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Read each scenario carefully and choose your answer before revealing the explanation. Then check why your choice was right or wrong. Repeat until the reasoning feels automatic.

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350-401 · topic practice

IP Multicast practice questions

Practise ENCOR 350-401 IP Multicast practice questions — original exam-style scenarios with answer choices, explanations, and analysis of common mistakes.

Courseiva uses original exam-style practice questions designed for learning and revision. The goal is to understand the concepts, recognise exam patterns, and improve through explanations — not memorise copied exam dumps.

Reviewed byJohnson Ajibi· MSc IT Security

20 questionsDomain: IP Multicast

Practice 10 questions Browse domain →

What the exam tests

What to know about IP Multicast

IP Multicast questions test whether you can apply the concept in context, not just recognise a definition.

How the topic appears in realistic exam-style scenarios.

Which detail in the question changes the correct answer.

How to eliminate plausible but wrong options.

How to connect the question back to the wider exam objective.

Watch out for

Common IP Multicast exam traps

▸Answering from memory before reading the full scenario.
▸Missing a constraint such as cost, availability, security, scope or command context.
▸Choosing a broad answer when the question asks for the most specific fix.
▸Ignoring why the wrong options are tempting.

Practice set

IP Multicast questions

20 questions · select your answer, then reveal the explanation

Question 1mediummultiple choice

Open the full VLAN trunking answer →

A network engineer is troubleshooting multicast video distribution across an enterprise campus. The multicast source is connected to a switch that is the PIM Designated Router (DR) on a multi-access segment. Receivers in a different VLAN report that they are not receiving the multicast stream, although the DR shows the correct (S,G) entry. The engineer checks the RPF neighbor for the source and notices that the unicast route to the source points to a different interface than the one where the multicast stream is received. What is the most likely cause of the issue?

Trap 1: The DR is not configured as the RP (Rendezvous Point).

Incorrect because the DR and RP are separate roles; the issue is RPF failure, not RP configuration.

Trap 2: The switchport connected to the source is not configured as a trunk.

Incorrect because the scenario mentions a multi-access segment; trunking is not directly related to RPF failure.

Trap 3: IGMP snooping is disabled on the receiver VLAN.

Incorrect because IGMP snooping affects group membership, not the RPF check for the source.

Study all IP Multicast common traps →

A
The DR is not configured as the RP (Rendezvous Point).
Why wrong: Incorrect because the DR and RP are separate roles; the issue is RPF failure, not RP configuration.
B
The multicast stream is arriving on an interface that is not the RPF interface for the source.
Correct because multicast forwarding requires the incoming interface to match the unicast RPF interface; a mismatch causes the packet to be dropped.
C
The switchport connected to the source is not configured as a trunk.
Why wrong: Incorrect because the scenario mentions a multi-access segment; trunking is not directly related to RPF failure.
D
IGMP snooping is disabled on the receiver VLAN.
Why wrong: Incorrect because IGMP snooping affects group membership, not the RPF check for the source.

Full breakdown with real-world context →

Question 2mediummultiple choice

Review the full OSPF breakdown →

A network engineer is deploying IP multicast in an OSPF-based enterprise network. The network uses PIM sparse mode with a static RP. The engineer notices that multicast traffic from a source to a group is not reaching receivers in a remote subnet, even though the RP is reachable and the receivers have sent IGMP joins. The engineer checks the multicast routing table on the last-hop router and sees that the (S,G) entry is present, but the outgoing interface list (OIL) is empty. What is the most likely reason for the empty OIL?

Trap 1: The multicast source is not registered with the RP.

Incorrect because the source registration is done by the first-hop router, not the last-hop router; the issue is on the receiver side.

Trap 2: PIM dense mode is enabled on the last-hop router.

Incorrect because dense mode would flood traffic, not cause an empty OIL.

Trap 3: The TTL of the multicast packets is too low.

Incorrect because TTL affects packet forwarding, not the OIL population; the OIL is built by PIM joins.

Study all IP Multicast common traps →

A
The RP is not configured on the last-hop router.
Correct because without the RP configured, the router cannot send a PIM join to the RP, so the OIL remains empty.
B
The multicast source is not registered with the RP.
Why wrong: Incorrect because the source registration is done by the first-hop router, not the last-hop router; the issue is on the receiver side.
C
PIM dense mode is enabled on the last-hop router.
Why wrong: Incorrect because dense mode would flood traffic, not cause an empty OIL.
D
The TTL of the multicast packets is too low.
Why wrong: Incorrect because TTL affects packet forwarding, not the OIL population; the OIL is built by PIM joins.

