10: ICMPv6 Neighbor Discovery
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
©
10.1: Introducing ICMPv6
Neighbor Discovery
ICMPv6 Neighbor Discover Protocol
ICMPv6 Neighbor Discovery defines 5 different packet types:
• Router Solicitation Message
• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message
• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message
Similar to ICMPv4 redirect message
Router-to-Device messaging
Router-Device
Messaging
Device-Device
Messaging
See these processes with:
R1# debug ipv6 nd
©
ICMPv6 Redirect
Network X
R1
R2
Destination:
Network
PCB
X Host
IPv6
Network A PCA
•
•
•
PCB
IPv6
Network B
Similar functionality as ICMPv4.
Like IPv4, a router informs an originating host of the IP address of a router that
is on the local link and is closer to the destination.
Unlike IPv4, a router informs an originating host that the destination host (on a
different prefix/network) is on the same link as itself.
©
10.2: Router Solicitation and
Router Advertisement Messages
Dynamic Address Allocation in IPv4
DHCPv4 Server
1
2
I need IPv4
addressing
information.
Here is everything
you need.
©
Dynamic Address Allocation in IPv6
Router(config)# ipv6 unicast-routing
To all IPv6 routers:
I need IPv6 address
information.
I might not be
needed.
ICMPv6 Router Solicitation
DHCPv6 Server
To all IPv6 devices:
Let me tell you how
to do this …
ICMPv6 Router Advertisement
1. SLAAC
2. SLAAC with
Stateless DHCPv6
SLAAC
(Stateless Address Autoconfiguration)
3. Stateful DHCPv6
©
RA Message Options
ICMPv6 Router Advertisement
Option 1, 2, or 3
Option
Other Configuration
(“O”) Flag
DHCPv6
Server
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.
©
Option 3 and the “A” Flag
G 0/1
As a Windows host I will still
use the RA prefix to create
temporary (SLAAC) addresses)
ICMPv6 RA
M Flag = 1
A Flag = 10
DHCPv6
DHCPv6 Server
Option
Managed
Configuration
(“M”) Flag
Option 3: All addressing
The autonomous
except
default gateway address
use
DHCPv6
they
can create an address
Address
Autoconfiguration
(“A”) Flag
Prefix in RA can
be used for
SLAAC
1
1 (default)
Yes
configuration (A) flag tells hosts that
for themselves by combining the prefix
Option
All addressing
in the3:RA
with an interface identifier.
1
0
No
except default gateway
use DHCPv6
Configuring Flags discussed in Lesson 8.
©
Router Solicitation / Router Advertisement
2001:DB8:CAFE:1::/64
R1
Link-local: FE80::1
MAC: 00-03-6b-e9-d4-80
Router Solicitation
• Sent when device needs IPv6
addressing information.
Router Advertisement
• Sent every 200 seconds or in
response to RS
To:
Link-local: FE80::50A5:8A35:A5BB:66E1
MAC: 00-21-9b-d9-c6-44
PC1
1
To:
FF02::2 (All-IPv6 Routers)
RS From: FE80::50A5:8A35:A5BB:66E1
ICMPv6 Router Solicitation
2
FF02::1 (All-IPv6 devices)
From: FE80::1 (Link-local address)
RA
ICMPv6 Router Advertisement
©
Analyzing the Router Solicitation Message
©
Ethernet II, Src: 00:21:9b:d9:c6:44, Dst: 33:33:00:00:00:02
Ethernet multicast MAC address – Maps to “all IPv6 routers”
Internet Protocol Version 6
0110 .... = Version: 6 [Traffic class
Payload length: 16
Next header: ICMPv6 (0x3a)
Hop limit: 255
Source: fe80::50a5:8a35:a5bb:66e1
Destination: ff02::2
and Flowlabel not shown]
Next header is an ICMPv6 header
Link-local address of PC1
All-IPv6-routers multicast address
Internet Control Message Protocol v6
Type: 133 (Router solicitation)
Router Solicitation message
Code: 0
Checksum: 0x3277 [correct]
ICMPv6 Option (Source link-layer address)
Type: Source link-layer address (1)
Length: 8
MAC address of PC1 but RA
Link-layer address: 00:21:9b:d9:c6:44
is sent as all-IPv6-host multicast
Router Solicitation Message
©
Analyzing the Router Advertisement Message
©
R1(config)# ipv6 unicast-routing
An IPv6 Router
R1# show ipv6 interface gigabitethernet 0/0
GigabitEthernet0/0 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
All-routers multicast group
FF02::1:FF00:1
MTU is 1500 bytes
<output omitted for brevity>
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
M & O flags = 0
©
Analyzing the Router
Advertisement Message
Ethernet II, Src: 00:03:6b:e9:d4:80, Dst: 33:33:00:00:00:01
Ethernet multicast MAC address – Maps to “All-IPv6 devices”
Internet Protocol Version 6
0110 .... = Version: 6
.... 1110 0000 .... .... .... .... .... = Traffic class: 0x000000e0
.... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
Payload length: 64
Next header: ICMPv6 (0x3a)
Next Header is an ICMPv6 header
Hop limit: 255
Link-local address of R1. Added to hosts’ Default Router List
Source: fe80::1
and is the address they will use as their default gateway.
