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Difficulty: MediumIPv6 Addressing Concepts and Header Structure

A network technician is performing a protocol analyzer capture to inspect traffic traversing an enterprise IPv6 router interface. Which of the following statements accurately describe the characteristics of IPv6 base headers and link-local addressing? (Select TWO.)

  1. The 8-bit Hop Limit field replaces the IPv4 Time to Live (TTL) field to prevent packets from circulating indefinitely in a routing loop.Answer
  2. Link-local addresses utilize the fe80::/10 prefix and are automatically configured for single-segment communication without being routed across subnets.Answer
  3. C
    An IPv6 link-local address can utilize double colons (::) multiple times in its shorthand notation if separated by non-zero hexadecimal fields.
  4. D
    The Next Header field is a 16-bit field dedicated exclusively to specifying Quality of Service (QoS) markings for voice traffic.

Answer

The correct statements are that the 8-bit Hop Limit field replaces the IPv4 Time to Live (TTL) field to prevent routing loops, and link-local addresses use the fe80::/10 prefix for single-segment, non-routable communication.
The Hop Limit field in the IPv6 base header serves as the direct replacement for IPv4's Time to Live (TTL) field, decrementing by one at each hop to eliminate packet loops. Furthermore, IPv6 link-local addresses fall under the fe80::/10 block (most commonly configured with fe80::/64) and are intended solely for local link communication, remaining non-routable across external networks.

Step-by-Step Solution

1
Analyze the Hop Limit field function in IPv6 headers.
Confirm that Hop Limit functions identically to IPv4 TTL, decrementing at each hop.
It prevents network packets from looping indefinitely on the network.
2
Evaluate link-local address prefixes and scope.
Identify fe80::/10 as the designated prefix scope for link-local traffic.
Link-local addresses are restricted to communication within the local broadcast/multicast domain and are discarded by routers.
3
Examine IPv6 shorthand address compression rules and Next Header functionality.
Reject invalid compression using multiple double colons and correct the field description of Next Header.
Using double colons more than once creates ambiguity, and Next Header identifies upper-layer protocols rather than QoS tags.

Key Concept

IPv6 Base Header Fields and Address Scope Characteristics
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Topics

IPv6 Addressing Concepts and Header Structure

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