350-501 Architecture Practice Question
In IS-IS, which TWO are types of Link State PDUs (LSPs)?
⚠ Common exam trap
Cisco often tests the distinction between PDU types (LSPs, CSNPs, PSNPs, and IIHs) and candidates mistakenly classify all IS-IS PDUs as LSPs, especially confusing CSNPs and PSNPs with actual Link State PDUs.
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
✓
Level 2 LSP
In IS-IS, Link State PDUs (LSPs) are the fundamental building blocks of the link-state database. They carry topology and prefix information and are generated by each router. There are two distinct types: Level 1 LSPs, which advertise information within the same area, and Level 2 LSPs, which advertise information between areas. Options B and E correctly identify these two types.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Partial Sequence Numbers PDU (PSNP)
Why it's wrong here
PSNP requests missing LSPs.
- ✓
Level 2 LSP
Why this is correct
Originated by Level 2 routers for inter-area reachability.
- ✗
Hello LSP
Why it's wrong here
Hello is a separate PDU type, not an LSP.
- ✗
Complete Sequence Numbers PDU (CSNP)
Why it's wrong here
CSNP is a different PDU type for database synchronization.
- ✓
Level 1 LSP
Why this is correct
Originated by Level 1 routers within the area.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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