IPv6 Auto-Configuration

R5:

ipv6 unicast-routing

!

interface FastEthernet 0/0

ipv6 address fc00:1:0:58::5/64

ipv6 address fc00:1:0:85::5/64

ipv6 nd prefix fc00:1:0:58::/64 14400 14400 no-autoconfig

ipv6 nd prefix fc00:1:0:85::/64 14400 14400

ipv6 nd ra-interval 40

ipv6 nd ra-lifetime 60

no ipv6 nd suppress-ra

SW2:

sdm prefer dual-ipv4-and-ipv6 routing

!

interface Vlan 58

ipv6 address autoconfig default

IPv6 has a special feature called auto-configuration. It replaces many functions served by DHCP in IPv4 networks (yet there is a special DHCPv6 edition of the DHCP protocol). With IPv6 auto-configuration, an IPv6 host may automatically

learn the IPv6 prefixes assigned to the local segment, as well as determine the default routers on that segment. A special type of link-local IPv6 addressing and the ICMPv6 ND (Neighbor Discovery) protocol accomplish this.

Router Advertisements can be sent at a specified interval or the feature can be suppressed completely (“suppress-ra” is enabled by default on Ethernet interfaces. This default behavior can be changed with the no ipv6 nd suppress-ra) depending on how you configure your Cisco router.

 Note:  that you must enable IPv6 unicast routing in order to send router advertisements. The following commands control the IPv6 RA announcements:

ipv6 nd ra-interval                    – specifies the periodic interval to send RAs.

ipv6 nd ra-lifetime                   – specifies the validity interval of the router’s IPv6 address

ipv6 nd prefix                           – manipulates the IPv6 network prefixes included into RA. By default, all prefixes are  included.

You may adjust the interval that the prefix is valid and preferred with every command. Additionally, you may instruct the hosts not to use this prefix for auto-configuration, by using the no-autoconfig keyword.

Rack1SW2#show ipv6 interface vlan 58

Vlan58 is up, line protocol is up

IPv6 is enabled, link-local address is FE80::21B:D4FF:FED4:4D45

Global unicast address(es):

FC00:1:0:85:21B:D4FF:FED4:4D45, subnet is FC00:1:0:85::/64 [PRE]

valid lifetime 14374 preferred lifetime 14374

Joined group address(es):

FF02::1

FF02::1:FFD4:4D45

MTU is 1500 bytes

ICMP error messages limited to one every 100 milliseconds

ICMP redirects are enabled

ND DAD is enabled, number of DAD attempts: 1

ND reachable time is 30000 milliseconds

Default router is FE80::212:FF:FE1C:DAA0 on Vlan58

Rack1R5#debug ipv6 nd

ICMP Neighbor Discovery events debugging is on

Rack1R5#

ICMPv6-ND: Sending RA to FF02::1 on FastEthernet0/0

ICMPv6-ND: MTU = 1500

ICMPv6-ND: prefix = FC00:1:0:58::/64 onlink

ICMPv6-ND: 14400/14400 (valid/preferred)

ICMPv6-ND: prefix = FC00:1:0:85::/64 onlink autoconfig

ICMPv6-ND: 14400/14400 (valid/preferred)

Rack1R5#show ipv6 interface fastEthernet 0/0 prefix

IPv6 Prefix Advertisements FastEthernet0/0

Codes: A - Address, P - Prefix-Advertisement, O - Pool

U - Per-user prefix, D - Default

N - Not advertised, C - Calendar

PD default [LA] Valid lifetime 2592000, preferred lifetime 604800

AP FC00:1:0:58::/64 [L] Valid lifetime 14400, preferred lifetime

14400

AP FC00:1:0:85::/64 [LA] Valid lifetime 14400, preferred lifetime