Full breakdown with real-world context →

Question 3hardmultiple choice

Review the full OSPF breakdown →

An engineer is configuring multicast on a Cisco router running IOS-XE. The network uses PIM sparse mode with a static RP at 10.1.1.1. The engineer enters the command 'ip pim rp-address 10.1.1.1' but multicast traffic is not being forwarded. Upon verification, the engineer sees that the RP is reachable via OSPF, but the 'show ip pim rp mapping' command does not list any RP for the group. What is the most likely cause?

Trap 1: The RP address is not reachable via the unicast routing table.

Incorrect because the scenario states the RP is reachable via OSPF.

Trap 2: PIM sparse mode must be enabled on all interfaces first.

Incorrect because PIM can be enabled per interface, but the RP mapping command is global and does not require all interfaces to have PIM enabled.

Trap 3: The router must be configured as a candidate RP using 'ip pim…

Incorrect because that command is used for Auto-RP or BSR, not for static RP configuration.

Study all IP Multicast common traps →

A
The RP address is not reachable via the unicast routing table.
Why wrong: Incorrect because the scenario states the RP is reachable via OSPF.
B
The command 'ip pim rp-address 10.1.1.1' must include an access-list to define the group range.
Correct because the RP mapping requires an access-list to specify the groups; without it, the RP is not associated with any group.
C
PIM sparse mode must be enabled on all interfaces first.
Why wrong: Incorrect because PIM can be enabled per interface, but the RP mapping command is global and does not require all interfaces to have PIM enabled.
D
The router must be configured as a candidate RP using 'ip pim send-rp-announce'.
Why wrong: Incorrect because that command is used for Auto-RP or BSR, not for static RP configuration.

Full breakdown with real-world context →

Question 4hardmultiple choice

Study the full multicast explanation →

A network engineer is troubleshooting multicast connectivity in a large enterprise. The network uses PIM sparse mode with Auto-RP. The engineer notices that some routers are not receiving the RP mapping for a particular group. The engineer checks the Auto-RP mapping agent and sees that it is sending RP announcements, but the routers that are missing the mapping are not in the same PIM domain. What is the most likely reason?

Trap 1: The mapping agent is not configured as a candidate RP.

Incorrect because the mapping agent only needs to receive RP announcements, not be a candidate itself.

Trap 2: The TTL of the RP announcements is set too low.

Incorrect because Auto-RP announcements are sent with a default TTL of 32, which is usually sufficient.

Trap 3: The routers missing the mapping have PIM dense mode enabled.

Incorrect because PIM dense mode does not prevent Auto-RP processing; the issue is specific to listening to the Auto-RP groups.

Study all IP Multicast common traps →

A
The routers missing the mapping do not have 'ip pim autorp listener' configured.
Correct because Auto-RP uses reserved multicast groups; without this command, routers may not process the RP announcements.
B
The mapping agent is not configured as a candidate RP.
Why wrong: Incorrect because the mapping agent only needs to receive RP announcements, not be a candidate itself.
C
The TTL of the RP announcements is set too low.
Why wrong: Incorrect because Auto-RP announcements are sent with a default TTL of 32, which is usually sufficient.
D
The routers missing the mapping have PIM dense mode enabled.
Why wrong: Incorrect because PIM dense mode does not prevent Auto-RP processing; the issue is specific to listening to the Auto-RP groups.

Full breakdown with real-world context →

Question 5mediummultiple choice

Open the full VLAN trunking answer →

An engineer is configuring multicast on a Cisco switch running IOS. The switch is acting as the IGMP querier for a VLAN. The engineer notices that multicast traffic is being flooded to all ports in the VLAN, even though only a few receivers have joined the group. The engineer checks the IGMP snooping configuration and sees that IGMP snooping is enabled globally and on the VLAN. What is the most likely cause of the flooding?

Trap 1: The multicast source is connected to a trunk port.

Incorrect because the source port type does not directly cause flooding; IGMP snooping works on trunk ports as well.

Trap 2: The switch has PIM enabled on the VLAN interface.

Incorrect because PIM is for Layer 3 multicast routing, not for Layer 2 IGMP snooping.

Trap 3: The receivers are using IGMPv3.

Incorrect because IGMPv3 is supported by IGMP snooping and does not cause flooding.

