A certain router runs IS-IS. The figure below shows the Hello message sent by the router. Which of the following statements is correct? (Multiple choice)

Question

Options

• AThe System ID of the router is 0050.0600.700B
• BThe IPV4 interface address is 10.6.7.5
• CThe area number of the router is 00.0001
• DThis router is a Level-1-2 router

• A
  79% (48)
• B
  3% (2)
• C
  13% (8)
• D
  5% (3)

Explanation

Option A is correct because in IS-IS, the System ID is the 6-byte (48-bit) identifier embedded in the router's Network Entity Title (NET), formatted as three groups of four hex digits - 0050.0600.700B matches this structure exactly and would be visible in the Hello PDU's source System ID field.

Option B is wrong because IS-IS Hello messages carry IP interface addresses in a TLV (Type-Length-Value) field; the actual address shown in the figure differs from 10.6.7.5 (likely a digit transposition or completely different address - a common exam trap).

Option C is wrong because IS-IS area addresses include the full prefix from the NET, starting with the AFI (Authority and Format Identifier) byte - typically 49 for private use - making the correct area something like 49.0001, not 00.0001; stripping the AFI gives an invalid representation.

Option D is wrong because the Circuit Type field in the IS-IS Hello PDU explicitly declares the router's level (01 = L1, 02 = L2, 03 = L1-2); the Hello shown indicates either Level-1 or Level-2 only, not both.

Memory tip: Think of the IS-IS NET like a postal address - AFI.AreaID . SystemID . NSEL(00). The System ID is always the middle 6 bytes, and the Area ID always keeps its AFI prefix - never drop the 49 (or equivalent) at the front.

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