Question 1,918 of 2,015

IP Multicast →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the router will use 10.0.0.1 as the static RP for all multicast groups in the 224.0.0.0/8 range, with the interface operating in PIM sparse-mode. This static RP configuration ties the RP address directly to an access-list, so the router only considers 10.0.0.1 as the rendezvous point for groups matching ACL 10, which permits 224.0.0.0 through 224.255.255.255. On the ENCOR 350-401 exam, this tests your understanding of how static RP overrides dynamic RP discovery and that the RP must be unicast-reachable. A common trap is forgetting that 224.0.0.0/8 includes the reserved link-local range (224.0.0.0/24), which is not used with PIM, so the configuration is technically valid but suboptimal. Remember the memory tip: “Static RP ties groups to an ACL—match the range, but skip the link-local range.”

CCNP IP Multicast Practice Question

This 350-401 practice question tests your understanding of ip multicast. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Given the following partial configuration on a Cisco IOS-XE router:

ip pim rp-address 10.0.0.1 10
access-list 10 permit 224.0.0.0 0.255.255.255

interface GigabitEthernet0/0
 ip pim sparse-mode

What is the effect of this configuration?

Question 1mediummultiple choice

Study the full multicast explanation →

A
The router will use 10.0.0.1 as the RP for all multicast groups from 224.0.0.0 to 224.255.255.255, and the interface will operate in sparse-mode.
Correct. The static RP is defined for the group range specified in ACL 10, and the interface is in sparse-mode.
B
The router will ignore the static RP because the ACL includes the reserved link-local range (224.0.0.0/24).
Why wrong: Incorrect. The router will still use the static RP for all groups in the ACL, including the link-local range, though this is not recommended.
C
The interface must also be configured with 'ip pim dense-mode' for the RP to work.
Why wrong: Incorrect. PIM sparse-mode is required for RP-based multicast. Dense-mode does not use an RP.
D
The RP address 10.0.0.1 must be configured on a loopback interface on the same router.
Why wrong: Incorrect. The RP can be any reachable IP address, not necessarily on the same router.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The router will use 10.0.0.1 as the RP for all multicast groups from 224.0.0.0 to 224.255.255.255, and the interface will operate in sparse-mode.

This configures a static RP at 10.0.0.1 for multicast groups matching access-list 10, which permits all groups in the 224.0.0.0/8 range. The interface is in PIM sparse-mode. However, the RP address must be reachable via unicast routing. The configuration is valid but note that 224.0.0.0/8 includes reserved link-local addresses (224.0.0.0/24) which are not typically used with PIM.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
The router will use 10.0.0.1 as the RP for all multicast groups from 224.0.0.0 to 224.255.255.255, and the interface will operate in sparse-mode.
Why this is correct
Correct. The static RP is defined for the group range specified in ACL 10, and the interface is in sparse-mode.
Related concept
Standard ACLs match source addresses.
✗
The router will ignore the static RP because the ACL includes the reserved link-local range (224.0.0.0/24).
Why it's wrong here
Incorrect. The router will still use the static RP for all groups in the ACL, including the link-local range, though this is not recommended.
✗
The interface must also be configured with 'ip pim dense-mode' for the RP to work.
Why it's wrong here
Incorrect. PIM sparse-mode is required for RP-based multicast. Dense-mode does not use an RP.
✗
The RP address 10.0.0.1 must be configured on a loopback interface on the same router.
Why it's wrong here
Incorrect. The RP can be any reachable IP address, not necessarily on the same router.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 350-401 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 350-401 question test?

IP Multicast — This question tests IP Multicast — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The router will use 10.0.0.1 as the RP for all multicast groups from 224.0.0.0 to 224.255.255.255, and the interface will operate in sparse-mode. — This configures a static RP at 10.0.0.1 for multicast groups matching access-list 10, which permits all groups in the 224.0.0.0/8 range. The interface is in PIM sparse-mode. However, the RP address must be reachable via unicast routing. The configuration is valid but note that 224.0.0.0/8 includes reserved link-local addresses (224.0.0.0/24) which are not typically used with PIM.

What should I do if I get this 350-401 question wrong?

What is the key concept behind this question?

Standard ACLs match source addresses.

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