7 slaac-rick graziani

7: SLAAC
(Stateless Address Autoconfiguration)
Rick Graziani
Cabrillo College
Rick.Graziani@cabrillo.edu

©
For more information please check out my Cisco Press book and video series:
IPv6 Fundamentals: A Straightforward
Approach to Understanding IPv6
• By Rick Graziani
• ISBN-10: 1-58714-313-5
IPv6 Fundamentals LiveLessons: A
Straightforward Approach to Understanding IPv6
• By Rick Graziani
• ISBN-10: 1-58720-457-6

7.1: Introduction to SLAAC and ICMPv6 ND

©
Dynamic IPv6 Address Allocation
• DHCPv6 and SLAAC with DHCPv6 are discussed in Lesson 8.
Global Unicast
Manual Dynamic
Static
IPv6
unnumbered
Static + EUI 64
SLAAC DHCPv6
SLAAC +
DHCPv6
Similar to IPv4 unnumbered
Stateless Stateful
DHCPv6-PD

©
DHCP Server
Dynamic IPv4 Address Allocation
DHCP Client
I need an IPv4 addressing
information from a DHCP server.
Here is your IPv4
address, subnet mask,
default gateway and
DNS server addresses.

©
ICMPv6
Internet Control Message
Protocol for IPv6
• Described in RFC 4443
• Much more robust than ICMP for IPv4
• Contains new functionality and
improvements.
• More than just “messaging” but “how
IPv6 conducts business”.
• Including ICMPv6 Neighbor Discovery
(RFC 4861) – used in dynamic
address allocation.
• Note: ICMPv6 is discussed in detail in
Lesson 9, ICMPv6 ND in Lesson 10.

©
“Introducing” ICMPv6 Neighbor Discovery
ICMPv6 informational messages used by Neighbor
Discovery (RFC 4861):
• Router Solicitation Message
• Router Advertisement Message
• Used for dynamic address allocation.
• Neighbor Solicitation Message
• Neighbor Advertisement Message
• Used with address resolution (IPv4 ARP)
and with DAD
• Redirect Message (Similar to ICMPv4)
Router-Device
Messaging
Device-Device
Messaging

©
It Begins with the RA Message
• An ICMPv6 Router Advertisement (RA) suggests to all IPv6 devices on the
link how it will receive IPv6 Address Information.
• Sent periodically by an IPv6 router or…
• … when the router receives a Router Solicitation message from a host.
DHCPv6
Server
ICMPv6 Router Advertisement
ICMPv6 Router Solicitation
Multicast: To all
IPv6 routers, I need
IPv6 address
information
Multicast: To all IPv6
devices,
let me suggest to you
how to do this …
I might not even be
needed. 

©
It Begins with the RA Message
Router Advertisement (RA) Message
• Part of ICMPv6 (Internet Control Message Protocol for IPv6)
• RA messages are sent by an “IPv6 router”
• An IPv6 router (ipv6 unicast-routing command):
• Forwards IPv6 Packets
• Enables IPv6 static and dynamic routing
• Sends ICMPv6 Router Advertisements
• Note: Routers can be configured with IPv6 addresses without being an IPv6 router.
DHCPv6
Server
Router(config)# ipv6 unicast-routing

©
Router Advertisement: 3 Options
DHCPv6 Server
RA
Option 1: SLAAC – No DHCPv6 (Default on Cisco routers)
“I’m everything you need (Prefix, Prefix-length, Default Gateway)”
Option 2: SLAAC + Stateless DHCPv6 for DNS address
“Here is my information but you need to get other information such
as DNS addresses from a DHCPv6 server.” (DNS can be in RA)
Option 3: All addressing except default gateway use DHCPv6
“I can’t help you. Ask a DHCPv6 server for all your information.”
DHCPv6
Option 1 and 2: Stateless Address Autoconfiguration
• DHCPv6 Server does not maintain state of addresses
Option 3: Stateful Address Configuration
• Address received from DHCPv6 Server
• Options 2 and 3 are discussed in Lesson 8.

