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Difficulty: Very hardIPv6 Addressing Concepts and Header Structure

A network security engineer is analyzing a packet capture containing IPv6 traffic in an enterprise network. The engineer notes two key requirements being evaluated:
1. An incoming IPv6 packet has a 20-bit header field set by the sending host so that intermediate routers can identify and maintain QoS forwarding for a specific real-time packet flow without inspecting transport layer headers.
2. A dual-stack host auto-configures its IPv6 interface address using EUI-64 SLAAC based on its physical MAC address of 00-15-5D-01-23-45.

Which option correctly identifies the 20-bit IPv6 header field used for flow identification AND the resulting EUI-64 Interface Identifier generated for this host?

  1. Flow Label header field; EUI-64 Interface Identifier is 0215:5dff:fe01:2345Answer
  2. B
    Traffic Class header field; EUI-64 Interface Identifier is 0015:5dff:fe01:2345
  3. C
    Flow Label header field; EUI-64 Interface Identifier is 0015:5dff:fe01:2345
  4. D
    Traffic Class header field; EUI-64 Interface Identifier is 0215:5dff:fe01:2345

Answer

The correct option states that the 20-bit header field is the Flow Label and the generated EUI-64 Interface Identifier is 0215:5dff:fe01:2345.
The 20-bit Flow Label field in the IPv6 base header is specifically designated for source hosts to tag sequences of packets belonging to a specific communication flow, enabling intermediate routers to perform QoS handling without inspecting transport-layer headers. For SLAAC address auto-configuration using Modified EUI-64 format, the 48-bit MAC address (00-15-5D-01-23-45) is split into two 24-bit halves, the 16-bit hex sequence FFFE is inserted in the middle (00-15-5D-FF-FE-01-23-45), and the 7th bit (Universal/Local bit) of the first byte is inverted (00000000 becomes 00000010, converting 00 to 02). Combining these yields the interface identifier 0215:5dff:fe01:2345.

Step-by-Step Solution

1
Identify the 20-bit IPv6 base header field designed for stream identification without transport layer parsing.
The 20-bit field is the Flow Label.
The IPv6 base header contains a 20-bit Flow Label field used to label sequences of packets belonging to a specific communication flow. (Traffic Class is an 8-bit field used for DSCP/CoS marking).
2
Split the 48-bit MAC address (00-15-5D-01-23-45) into two 24-bit halves and insert FFFE in the middle.
Inserting FFFE produces 00-15-5D-FF-FE-01-23-45.
Modified EUI-64 address generation requires expanding a 48-bit IEEE MAC address into a 64-bit interface identifier by inserting the 16-bit hexadecimal string FFFE.
3
Invert the 7th bit (Universal/Local bit) of the first byte.
The first byte 00 (00000000 in binary) becomes 02 (00000010 in binary).
IEEE EUI-64 formatting for IPv6 SLAAC requires inverting the 7th bit (the U/L bit) of the Organizationally Unique Identifier (OUI) to denote universal scope.
4
Format the resulting 64-bit sequence into IPv6 colon-hexadecimal notation.
Combining 02-15-5D-FF-FE-01-23-45 into 16-bit quads yields 0215:5dff:fe01:2345.
IPv6 addresses group 16-bit blocks separated by colons with leading zero suppression applied within each block.

Key Concept

IPv6 Base Header Field Functions (Flow Label vs. Traffic Class) and Modified EUI-64 Interface Identifier Generation Rules
Estimated Time:2m 0s
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Topics

IPv6 Addressing Concepts and Header Structure

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