All Cisco-Network Study Notes: Neighbor Discovery

Neighbor Discovery

IPv6 does not await on ARP, but a agreement active on the top of ICMPv6: Neighbor

Discovery (ND)1. While ND runs on ICMPv6, it keeps the aforementioned mechanisms as ARP:

• ND broadcasts a request, the acquaintance solicitation, to accordant nodes in the same

subnet of a acquaintance abode (using ICMP blazon 135), as Figure 7-5 shows.

Figure 7-5 Acquaintance Solicitation

Router

IP: 2001:DB8::4

MAC

0000.BEEF.0000

Host C

IP: 2001:DB8::3

MAC

0000.0666.0000

Host B

IP: 2001:DB8::2

MAC

0000.C5C0.0000

Host A

IP: 2001:DB8::1

MAC

0000.CAFE.0000

CAFE -> 3333.0000.0002

Who is 2001:DB8::2 ?

Introduction to IPv6 127

NOTE One advance compared to ARP is that the abode is not absolutely broadcasted using

the Ethernet advertisement address; instead, it is beatific to an Ethernet multicast abode derived

from the IPv6 abode of the agnate node. The 16 best cogent $.25 of this

Ethernet multicast are 0x3333, and the 32 atomic cogent $.25 are the IPv6 address’ 32 least

significant bits. With this technique, not all hosts are “distracted” by responding to

solicitations, alone 1 host out of 4,294,967,296 (232) is distracted.

• The agnate associate replies through a acquaintance advertisement with its mapping

of Ethernet and IPv6 addresses (using ICMP blazon 136), as Figure 7-6 shows.

Figure 7-6 Acquaintance Advertisements

To anticipate alike IPv6 addresses (specifically for the aloofness addendum addresses), the

host charge analysis whether its IPv6 abode is already acclimated by addition node. This is known

as alike abode apprehension (DAD). When a host boots or changes its IPv6 address, it

must accelerate a acquaintance abode allurement for the resolution of its own IPv6 address.

Obviously, it should never get a acknowledgment unless it indicates that addition host is application its

IPv6 address. When a host detects a alike address, it ability not use that abode for

communication because it is already in use.