Destination: ff02::1
All-IPv6 devices multicast
Continued next slide
©
Internet Control Message Protocol v6
Type: 134 (Router advertisement)
Router Advertisement
Code: 0
Cur hop limit: 64
Recommended Hop Limit value for hosts
Flags: 0x00
M and O flags indicate that no information is available via DHCPv6
ICMPv6 Option (Source link-layer address)
Type: Source link-layer address (1)
Length: 8
Link-layer address: 00:03:6b:e9:d4:80
Router R1’s MAC address
ICMPv6 Option (MTU)
Type: MTU (5)
Length: 8
MTU: 1500
MTU of the link.
ICMPv6 Option (Prefix information)
Type: Prefix information (3)
Length: 32
Prefix-length (/64) to be used for autoconfiguration.
Prefix Length: 64
Prefix of this network to be used for
Prefix: 2001:db8:cafe:1::
autoconfiguration
Router Advertisement Message
©
10.3: Neighbor Solicitation and
Neighbor Advertisement Messages
Address Resolution: IPv4 and IPv6
ARP Request: Broadcast
IPv4: ARP over Ethernet
Ethernet
ARP Request/Reply
ARP
Cache
My IPv4!
Here is the
MAC?
PC2
2
1
ARP Reply
ARP Request
1
2
My IPv6!
Here is the
MAC?
PC1
Neighbor
Solicitation
Neighbor
Advertisement
Neighbor
Cache
Know
IPv4, what
is the
MAC?
Know
IPv6, what
is the
MAC?
IPv6: ICMPv6 over IPv6 over Ethernet
NS: Multicast NS: Solicited Node Multicast
Ethernet
IPv6 Header
ICMPv6: Neighbor Solicitation/Advertisement
©
Neighbor Solicitation and Neighbor Advertisement
2001:DB8:CAFE:1::100/64
2001:DB8:CAFE:1::200/64
FF02::1:FF00:200 (Solicited Node Multicast)
PC2
MAC Address
00-1B-24-04-A2-1E
MAC Address
00-21-9B-D9-C6-44
PC1
1
PC1> ping 2001:DB8:CAFE:1::200
4
3
Neighbor
Solicitation
Neighbor
Advertisement
2
Neighbor Cache
<empty until step 5>
NS: Multicast NS: Solicited Node Multicast
Ethernet
NA: Unicast
IPv6 Header
ICMPv6: Neighbor Solicitation/Advertisement
NA: Unicast
©
5
Neighbor Solicitation
2001:DB8:CAFE:1::200/64
FF02::1:FF00:200 (Solicited Node Multicast)
PC2
MAC Address
00-1B-24-04-A2-1E
2001:DB8:CAFE:1::100/64
MAC Address
00-21-9B-D9-C6-44
Neighbor
Solicitation
PC1
Neighbor
Cache
I know the
IPv6, but
what is the
MAC?
©
PC1
NS
Ethernet II, Src: 00:21:9b:d9:c6:44, Dst: 33:33:ff:00:02:00
Internet Protocol Version 6
Mapped multicast address for PC2
0110 .... = Version: 6
.... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000
.... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
Payload length: 32
Next header is an ICMPv6 header
Next header: ICMPv6 (0x3a)
Hop limit: 255
Source: 2001:db8:cafe:1::100
Global unicast address of PC1
Destination: ff02::1:ff00:200
Solicited-node multicast address of PC2
Internet Control Message Protocol v6
Neighbor Solicitation message
Type: 135 (Neighbor solicitation)
Code: 0
Checksum: 0xbbab [correct]
Target IPv6 address, needing
Reserved: 0 (Should always be zero)
MAC address (if two devices
Target: 2001:db8:cafe:1::200
have the same solicited node
ICMPv6 Option (Source link-layer address)
address, this resolves the issue)
Type: Source link-layer address (1)
Length: 8
MAC address of the sender, PC1
Link-layer address: 00:21:9b:d9:c6:44
©
Neighbor Advertisement
2001:DB8:CAFE:1::200/64
FF02::1:FF00:200 (Solicited Node Multicast)
PC2
MAC Address
00-1B-24-04-A2-1E
2001:DB8:CAFE:1::100/64
MAC Address
00-21-9B-D9-C6-44
PC1
Neighbor Cache
It’s my IPv6
and here is
my MAC?
