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Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
OL-8915-03
Chapter 35 Configuring IPv6 Host Functions
Understanding IPv6
Every interface on IPv6 nodes must have a link-local address that is automatically configured from the
identifier (router MAC address) for an interface and the link-local prefix(FE80::/10). A link-local
address enables a node to communicate with other nodes on the link and can be used to further configure
the node. Nodes can connect to a network and automatically generate global IPv6 addresses without the
need for manual configuration or the help of a server such as a DHCP server.
With IPv6, a router on the link uses router advertisement messages to advertise global prefixes and its
ability to act as a default router for the link. A node on the link can automatically configure global IPv6
addresses by appending its interface identifier (64 bits) to the prefixes (64 bits) included in the router
advertisement messages.
The 128-bit IPv6 addresses configured by a node are then subjected to duplicate-address detection to
ensure their uniqueness on the link. If the advertised prefixes are globally unique, the IPv6 addresses
configured by the node are guaranteed to be globally unique. Router solicitation messages, which have
a value of 133 in the ICMP packet header Type field, are sent by hosts at system startup so that the host
can be immediately autoconfigured without waiting for the next scheduled router advertisement
message.
IPv6 duplicate-address detection is performed on unicast addresses before they are assigned to an
interface. The switch does not support automatically generated site-local IPv6 addresses.
IPv6 Stateless Autoconfiguration
When an IPv6 host (nonrouter) autoconfigures its interfaces, the process includes generating a
link-local, a site-local, and a global address through stateless address autoconfiguration.
IPv6 nodes (routers and hosts) begin the autoconfiguration process by generating a link-local address for
the interface. Link-local address autoconfiguration is started by:
•
Enabling IPv6 on an interface by entering the
ipv6 enable
interface configuration command
•
Manually configuring the IPv6 address
•
Autoconfiguring by entering the
ipv6 address autoconfig
command
A link-local address is formed by appending the interface identifier to the well-known link-local prefix
(FE80::/10). The IPv6 node verifies that the generated tentative address is not used by another node on
the link before the address can be assigned to the interface. To verify this, the IPv6 node sends a neighbor
solicitation with the tentative address as the target address. If another node is detected to be using that
address or is attempting to use that address (duplicate address detection), the node sends a neighbor
solicitation for the target as well. If the tentative link-local address is not available, autoconfiguration
stops and you must manually configure the interface.
IPv6 nodes with a 48-bit MAC address generate an identifier for the autoconfigured address by
inserting 0xFF and 0xFE in the MAC address and reversing the universal/local bit. For example, if an
interface MAC address is 000b.462e.9047, the identifier would be 020b:46ff:fe2e:9047, and the
autogenerated IPv6 ink address would be FE80::20B:46FF:FE2E:9047.
Only IPv6 hosts can autoconfigure stateless addresses of site-local and global addresses that are started
by using
ipv6 address autoconfig
on an interface. An IPv6 host sends router solicitations to the
all-routers multicast group to obtain router advertisements.
IPv6 routers also periodically send router advertisements, but the delay between successive
advertisements is generally a longer duration than for what a host performing autoconfiguration will
wait. Router advertisements contain zero or more prefix information options that contain information
that the stateless address autoconfiguration uses to generate site-local and global addresses.
