Information Technology Reference
In-Depth Information
The IPv6 ND protocol performs the following functions:
Stateless address autoconfiguration:
The host can determine its full IPv6 address
without the use of DHCP.
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Duplicate address detection:
The host can determine whether the address it will
use is already in use on the network.
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Prefix discovery:
The host finds out the link's IPv6 prefix.
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Parameter discovery:
The host finds out the link's MTU and hop count.
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Address resolution:
The host can determine the MAC address of other nodes with-
out the use of ARP.
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Router discovery:
The host finds local routers without the use of DHCP.
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Next-hop determination:
The host can determine a destination's next hop.
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Neighbor unreachability detection:
The host can determine whether a neighbor is
no longer reachable.
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Redirect:
The host can tell another host if a preferred next hop exists to reach a par-
ticular destination.
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IPv6 ND uses ICMPv6 to implement some of its functions. These ICMPv6 messages are
Router Advertisement (RA):
Sent by routers to advertise their presence and link-
specific parameters
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Router Solicitation (RS):
Sent by hosts to request RA from local routers
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Neighbor Solicitation (NS):
Sent by hosts to request link layer addresses of other
hosts (also used for duplicate address detection)
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Neighbor Advertisement (NA):
Sent by hosts in response to an NS
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Redirect:
Sent to a host to notify it of a better next hop to a destination
The link address resolution process uses NS messages to obtain a neighbor's link layer ad-
dress. Nodes respond with a NA message that contains the link layer address.
IPv6 Name Resolution
Name resolution for IPv6 addresses can be static or dynamic. Just as with IPv4, static
names to IPv6 addresses can be manually configured in the host configuration file. Dy-
namic name resolution relies on the Domain Name System (DNS).
IPv4 uses A records to provide FQDN name-to-IPv4 address resolution. DNS adds a re-
source record (RR) to support name-to-IPv6-address resolution. RFC 3596 describes the
addition of a new DNS resource record type to support transition to IPv6 name resolu-
tion. The new record type is AAAA, commonly known as “quad-A.” Given a domain
name, the AAAA record returns an IPv6 address to the requesting host.
RFC 2874 specifies another DNS record for IPv6; it defines the A6 resource record. The
RR. But RFC 3363 has changed the status of the A6 RR to deprecated.