©
RA Message Options
The type of Router Advertisement option depends on two RA flags:
Other Configuration Flag and Managed Configuration Flag
• Default: Both flags are set to 0 (Option 1)
• Use me (RA) for all your addressing information, no additional information available
via DHCPv6.
• Other Configuration Flag when set to “1” (Option 2)
• Use me (RA) for your address but you need to get OTHER information from a
stateless DHCPv6 server.
• Managed Configuration Flag when set to “1” (Option 3)
• The client needs to get ALL of it’s MANAGED information from a stateful DHCPv6
server, except default gateway.
• Note: Two other flags include the autonomous address-configuration flag and on-link flag.
(“A” Flag discussed in lesson 8, “L” Flag beyond the scope of this video.)
DHCPv6
Server
Option 1, 2, or 3

©
RA Message Options
DHCPv6
Server
Option 1, 2, or 3
Option Other Configuration
(“O”) Flag
Managed Configuration
(“M”) Flag
Option 1: SLAAC – No DHCPv6
(Default on Cisco routers)
0 0
Option 2: SLAAC + Stateless
DHCPv6 for DNS address
1 0
Option 3: All addressing except
default gateway use DHCPv6
0 1
• Configuring Flags discussed in Lesson 8.

©
SLAAC: Stateless Address Autoconfiguration
DHCPv6 Server
• Prefix and other information
SLAAC (Stateless Address Autoconfiguration)
• Allows a device to create its own IPv6 global unicast
address without the services of a DHCPv6 server.
• Prefix: From the Router Advertisement (RA).
• Interface ID:
• EUI-64
• Random 64-bit value
2001:DB8:CAFE:1::/64
I know the network prefix
from the RA.
I just need to come up with
my own Interface ID for my
GUA!

©
DHCPv6
DHCPv6 Server
Ignoring the RA Message?
• The ICMPv6 Router Advertisement suggests to the host how to get
its address automatically.
• Can a host ignore an ICMPv6 Router Advertisement?
• Host operating systems can include the option of ignoring the
Router Advertisement from the router and only use the stateful
services of a DHCPv6 server (or what ever it wants to do).
• However, hosts can’t ignore the default gateway (source of RA)
unless manually configured.
ICMPv6 Router
Advertisement
Link-local address

7.2: Creating the Interface ID: EUI-64
or Random Value

©
Obtaining an IPv6 Address Automatically

©
Note: Domain name and DNS server list
may be included if router (and end system)
support RFC 6106 IPv6 RA Options for
DNS Configuration.
SLAAC Option 1 – RA Message
To: FF02::1 (All-IPv6 devices)
From: FE80::1 (Link-local address)
Prefix: 2001:DB8:CAFE:1::
Prefix-length: /64
RA
1
MAC: 00-19-D2-8C-E0-4C
Prefix-length: /64
Default Gateway: FE80::1
Global Unicast Address:
2001:DB8:CAFE:1: + Interface ID
2001:DB8:CAFE:1::/64
EUI-64 Process or
Random 64-bit value
2
DHCPv6 Server
3
SLAAC: Stateless Address Autoconfiguration

©
SLAAC: Interface ID
Global Routing Prefix 64-bit Interface ID
16-bit
Subnet ID
/64/48
EUI-64 Process Randomly Generated Number
(Privacy Extension)
SLAAC
Operating
System
EUI-64 Random
64-bit
Windows XP,
Server 2003 ✔
Windows Vista
and newer ✔
MAC OSX
✔
Linux
✔
DHCPv6 Server
Default OS behavior can be changed.
Known instead of unknown © Copyright DOC RABE Media Man in paper bag on head © Copyright binik

