,G) at the Last-Hop Router. Which configuration statement on the Junos routing instance allows adjusting the threshold for this switchover behavior?

A.set routing-options multicast spt-lifetime 0
B.set protocols pim switchover-delay 0
C.set protocols igmp ssm-mapping
D.set protocols pim spt-threshold infinity
AnswerD

Setting the spt-threshold to infinity forces the router to remain on the rendezvous point shared tree (*,G) indefinitely.

Why this answer

By default, Junos switches from the (*,G) shared tree to the (S,G) shortest path tree immediately upon receiving the first data packet from a source. To prevent this or adjust the behavior, operators use the 'spt-threshold' statement under protocols pim.

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38
MCQmedium

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

A.show pim rps
B.show igmp group
C.show multicast route
D.show msdp summary
AnswerA

The 'show pim rps' operational command displays all active Rendezvous Points and how they were learned (static, BSR, etc.).

Why this answer

To check the dynamic RP mappings learned via BSR or static configuration, the command 'show pim join' or 'show pim rps' is used. Specifically, 'show pim rps' displays the active RP database.

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39
MCQhard

An administrator troubleshooting an IGMP snooping issue on an EX Series switch notices that multicast traffic is flooding all ports in a VLAN. Which Junos command verifies the IGMP snooping status and active querier on a specific VLAN?

A.show protocols igmp snooping vlan
B.show ethernet-switching igmp-snooping
C.show igmp-snooping membership vlan vlan-name
D.show bridge igmp-snooping querier
AnswerC

This command shows IGMP snooping group memberships and querier status for the specified VLAN.

Why this answer

On Juniper EX Series switches, IGMP snooping operational state and querier details per VLAN are displayed using 'show igmp-snooping membership' or 'show igmp-snooping statistics'.

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40
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 uses TCP (port 639) for transport, meaning underlying unicast routing must be operational between the peer loopbacks.

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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41
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 parameters and local address configurations are placed under protocols msdp.

Why this answer

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

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42
MCQmedium

An enterprise administrator wants to limit PIM sparse-mode join messages to prevent unauthorized sources from registering. Where should a policy be applied to filter PIM join/prune messages in Junos?

A.set protocols pim import <policy-name>
B.set protocols igmp import <policy-name>
C.set routing-options pim-policy <policy-name>
D.set interfaces all unit 0 family pim filter input <policy-name>
AnswerA

Applying an import policy under [edit protocols pim] filters incoming PIM join and prune messages.

Why this answer

PIM join/prune filtering is accomplished by applying a import policy under protocols pim.

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43
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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44
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 standard multicast address representing all systems on the subnet.

Why this answer

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

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45
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

This command displays all active PIM neighbors, interfaces, and uptime, which confirms hello message exchange.

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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46
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 added support for source filtering, allowing receivers to specify sources they want to receive or block.

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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47
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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