JNCIP-ENT IP Multicast Practice Test 4 — 15 Questions

Question 1

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

Accepted Answer

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

Answer

The BSR acts as the data encapsulation point for multicast sources.

Answer

The BSR forwards multicast data packets directly to receivers.

Answer

The BSR is required to establish MSDP sessions between autonomous systems.

Question 2

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)

Accepted Answer

The route to the source points towards a null or reject route.. 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.

Answer

IGMPv2 leave messages are received on an interface without active listeners.

Answer

PIM hello messages are exchanged with an incorrect hold time.

Question 3

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)

Accepted Answer

MBGP allows the multicast routing topology to be different from the unicast routing topology.. 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.

Answer

MBGP replaces the function of MSDP by sharing source-active states between RPs.

Answer

MBGP forwards multicast data packets directly across autonomous systems.

Question 4

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)

Accepted Answer

It conserves bandwidth on switch links by filtering unwanted multicast streams.. 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.

Answer

It automatically acts as the PIM Rendezvous Point for the VLAN.

Answer

It translates IPv4 multicast addresses to IPv6 multicast addresses.

Answer

It replaces PIM sparse-mode on Layer 3 core routers.

Question 5

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?

Accepted Answer

set protocols igmp interface irb.10 version 3. IGMP version selection on Junos interfaces is configured under protocols igmp interface.

Answer

set protocols pim interface irb.10 igmp-version 3

Answer

set interfaces irb.10 family inet igmp-version v3

Answer

set routing-options multicast igmp-version 3

Question 6

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?

Accepted Answer

MSDP peer addresses must be reachable via standard unicast routing protocols, and TCP port 639 must be allowed.. 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.

Answer

MSDP messages are encapsulated in PIM register packets and sent directly to the multicast group 224.0.0.13.

Answer

MSDP relies on IGMPv3 source filters to exchange active source state information across administrative domains.

Answer

MSDP peering sessions require direct physical interface connectivity between the Anycast RP routers.

Question 7

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?

Accepted Answer

Configure an MSDP mesh group using 'set protocols msdp mesh-group <name>'.. 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'.

Answer

Configure static RPF routes pointing to the peer loopbacks.

Answer

Enable PIM Dense-Mode on the interconnecting links between the MSDP peers.

Answer

Apply a TTL scoping boundary on the MSDP TCP sessions.

Question 8

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?

Accepted Answer

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

Answer

239.0.0.0/8

Answer

224.0.0.0/24

Answer

224.0.1.0/24

Question 9

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)

Accepted Answer

Run 'show pim join' to inspect upstream neighbor information and verify the RPF interface for the source.. 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.

Answer

Run 'show ospf database multicast' to verify LSA type 6 propagation.

Answer

Run 'show bgp summary multicast-unicast' to verify BGP routing tables for multicast RPF checks.

Question 10

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?

Accepted Answer

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.. 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.

Answer

It immediately sends a Register-Stop to the first-hop router and waits for the source to send native multicast traffic.

Answer

It forwards the Register message to the BSR to request a new RP mapping for the group.

Answer

It immediately decapsulates the Register message and forwards the multicast data to the shared tree.

Question 11

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?

Accepted Answer

Configure the group in a PIM source-specific multicast (SSM) group range on all routers in the path.. 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.

Answer

Configure a static RP for the group with the address of the local router's loopback interface.

Answer

Configure the group as a PIM sparse-dense-mode group so it uses source-specific trees.

Answer

Enable PIM dense-mode on the interfaces facing the multicast receivers for the group.

Question 12

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.)

Accepted Answer

The FHR is not the PIM Designated Router on the source LAN.. 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.

Answer

The FHR is configured with IGMP version 3 instead of version 2.

Answer

The RP is configured with a lower priority than the FHR.

Answer

The FHR has not yet received an IGMP join for the group.

Question 13

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?

Accepted Answer

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.. 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.

Answer

An MSDP peer relationship must be established between the first-hop router and the RP to carry source information.

Answer

The RP must be configured with an anycast address so that both the old and new source subnets can register simultaneously.

Answer

The new source interface must be added under the [edit protocols pim rp static] address configuration as a permitted source.

Question 14

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?

Accepted Answer

Ensure PIM is enabled on the interface toward 10.10.10.10 so the router can build the (S,G) tree.. 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.

Answer

Add a static IGMP group membership for 239.5.5.5 on the VLAN 100 interface.

Answer

Configure an RP for the group so the shared tree can be used for delivery.

Answer

Increase the IGMP query interval on VLAN 100 so the receiver reports are refreshed more often.

Question 15

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?

Accepted Answer

Enable IGMP on the interface facing the VLANs in addition to PIM sparse-mode.. 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.

Answer

Enable PIM dense-mode on the interface so IGMP reports are flooded to all routers.

Answer

Enable IGMP snooping on the router interface facing the VLANs.

Answer

Configure a static IGMP group join for each multicast group on the router interface.