Question

You have enabled IPv6 on two of your routers, but on the interfaces you have not assigned IPv6 addresses yet. You are surprised to learn that these two machines are exchanging information over those interfaces. How is this possible?a. Due to anycast addressingb. Due to ICMPv6c. Due to the NATv6 capabilityd. Due to the link-local IPv6 addresses

Answer 1

Answer:

You have enabled IPv6 on two of your routers, but on the interfaces you have not assigned IPv6 addresses yet. You are surprised to learn that these two machines are exchanging information over those interfaces. How is this possible?

a. Due to anycast addressing

b. Due to ICMPv6

c. Due to the NATv6 capability

d. Due to the link-local IPv6 addresses

The correct answer is D. Due to the link-local addresses

Explanation:

LINK-LOCAL ADDRESS

Link-local addresses are addresses that can be used for unicast communications on a confined LAN segment.  The requirement with these addresses is that they are only locally-significant (i.e., restricted to a single LAN broadcast domain) and are never used to source or receive communications across a layer-3 gateway.

Typically, link-local IPv6 addresses have “FE80” as the hexadecimal representation of the first 10 bits of the 128-bit IPv6 address, then the least-significant 64-bits of the address are the Interface Identifier (IID).  Depending on the IID algorithm the node’s operating system is using, the IID may use either modified EUI-64 with SLAAC, the privacy addressing method (RFC 4941)), or the newly published Stable SLAAC IID method(RFC 8064).

When a host boots up, it automatically assigns an FE80::/10 IPv6 address to its interface.  You can see the format of the link-local address below. It starts with FE80 and is followed by 54 bits of zeros. Lastly, the final 64-bits provide the unique Interface Identifier.

FE80:0000:0000:0000:abcd:abcd:abcd:abcd

Link-local IPv6 addresses are present on every interface of IPv6-enabled host and router.  They are vital for LAN-based Neighbor Discovery communication.  After the host has gone through the Duplicate Address Detection (DAD) process ensuring that its link-local address (and associated IID) is unique on the LAN segment, it then proceeds to sending an ICMPv6 Router Solicitation (RS) message sourced from that address.

IPv6 nodes send NS messages so that the link-layer address of a specific neighbor can be found. There are three operations in which this message is used:

▪   For detecting duplicate address

▪   Verification of neighbor reachability

▪   Layer 3 to Layer 2 address resolution (for ARP replacement)  ARP is not included in IPv6 as a protocol but rather the same functionality is integrated into ICMP as part of neighbor discovery. NA message is the response to an NS message.  From the figure the enabling of interaction or communication between neighbor discoveries between two IPv6 hosts can be clearly seen.