©
Note: Domain name and DNS server list
may be included if router (and end system)
support RFC 6106 IPv6 RA Options for
DNS Configuration.
SLAAC Option 1 – RA Message
To: FF02::1 (All-IPv6 devices)
From: FE80::1 (Link-local address)
Prefix-length: /64
RA
1
MAC: 00-19-D2-8C-E0-4C
Prefix-length: /64
Default Gateway: FE80::1
Global Unicast Address:
2001:DB8:CAFE:1: + Interface ID
2001:DB8:CAFE:1::/64
EUI-64 Process or
Random 64-bit value
2
DHCPv6 Server
3
SLAAC: EUI-64 Option

©
Modified EUI-64 Format (Extended Unique Identifier–64)
00 19 D2 8C E0 4C
OUI (24 bits) Device Identifier (24 bits)
00 19 D2 8C E0 4CFF FE
19 D2 8C E0 4CFF FE0000 000000
U/L bit flipped
0000 0010
02 19 D2 8C E0 4CFF FE
Insert FF-FE

©
PC> ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
IPv6 Address. . . . . . . . : 2001:db8:cafe:1:0219:d2ff:fe8c:e04c
Link-local IPv6 Address . . : fe80::0219:d2ff:fe8c:e04c
Default Gateway . . . . . : fe80::1
Router Advertisement EUI-64
A 64-bit Interface ID and the EUI-64 process accommodates:
• The IEEE specification for a 64-bit MAC address
• 64-bit boundary processing
Verifying SLAAC
on the PC Using
EUI-64
Why. The Dude looking at the red question mark © Copyright jojje11

©
SLAAC: Random 64-bit Interface ID
Global Routing Prefix 64-bit Interface ID
16-bit
Subnet ID
/64/48
EUI-64 Process Randomly Generated Number
(Privacy Extension)
SLAACOperating
System
EUI-64 Random
64-bit
Windows XP,
Server 2003 ✔
Windows Vista
and newer ✔
MAC OSX
✔
Linux
✔
DHCPv6 Server
Known instead of unknown © Copyright DOC RABE Media Man in paper bag on head © Copyright binik

©
PC-Windows7> ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
IPv6 Address. . . . . . . . : 2001:db8:cafe:1:50a5:8a35:a5bb:66e1
Link-local IPv6 Address . . : fe80::50a5:8a35:a5bb:66e1
Default Gateway . . . . . : fe80::1
Router Advertisement EUI-64
Verifying SLAAC
on the PC Using
Privacy Extension
No FF-FE

©
SLAAC: Including the DNS Server in the RA *
DNS Server
• Prefix and other information
G0/1
2001:DB8:CAFE:1::/64
Router(config)# interface gigabitethernet 0/1
Router(config-if)# ipv6 nd ra dns server 2001:db8:cafe:1::99 600
2001:DB8:CAFE:1::99
Configures a DNS server with an IPv6 address of 2001:DB8::CAFE:1::1 to be
advertised in an RA with a lifetime of 600 seconds.

©
Global Unicast - 2001:db8:cafe:1:0219:d2ff:fe8c:e04c
Link-local - fe80::50a5:8a35:a5bb:66e1
Neighbor Advertisement?
Neighbor Solicitation
Ensuring Unique Unicast Addresses
Not received = unique address
Received = duplicate address
• SLAAC is stateless, no entity (DHCPv6 server) maintaining a state address-
to-device mappings.
• How can we guarantee the address is unique?
• Duplicate Address Detection (DAD)
• Once required for all unicast addresses (static or dynamic), RFC was
updated that DAD is only recommended.
• /64 Interface IDs!

