350-401 IP Multicast — Timed 20 Questions

Question 1

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?

Accepted Answer

The multicast stream is arriving on an interface that is not the RPF interface for the source.. Multicast forwarding requires RPF check: the incoming interface for multicast traffic must match the unicast reverse path to the source. If the unicast route points to a different interface, the RPF check fails and the multicast packet is dropped, even if the DR is correct.

Answer

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

Answer

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

Answer

IGMP snooping is disabled on the receiver VLAN.

Question 2

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?

Accepted Answer

The RP is not configured on the last-hop router.. In PIM sparse mode, the last-hop router must send a PIM join toward the RP to join the shared tree. If the RP is reachable but the join is not being sent because the router does not know the RP or the group-to-RP mapping, the OIL remains empty.

Answer

The multicast source is not registered with the RP.

Answer

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

Answer

The TTL of the multicast packets is too low.

Question 3

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?

Accepted Answer

The command 'ip pim rp-address 10.1.1.1' must include an access-list to define the group range.. The 'ip pim rp-address' command requires an access-list to specify which groups the RP serves. Without the access-list, the command is incomplete and the RP mapping is not applied, even though the RP is reachable.

Answer

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

Answer

PIM sparse mode must be enabled on all interfaces first.

Answer

The router must be configured as a candidate RP using 'ip pim send-rp-announce'.

Question 4

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?

Accepted Answer

The routers missing the mapping do not have 'ip pim autorp listener' configured.. Auto-RP uses multicast groups 224.0.1.39 and 224.0.1.40. Routers must be configured to listen to these groups using the 'ip pim autorp listener' command, especially if they are not in the same PIM domain or if PIM is not enabled on all interfaces.

Answer

The mapping agent is not configured as a candidate RP.

Answer

The TTL of the RP announcements is set too low.

Answer

The routers missing the mapping have PIM dense mode enabled.

Question 5

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?

Accepted Answer

The IGMP querier is not elected on the VLAN.. IGMP snooping relies on the switch seeing IGMP membership reports. If the switch does not see the reports because the querier is not elected or because the reports are not forwarded to the switch CPU, the switch will flood multicast traffic to all ports.

Answer

The multicast source is connected to a trunk port.

Answer

The switch has PIM enabled on the VLAN interface.

Answer

The receivers are using IGMPv3.

Question 6

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?

Accepted Answer

PIM is not enabled on all interfaces between the BSR and the other routers.. BSR messages are flooded hop-by-hop using PIM. If PIM is not enabled on all interfaces between the BSR and the other routers, the BSR messages will not be forwarded, preventing RP discovery.

Answer

The candidate BSR priority is set too low.

Answer

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

Answer

The BSR is not configured as a candidate RP.

Question 7

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?

Accepted Answer

The last-hop router has not yet switched to the SPT.. In PIM sparse mode, the last-hop router initially joins the shared tree toward the RP. After receiving the first packet, it can optionally switch to the shortest path tree (SPT) by sending a join toward the source. If the SPT switchover is disabled or delayed, the traffic continues to use the shared tree, which may be suboptimal.

Answer

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

Answer

The multicast source is using a different group address.

Answer

The last-hop router has a higher metric to the source than to the RP.

Question 8

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?

Accepted Answer

Both routers have the same DR priority and the DR election has not completed.. On a multi-access network, PIM elects a Designated Router (DR) to forward multicast traffic. If the DR election fails or if both routers have the same DR priority, both may forward traffic, causing duplication.

Answer

The interface is configured as a passive interface under OSPF.

Answer

IGMP snooping is disabled on the switch connecting the routers.

Answer

The multicast group is in the 224.0.0.0/24 range.

Question 9

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?

Accepted Answer

The global command 'ip multicast-routing' is not configured.. For multicast routing to work, the 'ip multicast-routing' command must be enabled globally. Without it, the router will not create multicast forwarding entries, even if PIM is enabled on interfaces.

Answer

The interface GigabitEthernet0/0 is not configured with an IP address.

Answer

The RP address is not reachable from the router.

Answer

The router is not configured as a candidate RP.

Question 10

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?

Accepted Answer

PIM Bidir mode is configured on this interface.. The 'show ip pim neighbor' output shows two neighbors on the same interface. The 'Mode' column indicates the PIM neighbor role: 'DR' means Designated Router, 'B' means Bidir-capable. The presence of both DR and B on the same interface suggests that PIM Bidir mode is enabled, as Bidir uses a different DR election and the B flag indicates Bidir capability. The correct answer is that PIM Bidir is configured.

Answer

PIM sparse mode is operating on this interface.

Answer

PIM dense mode is in use on this interface.

Answer

PIM SSM is enabled on this interface.

Question 11

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?

Accepted Answer

The RP for this group is 10.0.0.1.. The 'show ip mroute' output shows a (*,G) entry for group 239.1.1.1 with flags 'S' (Sparse mode) and an RP of 10.0.0.1. The incoming interface is GigabitEthernet0/0 with RPF neighbor 10.0.0.1, and the outgoing interface list includes GigabitEthernet0/1 in Forward state. This indicates that the multicast route is using PIM sparse mode and the RP is known. The correct answer is that PIM sparse mode is used with an RP at 10.0.0.1.

Answer

The group is using PIM dense mode.

Answer

The multicast traffic is being hardware switched.

Answer

The group is a Bidir group.

Question 12

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?

