Question 1mediummatching
Study the full multicast explanation →Question 977 of 2,015
Quick Answer
The answer is that PIM Sparse-Dense Mode allows an interface to operate in either sparse or dense mode on a per-group basis, making it the correct match for that description. This flexibility is necessary because PIM Sparse Mode relies on explicit join messages to build a shared tree before optionally switching to a shortest-path tree, while PIM Dense Mode uses a flood-and-prune approach. PIM SSM exclusively builds source-specific trees, and PIM Bidir uses a single shared tree with a designated forwarder to prevent loops, never switching to a source-specific tree. On the ENCOR 350-401 exam, this drag-and-drop task tests your ability to distinguish each mode’s fundamental traffic distribution method, with a common trap being confusion over Sparse-Dense Mode’s per-group adaptability versus a static mode. Remember the key: Sparse = explicit join, Dense = flood and prune, SSM = source-only tree, Bidir = shared tree only.
350-401 IP Multicast Practice Question
This 350-401 practice question tests your understanding of ip multicast. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Drag and drop each PIM mode on the left to its matching traffic distribution method on the right.
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
✓
PIM Sparse Mode (SM): Uses explicit join messages to build a shared tree, then can switch to shortest-path tree
PIM Sparse Mode uses explicit join to build shared tree then optionally switch to SPT; PIM Dense Mode floods and prunes; PIM SSM uses exclusively source-specific trees; PIM Bidir uses a shared tree with no source-specific tree and a designated forwarder to prevent loops.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this 350-401 question test?
IP Multicast — This question tests IP Multicast — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: PIM Sparse Mode (SM): Uses explicit join messages to build a shared tree, then can switch to shortest-path tree — PIM Sparse Mode uses explicit join to build shared tree then optionally switch to SPT; PIM Dense Mode floods and prunes; PIM SSM uses exclusively source-specific trees; PIM Bidir uses a shared tree with no source-specific tree and a designated forwarder to prevent loops.
What should I do if I get this 350-401 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Same concept, more angles
1 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Drag and drop each PIM mode on the left to its matching traffic distribution method on the right.
medium- ✓ P1.PIM Sparse Mode: Uses explicit join messages to build a shared tree
- ✓ P2.PIM Dense Mode: Floods multicast traffic on all interfaces, then prunes unwanted branches
- ✓ P3.PIM Source-Specific Mode: Builds shortest path trees from source to receivers
- ✓ P4.PIM Bidirectional Mode: Uses a shared tree with no source-specific state
- ✓ P5.PIM Sparse-Dense Mode: Operates in sparse mode by default, but allows dense mode per group
Why P1: PIM Sparse Mode uses explicit join to build a shared tree; Dense Mode floods initially then prunes; Source-Specific Mode uses shortest path trees from source; Bidirectional PIM uses a shared tree with no source-specific state.
Last reviewed: Jun 18, 2026
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