Explain Process of IPv6 Stateless Auto-configuration

topology

Configuration Link to heading

hostname R1

ipv6 unicast

int f0/0
    no shut
    ipv6 add autoconfig default

hostname R2

ipv6 unicast

int f0/0
    no shut
    ipv6 add 3F4E:ABCD:1111:1::1/64

Explaination Link to heading

Step 1: R1 builds its link-local address from 48-bit MAC address by 64-bit EUI. Link to heading

Flip the 7th bit of the MAC address:

CA = 1100 1010

Flip: 1100 1000 = C8

Insert FF:FE to the middle of the changed MAC address:

EUI-64 = C803:2DFF:FE64:0023

Insert prefix FE80:: to the begining of the EUI-64 to get the link-local address:

Link-local = FE80::C803:2DFF:FE64:0023

Step 2: R1 checks the unique link-local by sending DAD (Duplicate Address Detection) and NS (Neighbor Solicitation). Link to heading

Step 3: R1 sends RS (Router Solicitation) to find a router which is offering a prefix length. Link to heading

Step 4: R2 responds RA (Router Advertisement) included the prefix length. Link to heading

Prefix length = 3F4E:ABCD:1111:1::/64

Step 5: R1 autoconfigures its IPv6 by combining prefix length and EUI-64. Link to heading

IPv6 = Prefix length + EUI-64

IPv6 = 3F4E:ABCD:1111:1:C803:2DFF:FE64:0023

R1# show int f0/0
FastEthernet0/0 is up, line protocol is up
  Hardware is DEC21140, address is ca03.2d64.0023 (bia ca03.2d64.0023)

R1#debug ipv6 nd
*Jan  7 11:37:27.167: ICMPv6-ND: ND Module startup.
*Jan  7 11:37:27.171: ICMPv6-ND: Initialise OL prefix database
*Jan  7 11:37:27.179: ICMPv6-ND: IPv6 Opr Enabled on Null0
*Jan  7 11:37:27.179: ICMPv6-ND: Allocate ND subblock on Null0 [1]
*Jan  7 11:37:27.191: ICMPv6-ND: L2 came up on Null0
*Jan  7 11:37:27.191: IPv6-Addrmgr-ND: DAD request for FE80::1 on Null0
*Jan  7 11:37:27.195: IPv6-Addrmgr-ND: DAD: FE80::1 is unique.
*Jan  7 11:37:27.195: ICMPv6-ND: L3 came up on Null0
*Jan  7 11:37:27.199: ICMPv6-ND: Linklocal FE80::1 on Null0, Up
*Jan  7 11:37:27.207: ICMPv6-ND: IPv6 Opr Enabled on FastEthernet0/0
*Jan  7 11:37:27.207: ICMPv6-ND: Allocate ND subblock on FastEthernet0/0 [2]
*Jan  7 11:37:27.215: ICMPv6-ND: L2 came up on FastEthernet0/0
*Jan  7 11:37:27.215: IPv6-Addrmgr-ND: DAD request for FE80::C803:2DFF:FE64:23 on FastEthernet0/0
*Jan  7 11:37:27.219: ICMPv6-ND: Sending NS for FE80::C803:2DFF:FE64:23 on FastEthernet0/0
*Jan  7 11:37:27.219: ICMPv6-ND: [default] Select default router
*Jan  7 11:37:27.219: ICMPv6-ND: [default] best rank is 0
*Jan  7 11:37:27.567: ICMPv6-ND: Sending RS on FastEthernet0/0
*Jan  7 11:37:27.603: ICMPv6-ND: Received RA from FE80::C801:13FF:FEB8:0 on FastEthernet0/0
*Jan  7 11:37:27.603: ICMPv6-ND: Created ND Entry Chunk pool
*Jan  7 11:37:27.603: ICMPv6-ND: Glean FE80::C801:13FF:FEB8:0 on FastEthernet0/0
*Jan  7 11:37:27.603: ICMPv6-ND: Neighbour FE80::C801:13FF:FEB8:0 on FastEthernet0/0 : LLA ca01.13b8.0000
*Jan  7 11:37:27.603: ICMPv6-ND: INCMP -> STALE: FE80::C801:13FF:FEB8:0
*Jan  7 11:37:27.603: ICMPv6-ND: [default] inserted router FE80::C801:13FF:FEB8:0/FastEthernet0/0
*Jan  7 11:37:27.603: ICMPv6-ND: [default] Select default router
*Jan  7 11:37:27.603: ICMPv6-ND: [default] best rank is C11
*Jan  7 11:37:27.603: ICMPv6-ND: [default] router FE80::C801:13FF:FEB8:0/FastEthernet0/0 is new best
*Jan  7 11:37:27.603: ICMPv6-ND: [default] Selected new default router
*Jan  7 11:37:27.603: ICMPv6-ND: [default] Install default to FE80::C801:13FF:FEB8:0/FastEthernet0/0
*Jan  7 11:37:27.603: ICMPv6-ND: Prefix : 3F4E:ABCD:1111:1::, Length: 64, Vld Lifetime: 2592000, Prf Lifetime: 604800, PI Flags: C0
*Jan  7 11:37:27.603: ICMPv6-ND: Created OL-prefix root for 0
*Jan  7 11:37:27.603: ICMPv6-ND: New on-link prefix 3FFE:ABCD:1111:1::/64 on FastEthernet0/0/FE80::C801:13FF:FEB8:0, lifetime 2592000
*Jan  7 11:37:27.603: ICMPv6-ND: Autoconfiguring 3FFE:ABCD:1111:1:C803:2DFF:FE64:0 on FastEthernet0/0

R1# show ipv6 int f0/0
FastEthernet0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::C803:2DFF:FE64:0
  No Virtual link-local address(es):
  Stateless address autoconfig enabled
  Global unicast address(es):
    3FFE:ABCD:1111:1:C803:2DFF:FE64:0, subnet is 3FFE:ABCD:1111:1::/64 [EUI/CAL/PRE]
      valid lifetime 2591954 preferred lifetime 604754
  Joined group address(es):
    FF02::1
    FF02::1:FF64:0
  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 30000)
  ND NS retransmit interval is 1000 milliseconds
  Default router is FE80::C801:13FF:FEB8:0 on FastEthernet0/0