Accepted Answer

A host at 192.168.1.100 has joined group 239.2.2.2.. The 'show ip igmp groups' output shows that group 239.2.2.2 is present on interface GigabitEthernet0/0, with the last reporter being 192.168.1.100. The uptime is 1 day and 4 hours, and the expiry timer is about 2 minutes. This indicates that there is at least one IGMP host on that subnet interested in the group. The correct answer is that a host at 192.168.1.100 has sent an IGMP report for this group.

Answer

The multicast group is being sourced from 192.168.1.100.

Answer

The router is the RP for this group.

Answer

The group is using IGMP version 3.

Question 13

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?

Accepted Answer

Both Auto-RP and BSR are configured, causing multiple RP mappings.. The output shows that this router is configured as an RP for both Auto-RP and BSR. There are two RPs for the same group range: one learned via Auto-RP (10.0.0.2) and one via BSR (10.0.0.3). The router itself is also an RP. This indicates that both Auto-RP and BSR are configured, which can cause conflicts. The correct answer is that both Auto-RP and BSR are active, leading to multiple RP mappings.

Answer

Only Auto-RP is being used for RP mapping.

Answer

Only BSR is being used for RP mapping.

Answer

The router is not an RP.

Question 14

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?

Accepted Answer

The DR on GigabitEthernet0/0 is 10.1.1.1.. The 'show ip pim interface' output shows that GigabitEthernet0/0 has 2 PIM neighbors, a hello interval of 30 seconds, DR priority of 1, and the DR is 10.1.1.1. GigabitEthernet0/1 has 1 neighbor and its DR is 10.2.2.2. Loopback0 has no neighbors and its DR is the router's own IP. The correct answer is that the DR on GigabitEthernet0/0 is 10.1.1.1, which is not the local router (since the local router's IP is not shown, but it is likely different).

Answer

The DR on GigabitEthernet0/1 is the local router.

Answer

PIM is disabled on Loopback0.

Answer

The hello interval on GigabitEthernet0/0 is 60 seconds.

Question 15

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?

Accepted Answer

The RP was learned via BSR.. The 'show ip pim rp' command shows the RP for group 239.3.3.3 is 10.0.0.4, learned via bootstrap (BSR). The priority is 192, holdtime 150 seconds, and it expires in 2 minutes 30 seconds. This indicates that BSR is the mechanism used to learn the RP. The correct answer is that the RP was learned via BSR.

Answer

The RP was learned via Auto-RP.

Answer

The RP was statically configured.

Answer

The RP is 10.0.0.5.

Question 16

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?

Accepted Answer

This tunnel is used for PIM register encapsulation to the RP.. The 'show ip pim tunnel' output shows a PIM encapsulation tunnel (Tunnel1) with source 10.0.0.7 and destination 10.0.0.8, and the status is up. This type of tunnel is used for PIM register encapsulation when a source sends to an RP. The correct answer is that this tunnel is used for sending register messages to the RP.

Answer

This tunnel is used for MDT data group forwarding.

Answer

This tunnel is used for BSR messages.

Answer

This tunnel is used for Auto-RP announcements.

Question 17

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?

Accepted Answer

Multicast traffic is flowing for group 239.4.4.4.. The 'show ip mroute count' output shows multicast statistics for two groups. For group 239.4.4.4, there are 1500 packets and 1200000 bytes, with an average rate of 8000 pps. For group 239.5.5.5, there are no packets. This indicates that multicast traffic is flowing for the first group but not for the second. The correct answer is that multicast traffic is being received for group 239.4.4.4.

Answer

Multicast traffic is flowing for group 239.5.5.5.

Answer

Both groups are receiving traffic.

Answer

The source for group 239.4.4.4 is 10.0.0.10.

Question 18

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?

Accepted Answer

This router is the elected BSR.. The 'show ip pim bsr-router' output shows that this router is the BSR with address 10.0.0.11, priority 0, and hash mask length 30. The next bootstrap message will be sent in 45 seconds. The hash mask length of 30 means that the group-to-RP mapping uses a 30-bit mask for hashing. The correct answer is that the BSR is elected and operational.

Answer

This router is a candidate BSR but not elected.

Answer

The BSR priority is 192.

Answer

The hash mask length is 32.

Question 19

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?

Accepted Answer

The interface will participate in PIM sparse-mode and IGMPv3, but PIM sparse-mode requires an RP to be configured or learned.. The interface is configured with PIM sparse-mode and IGMPv3. PIM sparse-mode requires a rendezvous point (RP) to be known, either statically or via Auto-RP/BSR. IGMPv3 allows source-specific multicast (SSM) with the SSM range (232.0.0.0/8). OSPF is enabled on the interface for unicast routing. The configuration is valid but missing an RP definition for sparse-mode to function correctly.

Answer

The interface will operate in PIM dense-mode because no RP is configured.

Answer

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

Answer

The router will automatically use dense-mode because OSPF is enabled.

Question 20

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?

Accepted Answer

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.. The 'ip multicast-routing distributed' command enables multicast routing with support for distributed switching (CEF). The interface is configured with PIM sparse-dense-mode, which allows the interface to operate in dense-mode if no RP is known for the group, or in sparse-mode if an RP is known. IGMPv2 is used for group membership.

Answer

The interface will operate in dense-mode for all multicast groups because no RP is configured.

Answer

The router will only support IGMPv2, and IGMPv3 queries will be ignored.

Answer

The configuration is invalid because 'ip multicast-routing distributed' is not a valid command.