IPV6 - Addresses

Current configuration of int f0/0 - I manually assigned the mac-address to make it easier to read when the EUI 64 address is assigned.



R1#show run int f0/0
Building configuration...

Current configuration : 139 bytes
!
interface FastEthernet0/0
 mac-address aaaa.aaaa.aaaa
 no ip address
 duplex auto
 speed auto
 ipv6 address 2001::1/64
 ipv6 enable
end

R1#show ipv6 int f0/0
FastEthernet0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::A8AA:AAFF:FEAA:AAAA
  Global unicast address(es):
    2001::1, subnet is 2001::/64
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::1:FF00:1
    FF02::1:FFAA:AAAA
  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
R1#




  
Show ipv6 int f0/0 partially explained:

 FF02::1 -All IPV6 Hosts - In IPV4 this is like 255.255.255.255

 FF02::2 - All IPV6 Multicast Routers

FF02::1:FF00:1  - Solicited-Node multicast address for the global unicast address. This is used by DAD(Duplicate Address Detection) to check if the address is already in use. Everytime you assign an ipv6 address to an interface it will then join the Solicited-Node multicast address for that ipv6 address you assigned.

FF02::1:FFAA:AAAA - Solicited-Node multicast address  for the link-local address 

Enabling Debug for ND(Neighbor Discovery).

R1#debug ipv6 nd
ICMP Neighbor Discovery events debugging is on


R1(config)#int f0/0
R1(config-if)#shut
*Mar  1 00:34:59.247: ICMPv6-ND: Address 2001::1/64 is down on FastEthernet0/0
*Mar  1 00:34:59.247: ICMPv6-ND: Address FE80::A8AA:AAFF:FEAA:AAAA/10 is down on FastEthernet0/0

*Mar  1 00:35:01.243: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administratively down
*Mar  1 00:35:02.243: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to down

R1(config-if)#no shut
*Mar  1 00:35:13.047: ICMPv6-ND: Sending NS for FE80::A8AA:AAFF:FEAA:AAAA on FastEthernet0/0
*Mar  1 00:35:14.035: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
R1(config-if)#
*Mar  1 00:35:14.047: ICMPv6-ND: DAD: FE80::A8AA:AAFF:FEAA:AAAA is unique.
*Mar  1 00:35:14.047: ICMPv6-ND: Sending NA for FE80::A8AA:AAFF:FEAA:AAAA on FastEthernet0/0
*Mar  1 00:35:14.047: ICMPv6-ND: Address FE80::A8AA:AAFF:FEAA:AAAA/10 is up on FastEthernet0/0
*Mar  1 00:35:14.055: ICMPv6-ND: Sending NS for 2001::1 on FastEthernet0/0
*Mar  1 00:35:15.035: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R1(config-if)#
*Mar  1 00:35:15.055: ICMPv6-ND: DAD: 2001::1 is unique.
*Mar  1 00:35:15.055: ICMPv6-ND: Sending NA for 2001::1 on FastEthernet0/0
*Mar  1 00:35:15.055: ICMPv6-ND: Address 2001::1/64 is up on FastEthernet0/0
R1(config-if)#

DAD is run for all ipv6 addresses assigned under f0/0 and keep in mind that even though the link-local address is not assigned manually in this case, DAD is still run for it. This is where the Solicited-Node multicast address comes into play. A NS(Neighbor Solicitation) is sent to that address and if the address is used, you will see an Neighbor Advertisement come back to the device that originated the Neighbor Solicitation). If the address is not in use, you should not see a Neighbor Advertisement from any device. You can see this from the debug output.