A certain router runs IS-IS, and its output information is shown in the figure. Which of the following statements is correct?

Question

Options

• AThe cycle of sending IH on the S4/0/0 interface is 30s
• BThe circuit-level of the S4/0/0 interface is Level-1
• CThe IP Cost of the S4/0/0 interface is 20
• DThe S4/0/0 interface supports IPv6

• A
  7% (3)
• B
  74% (34)
• C
  17% (8)
• D
  2% (1)

Explanation

Option B is correct because the router's IS-IS output shows the S4/0/0 interface configured as a Level-1 circuit, meaning it only participates in intra-area routing and will exclusively form Level-1 adjacencies with neighbors in the same IS-IS area.

Why the distractors are wrong:

• A is wrong: The default IS-IS Hello (IH) interval is 10 seconds, not 30s. The figure would reflect this standard default, and 30s is not a typical IS-IS hello timer value.
• C is wrong: The default IS-IS interface IP cost is 10 (in narrow/legacy metric mode), not 20. Unless explicitly changed, interface costs default to 10 in most IS-IS implementations.
• D is wrong: The output shown would not indicate IPv6 capability for this interface; IS-IS IPv6 support requires explicit configuration (e.g., isis ipv6 enable), which would appear separately in the output.

Memory tip: Think of IS-IS levels like building floors - Level-1 = local floor (intra-area), Level-2 = between floors (inter-area). A Level-1-only interface never "leaves the floor," so if the output shows no Level-2 or L1/L2 designation, it's staying local. Also anchor the defaults: hello = 10s, cost = 10.

No community discussion yet for this question.