Study all IP Multicast common traps →

A
The IGMP querier is not elected on the VLAN.
Correct because without a querier, IGMP snooping cannot learn group memberships, causing the switch to flood multicast traffic.
B
The multicast source is connected to a trunk port.
Why wrong: Incorrect because the source port type does not directly cause flooding; IGMP snooping works on trunk ports as well.
C
The switch has PIM enabled on the VLAN interface.
Why wrong: Incorrect because PIM is for Layer 3 multicast routing, not for Layer 2 IGMP snooping.
D
The receivers are using IGMPv3.
Why wrong: Incorrect because IGMPv3 is supported by IGMP snooping and does not cause flooding.

Full breakdown with real-world context →

Question 6hardmultiple choice

Study the full multicast explanation →

A network engineer is configuring PIM sparse mode in a network that uses a Bootstrap Router (BSR) for RP discovery. The engineer has configured a candidate BSR and candidate RPs. However, some routers in the network are not learning the RP set. The engineer checks the BSR and sees that it is receiving candidate RP advertisements, but the BSR messages are not being forwarded to all routers. What is the most likely cause?

Trap 1: The candidate BSR priority is set too low.

Incorrect because priority affects BSR election, not the flooding of BSR messages.

Trap 2: The candidate RPs are not in the same OSPF area as the BSR.

Incorrect because BSR messages are flooded regardless of OSPF areas, as long as PIM is enabled.

Trap 3: The BSR is not configured as a candidate RP.

Incorrect because the BSR does not need to be an RP; its role is to distribute RP information.

Study all IP Multicast common traps →

A
PIM is not enabled on all interfaces between the BSR and the other routers.
Correct because BSR messages rely on PIM to flood; without PIM on intermediate interfaces, the messages are dropped.
B
The candidate BSR priority is set too low.
Why wrong: Incorrect because priority affects BSR election, not the flooding of BSR messages.
C
The candidate RPs are not in the same OSPF area as the BSR.
Why wrong: Incorrect because BSR messages are flooded regardless of OSPF areas, as long as PIM is enabled.
D
The BSR is not configured as a candidate RP.
Why wrong: Incorrect because the BSR does not need to be an RP; its role is to distribute RP information.

Full breakdown with real-world context →

Question 7mediummultiple choice

Study the full multicast explanation →

An engineer is troubleshooting multicast performance issues. The network uses PIM sparse mode with a static RP. The engineer notices that the multicast traffic from a source to a group is taking a suboptimal path, causing high latency. The engineer checks the multicast routing table on the last-hop router and sees that the (S,G) entry has an incoming interface that is not the shortest path to the source. What is the most likely reason for this suboptimal path?

Trap 1: The RP is not configured as the DR on its segment.

Incorrect because the DR role is for the source segment, not for path selection.

Trap 2: The multicast source is using a different group address.

Incorrect because the group address is consistent; the path issue is related to tree type.

Trap 3: The last-hop router has a higher metric to the source than to the…

Incorrect because even if the metric is higher, the SPT switchover would use the source path; the issue is that the switchover hasn't occurred.

Study all IP Multicast common traps →

A
The last-hop router has not yet switched to the SPT.
Correct because the default behavior is to switch to the SPT after the first packet, but if disabled or delayed, the shared tree is used.
B
The RP is not configured as the DR on its segment.
Why wrong: Incorrect because the DR role is for the source segment, not for path selection.
C
The multicast source is using a different group address.
Why wrong: Incorrect because the group address is consistent; the path issue is related to tree type.
D
The last-hop router has a higher metric to the source than to the RP.
Why wrong: Incorrect because even if the metric is higher, the SPT switchover would use the source path; the issue is that the switchover hasn't occurred.

Full breakdown with real-world context →

Question 8easymultiple choice

Study the full multicast explanation →

A network engineer is configuring multicast on a Cisco router that connects to a multi-access network. The engineer wants to ensure that only one router forwards multicast traffic onto the segment to avoid duplication. The engineer enables PIM on the interface. However, multicast traffic is still being duplicated on the segment. What is the most likely reason?

Trap 1: The interface is configured as a passive interface under OSPF.

Incorrect because OSPF passive interface does not affect PIM DR election.

Trap 2: IGMP snooping is disabled on the switch connecting the routers.

Incorrect because IGMP snooping is a Layer 2 feature and does not affect PIM DR behavior.