7.3: Configuring a Router as a
SLAAC Client

©
Routers versus IPv6 Routers
• A router (not enabled as an IPv6 router):
• Configure IPv6 addresses
• Member of All-IPv6 devices multicast group
• An IPv6 router:
• Same as a non-IPv6 router
• Member of All-IPv6 routers multicast group
• Sends ICMPv6 Router Advertisement messages
• Can enable IPv6 routing protocols
• Forward IPv6 packets (transiting the router)
Router IPv6 Router
2001:DB8:CAFE:1::1/64
FE80::1
2001:DB8:CAFE:1::1/64
FE80::1
FF02::1 (All-IPv6 devices) FF02::1 (All-IPv6 devices)
FF02::2 (All-IPv6 routers)
ICMPv6 Router
Advertisement
Forward IPv6 Packets
RIPng OSPFv3
EIGRP for IPv6

©
R1 Client
Client(config)# interface gig 0/1
Client(config-if)# ipv6 enable ! Not needed
Client(config-if)# ipv6 address autoconfig default
Client(config-if)# no shutdown
Gig 0/1Gig 0/1
R1(config)# interface gig 0/1
R1(config-if)# ipv6 address 2001:db8:cafe:1::1/64
R1(config-if)# ipv6 address fe80::1 link-local
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# ipv6 unicast-routing
Configuring the Router as a Client
2001:DB8:CAFE:1::/64
“IPv6 Router” Link-local address
created
Now I can accept
RA messages and
get a GUA
automatically!

©
R1 ClientGig 0/1Gig 0/1
::1
R1# show ipv6 interface gigabitethernet 0/1
GigabitEthernet0/1 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::1
Global unicast address(es):
2001:DB8:CAFE:1::1, subnet is 2001:DB8:CAFE:1::/64
Joined group address(es):
FF02::1
FF02::2
FF02::FB
FF02::1:FF00:1
ND router advertisements are sent every 200 seconds
Hosts use stateless autoconfig for addresses.
Verifying the RA Message
2001:DB8:CAFE:1::/64
Partial output
FE80::1

©
::1
Client# show ipv6 interface brief
GigabitEthernet0/1 [up/up]
FE80::8A5A:92FF:FE3B:29E1
2001:DB8:CAFE:1:8A5A:92FF:FE3B:29E1
<Rest of output omitted>
Client# show interface gigabitethernet 0/1
GigabitEthernet0/1 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is 885a.923b.29e1 (bia
885a.923b.29e1)
Verifying the Client (Router) Is Using SLAAC/EUI-64
2001:DB8:CAFE:1::/64
FE80::1
EUI-64

©
::1
Client# show ipv6 route
IPv6 Routing Table - default - 4 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external
ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ND ::/0 [2/0]
via FE80::1, GigabitEthernet0/1
NDp 2001:DB8:CAFE:1::/64 [2/0]
via GigabitEthernet0/1, directly connected
Router versus “IPv6 Router”
2001:DB8:CAFE:1::/64
Partial output
FE80::1
Default route learned via Neighbor
Discovery (SLAAC)
Prefix learned via Neighbor
Discovery (SLAAC)

7.4: IPv6 Enabled Clients and
Your Network

©
You Are Probably Already Running IPv6
• Windows Vista or later, Mac OSX, Linux already running IPv6
• Potential DoS or MITM attack, even if the router is not IPv6 enabled.
• Even if the router is not IPv6 enabled, your clients are mostly like are!
• I can still do a DoS attack on clients or perhaps even still to a MITM
attack.
• There are mitigation techniques such as RA Guard.
R1
Rogue
RA
RS
IPv4
IPv6IPv4
IPv6
IPv4
IPv6
I need an
IPv6 prefix
Here is an
IPv6 prefix
and
gateway
People Icon: Occupations set 5 © Copyright Fredy Sujono

©
SLAAC with DHCPv6
Global Unicast
Manual
Static
IPv6
unnumbered
Static + EUI 64
SLAAC DHCPv6
SLAAC +
DHCPv6
Similar to IPv4 unnumbered
Stateless Stateful
DHCPv6-PD
Dynamic
Stateful
Lesson 8

7 slaac-rick graziani

More Related Content

What's hot (20)

Viewers also liked (8)

Similar to 7 slaac-rick graziani (20)

Recently uploaded (20)

7 slaac-rick graziani

Editor's Notes