Basic IPv6 Functionality Protocols
IPv6 uses a cardinal of protocols to abutment it. Because IPv6 is fundamentally agnate to IPv4,
some of these protocols will be accustomed to you and are covered in added genitalia of this book—for
example, ICMP, CDP, and DHCP. However, some aspects of IPv6 operation, and absolutely some of
its greatest strengths, crave anatomic abutment from protocols not included in the IPv4 protocol
suite. Key amid them is Acquaintance Analysis Protocol, which provides abounding functions critical
in IPv6 networks. Added protocols, such as CDP, DNS, and ICMP, will be absolutely familiar.
Because acquaintance analysis is such a analytical action in IPv6 networks, this allotment of the chapter
starts with that and again moves on to the added accustomed protocols.
Neighbor Discovery
A above aberration amid IPv4 and IPv6 involves how IPv6 hosts apprentice their own addresses and
learn about their neighbors, including added hosts and routers. Acquaintance Analysis Protocol, also
Basic IPv6 Functionality Protocols 757
known as ND or NDP, facilitates this and added key functions. ND is authentic in RFC 2461. The
remainder of this area introduces ND functionality, lists its capital features, and again lists the
related ICMPv6 messages, which are above the ambit of the assay but are advantageous for abstraction and
reference.
In IPv6 networks, ND Agreement uses ICMPv6 letters and solicited-node multicast addresses for
its amount functions, which centermost on advertent and tracking added IPv6 hosts on connected
interfaces. ND is additionally acclimated for abode autoconfiguration.
Major roles of IPv6 ND accommodate the following:
■ Stateless abode autoconfiguration (detailed in RFC 2462)
■ Duplicate abode apprehension (DAD)
■ Router discovery
■ Prefix discovery
■ Parameter analysis (link MTU, hop limits)
■ Acquaintance discovery
■ Acquaintance abode resolution (replaces ARP, both activating and static)
■ Acquaintance and router reachability verification
ND uses bristles types of ICMPv6 letters to do its work. Table 20-4 defines those functions and
summarizes their goals.
Table 20-4 ND Functions in IPv6
Message
Type
Information Sought
or Sent Antecedent Abode Destination Address
ICMP
Type, Code
Router
Advertisement
(RA)
Routers acquaint their
presence and link
prefixes, MTU, and hop
limits.
Router’s link-local
address
FF02::1 for periodic
broadcasts; abode of
querying host for responses
to an RS
134, 0
Router
Solicitation
(RS)
Hosts concern for the
presence of routers on the
link.
Address assigned to
querying interface, if
assigned, or :: if not
assigned
FF02::2 133, 0
758 Chapter 20: IP Version 6
Neighbor Advertisements
IPv6 nodes accelerate Acquaintance Advertisement (NA) letters periodically to acquaint added hosts on the
same arrangement of their attendance and link-layer addresses.
Neighbor Solicitation
IPv6 nodes accelerate NS letters to acquisition the link-layer abode of a specific neighbor. This message
is acclimated in three operations:
■ Duplicate abode detection
■ Acquaintance reachability verification
■ Layer 3 to Layer 2 abode resolution (as a backup for ARP)
IPv6 does not accommodate ARP as a agreement but rather integrates the aforementioned functionality into ICMP as
part of acquaintance discovery. The acknowledgment to an NS bulletin is an NA message.
Figure 20-3 shows how acquaintance analysis enables advice amid two IPv6 hosts.
Message
Type
Information Sought
or Sent Antecedent Abode Destination Address
ICMP
Type, Code
Neighbor
Solicitation
(NS)
Hosts concern for other
nodes’ link-layer
addresses. Acclimated for
duplicate address
detection and to verify
neighbor reachability.
Address assigned to
querying interface, if
assigned, or :: if not
assigned
Solicited-node multicast
address or the ambition node’s
address, if known
135, 0
Neighbor
Advertisement
(NA)
Sent in acknowledgment to NS
messages and
periodically to provide
information to neighbors.
Configured or
automatically
assigned abode of
originating interface
Address of bulge requesting
the NA or FF02::1 for
periodic advertisements
136, 0
Redirect Sent by routers to inform
nodes of bigger next-hop
routers.
Link-local abode of
originating node
Source abode of
requesting node
137, 0
Table 20-4 ND Functions in IPv6 (Continued)
Basic IPv6 Functionality Protocols 759
Figure 20-3 Acquaintance Analysis Amid Two Hosts
Router Advertisement and Router Solicitation
A Cisco IPv6 router begins sending RA letters for anniversary of its configured interface prefixes
when the ipv6 unicast-routing command is configured. You can change the absence RA interval
(200 seconds) application the command ipv6 nd ra-interval. Router advertisements on a accustomed interface
include all of the 64-bit IPv6 prefixes configured on that interface. This allows for stateless address
autoconfiguration application EUI-64 to assignment properly. RAs additionally accommodate the articulation MTU, hop limits, and
whether a router is a applicant absence router.
IPv6 routers accelerate alternate RA letters to acquaint hosts about the IPv6 prefixes acclimated on the link
and to acquaint hosts that the router is accessible to be acclimated as a absence gateway. By default, a Cisco
router active IPv6 on an interface advertises itself as a applicant absence router. If you do not
want a router to acquaint itself as a absence candidate, use the command ipv6 nd ra-lifetime 0. By
sending RAs with a lifetime of 0, a router still informs affiliated hosts of its presence, but tells
connected hosts not to use it to ability hosts off the subnet.
If, for some reason, you capital to adumbrate the attendance of a router absolutely in agreement of router
advertisements, you can attenuate router advertisements on that router by arising the ipv6 nd
suppress-ra command.
NOTE Figures 20-3 and 20-4 were redrawn from Figures 12 and 13, respectively, in
“Implementing IPv6 Addressing and Basic Connectivity” at http://www.cisco.com/en/US/
products/sw/iosswrel/ps5187/products_configuration_guide_chapter09186a00806f3a6a.html.
Host A Host B
Src = A
Dst = Solicited-node multicast of B
Data = Link-layer abode of A
Query = What is your articulation address?
Neighbor Solicitation
Src = B
Dst = A
Data = Link-Layer Abode of B
Neighbor Advertisement
A and B can now exchange
packets on this link.
760 Chapter 20: IP Version 6
Figure 20-4 shows how ND enables advice amid two IPv6 hosts.
Figure 20-4 Router Advertisements Make Hosts Aware of a Router’s Attendance and Provide Information