Trap 3: The multicast group is in the 224.0.0.0/24 range.

Incorrect because the group range does not affect DR election; DR election is per interface.

Study all IP Multicast common traps →

A
Both routers have the same DR priority and the DR election has not completed.
Correct because if the DR priority is equal, the router with the higher IP address becomes DR; if not elected, both may forward.
B
The interface is configured as a passive interface under OSPF.
Why wrong: Incorrect because OSPF passive interface does not affect PIM DR election.
C
IGMP snooping is disabled on the switch connecting the routers.
Why wrong: Incorrect because IGMP snooping is a Layer 2 feature and does not affect PIM DR behavior.
D
The multicast group is in the 224.0.0.0/24 range.
Why wrong: Incorrect because the group range does not affect DR election; DR election is per interface.

Full breakdown with real-world context →

Question 9easymultiple choice

Study the full multicast explanation →

An engineer is configuring multicast on a Cisco router. The router receives multicast traffic from a source on interface GigabitEthernet0/0 and needs to forward it to receivers on interface GigabitEthernet0/1. The engineer enables PIM sparse mode on both interfaces and configures a static RP. However, the router does not create a multicast routing entry for the (S,G) pair. What is the most likely missing configuration?

Trap 1: The interface GigabitEthernet0/0 is not configured with an IP…

Incorrect because the interface must have an IP address, but the scenario implies it is receiving traffic, so it likely has an IP.

Trap 2: The RP address is not reachable from the router.

Incorrect because the RP is needed for group-to-RP mapping, but the (S,G) entry should still be created if the source is directly connected.

Trap 3: The router is not configured as a candidate RP.

Incorrect because the router does not need to be an RP to forward multicast traffic.

Study all IP Multicast common traps →

A
The global command 'ip multicast-routing' is not configured.
Correct because this command is required to enable multicast routing on the router.
B
The interface GigabitEthernet0/0 is not configured with an IP address.
Why wrong: Incorrect because the interface must have an IP address, but the scenario implies it is receiving traffic, so it likely has an IP.
C
The RP address is not reachable from the router.
Why wrong: Incorrect because the RP is needed for group-to-RP mapping, but the (S,G) entry should still be created if the source is directly connected.
D
The router is not configured as a candidate RP.
Why wrong: Incorrect because the router does not need to be an RP to forward multicast traffic.

Full breakdown with real-world context →

Question 10mediummultiple choice

Study the full multicast explanation →

A network engineer runs the following command on Router R1:

R1# show ip pim neighbor

PIM Neighbor Table

Neighbor Address  Interface           Uptime    Expires   Mode
10.1.1.2          GigabitEthernet0/0  2w0d      00:01:25  DR
10.1.1.3          GigabitEthernet0/0  2w0d      00:01:20  B

Based on this output, what can be concluded?

Trap 1: PIM sparse mode is operating on this interface.

In sparse mode, the DR flag would be present, but the B flag indicates Bidir.

Trap 2: PIM dense mode is in use on this interface.

Dense mode does not use DR election or show B flag.

Trap 3: PIM SSM is enabled on this interface.

SSM does not use DR election; it relies on IGMPv3.

Study all IP Multicast common traps →

A
PIM sparse mode is operating on this interface.
Why wrong: In sparse mode, the DR flag would be present, but the B flag indicates Bidir.
B
PIM Bidir mode is configured on this interface.
The B flag in the Mode column indicates Bidir capability, and the DR flag is also present, which is consistent with Bidir operation.
C
PIM dense mode is in use on this interface.
Why wrong: Dense mode does not use DR election or show B flag.
D
PIM SSM is enabled on this interface.
Why wrong: SSM does not use DR election; it relies on IGMPv3.

Full breakdown with real-world context →

Question 11mediummultiple choice

Study the full multicast explanation →

A network engineer issues the following command on Router R2:

R2# show ip mroute 239.1.1.1
IP Multicast Routing Table

Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group session, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.1.1.1), 00:03:45/00:02:15, RP 10.0.0.1, flags: S Incoming interface: GigabitEthernet0/0, RPF nbr 10.0.0.1 Outgoing interface list: GigabitEthernet0/1, Forward/Sparse, 00:03:45/00:02:15

Based on this output, what can be concluded?

Trap 1: The group is using PIM dense mode.

The flags show 'S' for sparse, not 'D' for dense.

Trap 2: The multicast traffic is being hardware switched.

