JNCIP-ENT IP Multicast — Timed 20 Questions

Question 1

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?

20 minute time limit — choose an answer to begin.

Accepted Answer

set protocols pim spt-threshold infinity. 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].

Answer

set routing-options multicast spt-mode disable

Answer

set protocols pim disable-spt-switchover

Answer

set protocols igmp spt-threshold 0

Question 2

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?

Accepted Answer

set protocols pim rp static address 192.168.1.1. 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.

Answer

set protocols pim interface all no-bsr

Answer

set protocols pim rp static address 192.168.1.1 register-policy REJECT-REG

Answer

set protocols pim rp static address 192.168.1.1 no-registration-suppression

Question 3

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?

Accepted Answer

set protocols igmp interface vlan.10 version 2. Junos allows configuring specific IGMP versions per interface under protocols igmp interface.

Answer

set protocols pim interface vlan.10 igmp-version 2

Answer

set routing-options multicast igmp-version 2 interface vlan.10

Answer

set interfaces vlan.10 igmp-version 2

Question 4

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?

Accepted Answer

set protocols pim rp static address 192.168.100.1. Static RPs are defined under protocols pim rp static address. Group ranges can also be specified.

Answer

set routing-options multicast rp 192.168.100.1

Answer

set protocols pim static-rp address 192.168.100.1

Answer

set protocols igmp rp address 192.168.100.1

Question 5

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?

Accepted Answer

set protocols pim import <policy-name>. PIM join/prune filtering is accomplished by applying a import policy under protocols pim.

Answer

set protocols igmp import <policy-name>

Answer

set routing-options pim-policy <policy-name>

Answer

set interfaces all unit 0 family pim filter input <policy-name>

Question 6

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

Accepted Answer

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

Answer

set routing-options multicast pim-enable

Answer

set protocols multicast enable

Answer

set protocols pim interface all mode sparse

Question 7

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?

Accepted Answer

show route rpf 192.0.2.1. 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.

Answer

show msdp rpf 192.0.2.1

Answer

show pim rpf-table 192.0.2.1

Answer

show multicast rpf-failure

Question 8

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?

Accepted Answer

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

Answer

MBGP unicast routing tables synchronized

Answer

PIM dense-mode adjacency between the peers

Answer

IGMPv3 snooping enabled on intermediate switches

Question 9

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?

Accepted Answer

set protocols msdp peer

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

Answer

set routing-options msdp-policy <policy-name>

Answer

set protocols pim msdp-import <policy-name>

Answer

set protocols bgp group msdp export <policy-name>

Question 10

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?

Accepted Answer

show igmp-snooping membership vlan vlan-name. 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'.

Answer

show protocols igmp snooping vlan

Answer

show ethernet-switching igmp-snooping

Answer

show bridge igmp-snooping querier

Question 11

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)

Accepted Answer

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

Answer

MSDP replaces PIM sparse-mode for forwarding multicast data traffic to receivers.

Answer

MSDP runs directly over IP protocol number 46.

Question 12

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)

Accepted Answer

Anycast RP with MSDP peering between multiple RPs. 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).

Answer

IGMP snooping querier election redundancy across core switches

Answer

Static RP configuration with multiple backup RP IP addresses configured on every router

Question 13

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

Accepted Answer

SSM eliminates the need for Rendezvous Points (RPs) and MSDP.. 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.

Answer

SSM requires PIM dense-mode to flood traffic to all routers.

Answer

SSM operates within the 224.0.0.0/24 multicast range.

Answer

SSM uses (*,G) shared trees exclusively for distribution.

Question 14

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

Accepted Answer

The DR sends PIM join and prune messages towards the RP on behalf of local receivers when necessary.. 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.

Answer

The DR elects the IGMP querier for the VLAN segment.

Answer

The DR maintains the MSDP Source-Active cache for the entire AS.

Answer

The DR floods all multicast traffic across the multi-access segment by default.

Question 15

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?

Accepted Answer

set protocols pim spt-threshold infinity. 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.

Answer

set routing-options multicast spt-lifetime 0

Answer

set protocols pim switchover-delay 0

Answer

set protocols igmp ssm-mapping

Question 16

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?

Accepted Answer

Configure 'set protocols pim interface <interface> bsr-edge' on downstream boundary interfaces.. 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.

Answer

Configure an RP-reachability policy under protocols pim static rp.

Answer

Configure 'set protocols pim bsr-candidate interface' with a strict metric.

Answer

Configure a firewall filter on the loopback interface matching PIM protocol traffic destined for 224.0.0.13.

Question 17

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)

Accepted Answer

Configure PIM Dense-Mode on interfaces receiving Auto-RP announcement and discovery multicast groups (224.0.1.39 and 224.0.1.40).. 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.

Answer

Enable 'auto-rp compatibility' under the global [edit protocols pim] hierarchy.

Answer

Set the PIM mode to SSM-only across all core interfaces.

Answer

Enable MSDP peering between the Auto-RP mapping agent and the Junos router.

Question 18

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?

Accepted Answer

show pim rps. 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.

Answer

show igmp group

Answer

show multicast route

Answer

show msdp summary

Question 19

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)

Accepted Answer

Configure an IGMP access policy under [edit protocols igmp interface policy] to restrict local host group memberships.. Option C is correct because an IGMP access policy applied under [edit protocols igmp interface policy] lets the router accept or reject IGMP membership reports from directly attached hosts, thereby restricting which multicast groups local receivers may join. Option D is correct because [edit protocols pim join-policy] applies a routing policy to incoming PIM (*,G) and (S,G) join/prune messages, allowing the administrator to filter which groups or sources PIM will build forwarding state for. Option E is correct because IGMP SSM mapping under [edit protocols igmp ssm-mapping] translates IGMPv1/v2 group joins into (S,G) joins within the SSM range (232.0.0.0/8 by default), effectively controlling which source-specific group memberships are permitted. Option A is not correct because destination port 639 is not a multicast control protocol port (IGMP uses IP protocol 2, PIM uses protocol 103), so a family inet firewall filter matching TCP/UDP port 639 would not filter join messages. Option B is not correct because 01:00:5E:00:00:01 is the Ethernet MAC mapping for 224.0.0.1 (all-hosts), and a bridge-domain filter on that MAC does not filter IGMP/PIM join messages or control PIM-SM group membership in a routed enterprise network.

Answer

Configure a firewall filter family inet filter-name on the loopback interface matching destination port 639.

Answer

Apply a bridge-domain filter under [edit bridge-domains] blocking destination MAC address 01:00:5E:00:00:01.

Question 20

A Junos router is configured with PIM sparse mode and acts as the Rendezvous Point (RP) for the multicast group 239.1.1.1. The network administrator notices that the RP has no (S,G) state for a particular source, yet receivers on the shared tree (*,G) are receiving traffic from that source. Which statement explains this behavior?

Accepted Answer

The source's first-hop router has not sent a PIM register message, so the RP has no (S,G) state, but traffic is still flowing because the RP is also the last-hop router for the group.. In PIM sparse mode, the RP normally maintains (S,G) state for active sources to forward traffic down the shared tree. However, if the RP is also the last-hop router for the group, it will join the shared tree and receive multicast traffic directly from the source's first-hop router via the shared tree. In this scenario, the first-hop router does not need to send PIM register messages because the RP is already on the shared tree, so the RP has no (S,G) state. This is a valid and efficient operation.

Answer

The RP is receiving multicast traffic from the source via a shared tree that was built without the RP's involvement.

Answer

The RP is using the shortest-path tree (SPT) for the source, which bypasses the shared tree.

Answer

The source's first-hop router is not registering with the RP because it is directly connected to the RP.