WB1 9.5 IPv6 Auto-Configuration

9.5 IPv6 Auto-Configuration

• Use the unique local address FC00:X:0:58::5/64 for R5’s VLAN 58
interface, where X is your rack number in decimal notation.
• Configure an additional IPv6 address of FC00:X:0:85::5/64 on the same
interface of R5.
• Configure R5 to broadcast both prefixes using ICMPv6 ND RAs, but only
allow the hosts to use the second prefix for auto-configuration.
• The valid and preferred lifetime for both prefixes should be set to 4 hours.
• R5 should advertise itself as the default router on the segment every 40
seconds with a lifetime interval of 60 seconds.
• SW2 should learn its IPv6 address on VLAN 58 automatically and use R5
as its default gateway.

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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 suppressra)
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 autoconfiguration,
by using the no-autoconfig keyword.

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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    (我在R5上設定為no ipv6 nd ra suppress)

SW2:
sdm prefer dual-ipv4-and-ipv6 routing
!
interface Vlan 58
ipv6 address autoconfig default   

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Rack1SW2#show ipv6 interface vlan 58
Vlan58 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::20F:34FF:FEFC:6CC6
  No Virtual link-local address(es):
  Stateless address autoconfig enabled
  Global unicast address(es):
    FC00:1:0:85:20F:34FF:FEFC:6CC6, subnet is FC00:1:0:85::/64 [EUI/CAL/PRE]
      valid lifetime 14366 preferred lifetime 14366
  Joined group address(es):
    FF02::1
    FF02::1:FFFC:6CC6
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ICMP unreachables are sent
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds (using 39146)
  Default router is FE80::C004:12FF:FE30:0 on Vlan58
Rack1SW2#

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
PA FC00:1:0:58::/64 [L] Valid lifetime 14400, preferred lifetime 14400
PA FC00:1:0:85::/64 [LA] Valid lifetime 14400, preferred lifetime 14400
Rack1R5#

ICMP Neighbor Discovery events debugging is on
Rack1R5#
Rack1R5#
*Mar  1 11:15:27.205: ICMPv6-ND: REACH -> STALE: FE80::D8B4:129B:CFAB:4619
Rack1R5#
*Mar  1 11:15:43.713: ICMPv6-ND: Request to send RA for FE80::C004:12FF:FE30:0
*Mar  1 11:15:43.717: ICMPv6-ND: Sending RA from FE80::C004:12FF:FE30:0 to FF02::1 on FastEthernet0/0
*Mar  1 11:15:43.721: ICMPv6-ND:     MTU = 1500
*Mar  1 11:15:43.721: ICMPv6-ND:     prefix = FC00:1:0:58::/64 onlink
*Mar  1 11:15:43.721: ICMPv6-ND:             14400/14400 (valid/preferred)
*Mar  1 11:15:43.725: ICMPv6-ND:     prefix = FC00:1:0:85::/64 onlink autoconfig
*Mar  1 11:15:43.729: ICMPv6-ND:             14400/14400 (valid/preferred)
Rack1R5#