There is no 'H' flag in the outgoing interface flags.

Trap 3: The group is a Bidir group.

The flags show 'S' for sparse, not 'B' for Bidir.

Study all IP Multicast common traps →

A
The group is using PIM dense mode.
Why wrong: The flags show 'S' for sparse, not 'D' for dense.
B
The RP for this group is 10.0.0.1.
The output clearly states 'RP 10.0.0.1' in the (*,G) entry.
C
The multicast traffic is being hardware switched.
Why wrong: There is no 'H' flag in the outgoing interface flags.
D
The group is a Bidir group.
Why wrong: The flags show 'S' for sparse, not 'B' for Bidir.

Full breakdown with real-world context →

Question 12mediummultiple choice

Study the full multicast explanation →

A network engineer executes the following command on Router R3:

R3# show ip igmp groups 239.2.2.2

IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter

239.2.2.2        GigabitEthernet0/0       1d04h     00:02:10  192.168.1.100

Based on this output, what can be concluded?

Trap 1: The multicast group is being sourced from 192.168.1.100.

The last reporter is the host that last sent an IGMP report, not necessarily the source.

Trap 2: The router is the RP for this group.

The output does not show RP information.

Trap 3: The group is using IGMP version 3.

The output does not indicate IGMP version; it only shows group membership.

Study all IP Multicast common traps →

A
The multicast group is being sourced from 192.168.1.100.
Why wrong: The last reporter is the host that last sent an IGMP report, not necessarily the source.
B
A host at 192.168.1.100 has joined group 239.2.2.2.
The last reporter indicates the host that sent the most recent IGMP membership report for this group.
C
The router is the RP for this group.
Why wrong: The output does not show RP information.
D
The group is using IGMP version 3.
Why wrong: The output does not indicate IGMP version; it only shows group membership.

Full breakdown with real-world context →

Question 13hardmultiple choice

Study the full multicast explanation →

A network engineer runs the following command on Router R4:

R4# show ip pim rp mapping

PIM Group-to-RP Mappings This system is an RP (Auto-RP) This system is an RP (BSR) Group(s) 224.0.0.0/4 RP 10.0.0.2 (?), v2v1 Info source: 10.0.0.2 (?), elected via Auto-RP, expires in 00:01:30 RP 10.0.0.3 (?), v2v1 Info source: 10.0.0.3 (?), elected via BSR, expires in 00:02:00

Based on this output, what can be concluded?

Trap 1: Only Auto-RP is being used for RP mapping.

BSR is also present as indicated by the 'elected via BSR' line.

Trap 2: Only BSR is being used for RP mapping.

Auto-RP is also present as indicated by the 'elected via Auto-RP' line.

Trap 3: The router is not an RP.

The output explicitly states 'This system is an RP' for both Auto-RP and BSR.

Study all IP Multicast common traps →

A
Only Auto-RP is being used for RP mapping.
Why wrong: BSR is also present as indicated by the 'elected via BSR' line.
B
Only BSR is being used for RP mapping.
Why wrong: Auto-RP is also present as indicated by the 'elected via Auto-RP' line.
C
Both Auto-RP and BSR are configured, causing multiple RP mappings.
The output shows two different RPs for the same group range, learned from different protocols.
D
The router is not an RP.
Why wrong: The output explicitly states 'This system is an RP' for both Auto-RP and BSR.

Full breakdown with real-world context →

Question 14mediummultiple choice

Study the full multicast explanation →

A network engineer issues the following command on Router R5:

R5# show ip pim interface
Interface          PIM  Nbrs  Hello  DR    DR

Count Intvl Prior GigabitEthernet0/0 on 2 30 1 10.1.1.1 GigabitEthernet0/1 on 1 30 1 10.2.2.2 Loopback0 on 0 30 1 10.3.3.3

Based on this output, what can be concluded?

Trap 1: The DR on GigabitEthernet0/1 is the local router.

The DR is 10.2.2.2, which may or may not be the local router; the output does not indicate the local router's IP.

Trap 2: PIM is disabled on Loopback0.

The interface shows 'on', meaning PIM is enabled.

Trap 3: The hello interval on GigabitEthernet0/0 is 60 seconds.

The hello interval is 30 seconds as shown.