Neighbor
Advertisement
©
PC2
NA
Ethernet II, Src: 00:1b:24:04:a2:1e, Dst: 00:21:9b:d9:c6:44
Internet Protocol Version 6
Unicast MAC address of PC1
0110 .... = Version: 6
.... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000
.... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
Payload length: 32
Next header: ICMPv6 (0x3a)
Next header is an ICMPv6 header
Hop limit: 255
Global unicast address of PC2
Source: 2001:db8:cafe:1::200
Destination: 2001:db8:cafe:1::100
Global unicast address of PC1
Internet Control Message Protocol v6
Neighbor Advertisement message
Type: 136 (Neighbor advertisement)
Code: 0
Checksum: 0x1b4d [correct]
Flags: 0x60000000
Target: 2001:db8:cafe:1::200
IPv6 address of the sender, PC2
ICMPv6 Option (Target link-layer address)
Type: Target link-layer address (2)
Length: 8
MAC address of the sender, PC2
Link-layer address: 00:1b:24:04:a2:1e
©
ICMPv6 Duplicate Address Detection (DAD)
PC2
Global Unicast - 2001:DB8:CAFE:1::200
Link-local
- FE80::1111:2222:3333:4444
Neighbor Solicitation
See the process with:
R1# debug ipv6 nd
Hopefully no
Neighbor Advertisement
• Duplicate Address Detection (DAD) is used to guarantee that an IPv6 unicast
address is unique on the link.
• A device will send a Neighbor Solicitation for its own unicast address (static or
dynamic).
• After a period of time, if a NA is not received, then the address is deemed
unique.
• Once required, RFC was updated to where it is only recommended - /64
Interface ID makes duplicates unlikely!
©
10.4: Neighbor Cache
Neighbor Cache
Neighbor Solicitation
Neighbor Cache
IPv6 Address
MAC Address
2001:DB8:ACAD:1::10
0021.9bd9.c644
?
•
•
Neighbor Advertisement
PC1
IPv6 - 2001:DB8:ACAD:1::10
MAC - 0021.9bd9.c644
Neighbor Cache – Maps IPv6 addresses with Ethernet MAC addresses
• Similar to ARP Cache for IPv4
5 States (2 noticeable and 3 transitory):
• Reachable: Packets have recently been received providing confirmation that
this device is reachable.
• Stale: A certain time period has elapsed since a packet has been received from
this address.
• Transitory States: INCOMPLETE, DELAY, PROBE
©
Neighbor Cache
R1# show ipv6 neighbors
IPv6 Address
FE80::50A5:8A35:A5BB:66E1
2001:DB8:AAAA:1::100
Age Link-layer Addr State Interface
16 0021.9bd9.c644 STALE Fa0/0
16 0021.9bd9.c644 STALE Fa0/0
R1# ping 2001:db8:aaaa:1::100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:AAAA:1::100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
R1# show ipv6 neighbors
IPv6 Address
Age Link-layer Addr State Interface
FE80::50A5:8A35:A5BB:66E1
16 0021.9bd9.c644 STALE Fa0/0
2001:DB8:AAAA:1::100
0 0021.9bd9.c644 REACH Fa0/0
R1#
©
Neighbor Cache FSM
Neighbor Cache (“ARP Cache”)
See the process with:
R1# debug ipv6 nd
No Entry Exists
Neighbor Solicitation (NS) sent
Incomplete
3 NS sent with no NA returned
Reachable Time exceeded (default 30 sec)
Reachable
Or
Unsolicited NA received
Packet returned (TCP increasing ACK)
NA received
NS sent and
NA received
5 sec Probe
Stale – no action required Packet sent Delay
(Resolution pending)
(Reresolution in progress)
(Requires resolution again)
3 NS sent with no NA returned
©
Neighbor Cache
R1# debug ipv6 nd
ICMP Neighbor Discovery events debugging is on
R1# ping 2001:db8:aaaa:1::100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:AAAA:1::100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
*Oct 16 01:41:51.575: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) Resolution request
*Oct 16 01:41:51.575: ICMPv6-ND: Created ND Entry Chunk pool
*Oct 16 01:41:51.575: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) DELETE -> INCMP
*Oct 16 01:41:51.575: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) Sending NS
*Oct 16 01:41:51.575: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) Queued data for
resolution
*Oct 16 01:41:51.579: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) Received NA from
2001:DB8:AAAA:1::100
*Oct 16 01:41:51.579: ICMPv6-ND: Validating ND packet options: valid
*Oct 16 01:41:51.579: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) LLA c471.fe7d.9c29
*Oct 16 01:41:51.579: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) INCMP -> REACH
*Oct 16 01:42:21.639: ICMPv6-ND: (GigabitEthernet0/1,2001:DB8:AAAA:1::100) REACH -> STALE
R1#
©
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
©
10: ICMPv6 Neighbor Discovery
Rick Graziani
Cabrillo College
Rick.Graziani@cabrillo.edu