JNCIP-ENT IP Multicast — 15 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?

Choose an answer to begin — your selection is scored in the full session.

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

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?

Accepted Answer

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

Answer

show ospf route

Answer

show igmp interface

Answer

show pim join

Question 5

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?

Accepted Answer

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

Answer

[edit routing-options msdp]

Answer

[edit protocols pim msdp]

Answer

[edit protocols bgp group msdp]

Question 6

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?

Accepted Answer

Multicast Source Discovery Protocol (MSDP). 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.

Answer

Protocol Independent Multicast Dense-Mode (PIM-DM)

Answer

IGMPv3 snooping

Answer

Multicast BGP (MBGP)

Question 7

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

Accepted Answer

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

Answer

224.0.1.0/24

Answer

224.0.0.0/24

Answer

239.0.0.0/8

Question 8

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?

Accepted Answer

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

Answer

show mpls lsp

Answer

show rpc statistics

Answer

show igmp group

Question 9

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 10

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 11

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 12

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 13

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?

Accepted Answer

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

Answer

show multicast source-cache

Answer

show bgp msdp active

Answer

show pim source-active

Question 14

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 15

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

Accepted Answer

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

Answer

show multicast heap

Answer

show msdp SA-cache

Answer

show pim rp statistics