Study all IP Multicast common traps →

A
The DR on GigabitEthernet0/0 is 10.1.1.1.
The DR column shows 10.1.1.1 for that interface.
B
The DR on GigabitEthernet0/1 is the local router.
Why wrong: The DR is 10.2.2.2, which may or may not be the local router; the output does not indicate the local router's IP.
C
PIM is disabled on Loopback0.
Why wrong: The interface shows 'on', meaning PIM is enabled.
D
The hello interval on GigabitEthernet0/0 is 60 seconds.
Why wrong: The hello interval is 30 seconds as shown.

Full breakdown with real-world context →

Question 15mediummultiple choice

Study the full multicast explanation →

A network engineer runs the following command on Router R6:

R6# show ip pim rp 239.3.3.3

RP 10.0.0.4

Info source: 10.0.0.4, via bootstrap, priority 192, holdtime 150, expires in 00:02:30

Based on this output, what can be concluded?

Trap 1: The RP was learned via Auto-RP.

The output says 'via bootstrap', which is BSR.

Trap 2: The RP was statically configured.

Static configuration would not show 'via bootstrap'.

Trap 3: The RP is 10.0.0.5.

The output shows RP 10.0.0.4.

Study all IP Multicast common traps →

A
The RP was learned via Auto-RP.
Why wrong: The output says 'via bootstrap', which is BSR.
B
The RP was learned via BSR.
The output explicitly states 'via bootstrap'.
C
The RP was statically configured.
Why wrong: Static configuration would not show 'via bootstrap'.
D
The RP is 10.0.0.5.
Why wrong: The output shows RP 10.0.0.4.

Full breakdown with real-world context →

Question 16hardmultiple choice

Study the full multicast explanation →

A network engineer issues the following command on Router R7:

R7# show ip pim tunnel

Tunnel1: Type: PIM Encap Source: 10.0.0.7, Destination: 10.0.0.8 Status: up

Based on this output, what can be concluded?

Trap 1: This tunnel is used for MDT data group forwarding.

MDT tunnels are used in MVPN, not for PIM register.

Trap 2: This tunnel is used for BSR messages.

BSR messages are not encapsulated in tunnels.

Trap 3: This tunnel is used for Auto-RP announcements.

Auto-RP uses multicast, not tunnels.

Study all IP Multicast common traps →

A
This tunnel is used for PIM register encapsulation to the RP.
PIM Encap tunnels are used to encapsulate multicast packets from the first-hop router to the RP.
B
This tunnel is used for MDT data group forwarding.
Why wrong: MDT tunnels are used in MVPN, not for PIM register.
C
This tunnel is used for BSR messages.
Why wrong: BSR messages are not encapsulated in tunnels.
D
This tunnel is used for Auto-RP announcements.
Why wrong: Auto-RP uses multicast, not tunnels.

Full breakdown with real-world context →

Question 17mediummultiple choice

Study the full multicast explanation →

A network engineer runs the following command on Router R8:

R8# show ip mroute count
IP Multicast Statistics

Group: 239.4.4.4, Source: 10.0.0.9 Packets: 1500, Bytes: 1200000, Average rate: 8000 pps, 5 sec rate: 0 pps

Group: 239.5.5.5, Source: 10.0.0.10 Packets: 0, Bytes: 0, Average rate: 0 pps, 5 sec rate: 0 pps

Based on this output, what can be concluded?

Trap 1: Multicast traffic is flowing for group 239.5.5.5.

The counts are zero, indicating no traffic.

Trap 2: Both groups are receiving traffic.

Only one group has non-zero counts.

Trap 3: The source for group 239.4.4.4 is 10.0.0.10.

The source is 10.0.0.9, not 10.0.0.10.

Study all IP Multicast common traps →

A
Multicast traffic is flowing for group 239.4.4.4.
The packet and byte counts are non-zero, indicating traffic.
B
Multicast traffic is flowing for group 239.5.5.5.
Why wrong: The counts are zero, indicating no traffic.
C
Both groups are receiving traffic.
Why wrong: Only one group has non-zero counts.
D
The source for group 239.4.4.4 is 10.0.0.10.
Why wrong: The source is 10.0.0.9, not 10.0.0.10.

Full breakdown with real-world context →

Question 18hardmultiple choice

Study the full multicast explanation →

A network engineer issues the following command on Router R9:

R9# show ip pim bsr-router

PIMv2 Bootstrap Router (BSR) information This system is the Bootstrap Router (BSR) BSR address: 10.0.0.11 Uptime: 1w2d, BSR priority: 0, Hash mask length: 30 Next bootstrap message in 00:00:45

Based on this output, what can be concluded?

