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CCNA - IPv6 Fundamentals

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Question 1

The command `show ipv6 neighbors` on a Cisco router displays the IPv6 **neighbor cache**. What is the equivalent in IPv4?

Answer choices

  • A. `show ip arp` (Correct)

  • B. `show ip route`

  • C. `show ip interface`

  • D. `show ip nat translations`

Explanation

The IPv6 neighbor cache (displayed with `show ipv6 neighbors`) is the equivalent of the IPv4 ARP table (`show ip arp`). Both map Layer 3 addresses to Layer 2 MAC addresses for hosts on the same link. NDP/ICMPv6 populates the neighbor cache in IPv6, while ARP populates the ARP table in IPv4.

Question 2

Which **IPv6 transition mechanism** encapsulates IPv6 packets inside IPv4 packets to traverse IPv4-only infrastructure?

Answer choices

  • A. NAT64

  • B. Dual-stack

  • C. 6to4 tunneling (Correct)

  • D. ISATAP

Explanation

6to4 tunneling encapsulates IPv6 packets within IPv4 packets (protocol 41) to cross IPv4 networks. Dual-stack runs both IPv4 and IPv6 natively. NAT64 translates between IPv4 and IPv6. ISATAP is another tunneling mechanism for intra-site communication. Tunneling is not required when endpoints are dual-stack.

Question 3

IPv6 address compression allows consecutive groups of all zeros to be replaced with [[blank1]] (written once per address).

Explanation

The "::" (double colon) can replace one or more consecutive groups of all-zero hextets. For example, `2001:0db8:0000:0000:0000:0000:0000:0001` compresses to `2001:db8::1`. It can only be used once per address to avoid ambiguity.

Question 4

**True or False:** IPv6 header length is variable, similar to the IPv4 header, because it supports many optional fields.

Answer choices

  • A. True

  • B. False (Correct)

Explanation

The IPv6 base header is fixed at 40 bytes, which simplifies router processing and improves performance. Optional features are handled through extension headers that follow the main header. IPv4 headers vary from 20–60 bytes due to options.

Question 5

A router automatically generates a **link-local address** by combining FE80::/10 with an interface identifier derived from the MAC address using which process?

Answer choices

  • A. DHCP snooping

  • B. EUI-64 (Correct)

  • C. SLAAC prefix delegation

  • D. Stateful DHCPv6

Explanation

EUI-64 (Extended Unique Identifier) converts a 48-bit MAC address into a 64-bit interface identifier by inserting `FFFE` in the middle and flipping the 7th bit (universal/local bit). This 64-bit ID is appended to the /64 prefix to form a full 128-bit IPv6 address.