Trap 1: This router is a candidate BSR but not elected.

It explicitly says it is the BSR.

Trap 2: The BSR priority is 192.

The priority is 0.

Trap 3: The hash mask length is 32.

The hash mask length is 30.

Study all IP Multicast common traps →

A
This router is the elected BSR.
The output states 'This system is the Bootstrap Router'.
B
This router is a candidate BSR but not elected.
Why wrong: It explicitly says it is the BSR.
C
The BSR priority is 192.
Why wrong: The priority is 0.
D
The hash mask length is 32.
Why wrong: The hash mask length is 30.

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Question 19mediummultiple choice

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Consider the following configuration snippet on a Cisco IOS-XE router:

interface GigabitEthernet0/1
 ip address 10.1.1.1 255.255.255.0
 ip pim sparse-mode
 ip igmp version 3

router ospf 1
 network 10.1.1.0 0.0.0.255 area 0

What is the effect of this configuration?

Trap 1: The interface will operate in PIM dense-mode because no RP is…

Incorrect. PIM sparse-mode is explicitly configured; without an RP, the router will not forward multicast traffic correctly, but it does not fall back to dense-mode.

Trap 2: IGMPv3 is incompatible with PIM sparse-mode and will be ignored.

Incorrect. IGMPv3 works with PIM sparse-mode and is actually required for SSM.

Trap 3: The router will automatically use dense-mode because OSPF is…

Incorrect. OSPF is a unicast routing protocol and does not affect PIM mode selection.

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A
The interface will participate in PIM sparse-mode and IGMPv3, but PIM sparse-mode requires an RP to be configured or learned.
Correct. PIM sparse-mode requires an RP. IGMPv3 is supported but the RP must be defined for sparse-mode to work.
B
The interface will operate in PIM dense-mode because no RP is configured.
Why wrong: Incorrect. PIM sparse-mode is explicitly configured; without an RP, the router will not forward multicast traffic correctly, but it does not fall back to dense-mode.
C
IGMPv3 is incompatible with PIM sparse-mode and will be ignored.
Why wrong: Incorrect. IGMPv3 works with PIM sparse-mode and is actually required for SSM.
D
The router will automatically use dense-mode because OSPF is enabled.
Why wrong: Incorrect. OSPF is a unicast routing protocol and does not affect PIM mode selection.

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Question 20mediummultiple choice

Study the full multicast explanation →

Examine the following configuration on a Cisco IOS-XE router:

ip multicast-routing distributed

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 ip pim sparse-dense-mode
 ip igmp version 2

Which statement about this configuration is true?

Trap 1: The interface will operate in dense-mode for all multicast groups…

Incorrect. Sparse-dense-mode allows the interface to use dense-mode only for groups that do not have an RP, but it will attempt to use sparse-mode if an RP is known.

Trap 2: The router will only support IGMPv2, and IGMPv3 queries will be…

Incorrect. The router can still process IGMPv3 reports if received, but it will send IGMPv2 queries. IGMPv3 is not explicitly enabled.

Trap 3: The configuration is invalid because 'ip multicast-routing…

Incorrect. 'ip multicast-routing distributed' is a valid command on many Cisco IOS-XE platforms to enable multicast routing with distributed switching.

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A
The interface will operate in dense-mode for all multicast groups because no RP is configured.
Why wrong: Incorrect. Sparse-dense-mode allows the interface to use dense-mode only for groups that do not have an RP, but it will attempt to use sparse-mode if an RP is known.
B
The router will only support IGMPv2, and IGMPv3 queries will be ignored.
Why wrong: Incorrect. The router can still process IGMPv3 reports if received, but it will send IGMPv2 queries. IGMPv3 is not explicitly enabled.
C
Multicast routing is enabled with distributed switching, and the interface will use sparse-mode if an RP is known for the group, otherwise dense-mode.
Correct. The 'ip multicast-routing distributed' enables multicast routing with CEF-based distributed switching. Sparse-dense-mode adapts based on RP knowledge.
D
The configuration is invalid because 'ip multicast-routing distributed' is not a valid command.
Why wrong: Incorrect. 'ip multicast-routing distributed' is a valid command on many Cisco IOS-XE platforms to enable multicast routing with distributed switching.

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What does the 350-401 exam test about IP Multicast?: IP Multicast questions test whether you can apply the concept in context, not just recognise a definition.
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