ICMPv6 & Neighbor Discovery Protocol: Learn It Rick Graziani CS/CIS Instructor Cabrillo College

1© 2012 Cisco Systems, Inc. All rights reserved. Cisco confidential.Cisco Networking Academy, US/Canada

ICMPv6 & Neighbor Discovery Protocol: Learn ItRick GrazianiCS/CIS InstructorCabrillo College

Topics In this Presentation andAn Introduction to ICMPv6


Internet Control Message Protocol (ICMPv6) • 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”.

• General message similar to ICMP for IPv4

• Also uses Type and Code fields like in ICMPv4.

• Two types of ICMPv6 messages• Error messages • Informational messages


ICMPv6 Messages• The ICMPv6 error messages are:

• Destination Unreachable• Packet Too Big• Time Exceeded• Parameter Problem

• ICMPv6 informational messages used by the ping command:• Echo Request• Echo Reply

Similar to ICMP for IPv4.Quick look at these first.

We will familiarize ourselves with the IPv6 version of these.


ICMPv6 Messages• ICMPv6 informational messages used for Multicast Listener Discovery

(RFC 2710 ):• Multicast Listener Query• Multicast Listener Report• Multicast Listener Done

• ICMPv6 informational messages used by Neighbor Discovery (RFC 4861):• Router Solicitation Message• Router Advertisement Message• Neighbor Solicitation Message• Neighbor Advertisement Message• Redirect Message

Similar to IGMP (Internet Group Message Protocol) for IPv4.We won’t be covering these.

Most of our time will be spent on the first four of these.Redirect Message is similar to Redirect Messages for IPv4.


ipv6 unicast-routing

PC1R12001:0DB8:AAAA:0001::/64

MAC Address00-21-9B-D9-C6-44

2Neighbor Solicitation MessageFrom: :: (Unspecified source address)To: FF02::1:FFBB:66E1 (Solicited Node Multicast)Target IPv6 Address: FE80::50A5:8A35:A5BB:66E1

Link-local address (Tentative)

NDP Router Advertisement From: FE80::1 To: FF02::1 (All-nodes multicast)

NDP Router Solicitation From: FE80::50A5:8A35:A5BB:66E1 To: FF02::2 (All-routers multicast)

3

4

6 Neighbor Solicitation MessageFrom: :: (Unspecified source address)To: Solicited Node MulticastTarget IPv6 Address:

Addressing Information Added5

1Link-local address automatically created

DAD performed onLink-local address

Global unicast address created using SLAAC

DAD performed on global unicast address

Stateless Address Autconfiguration



3

4

2001:DB8:AAAA:1::100/64

PC1

R1

Neighbor Solicitation MessageFrom Ethernet MAC address: 00-21-9B-D9-C6-44To Ethernet MAC address: 33-33-FF-00-02-00 (IPv6 Mapped Multicast)

From: 2001:DB8:AAAA:1::100To: FF02::1:FF00:200 (Solicited Node Multicast)

Target IPv6 Address: 2001:DB8:AAAA:1::200Link-layer address: 00:21:9B:D9:C6:44

PC2

2001:0DB8:AAAA:0001::/64

2001:DB8:AAAA:1::200/64FF02::1:FF00:200 (Solicited Node Multicast)

Neighbor Advertisement MessageFrom Ethernet MAC address: 00-1B-24-04-A2-1ETo Ethernet MAC address: 00-21-9B-D9-C6-44

From: 2001:DB8:AAAA:1::200To: 2001:DB8:AAAA:1::100

Target IPv6 Address: 2001:DB8:AAAA:1::200Link-layer address: 00:1B:24:04:A2:1E


MAC Address00-1B-24-04-A2-1E

PC1> ping 2001:DB8:AAAA:1::200 1Neighbor Cache<empty until step 5>

2 5

Address Resolution (ARP in IPv4)


No Entry Exists Incomplete

Reachable

Stale – no action required(Requires reresolution)

Delay(Resolution pending)

Probe(Reresolution in progress)

Neighbor Solicitation (NS) sent

Neighbor Advertisement (NA) received

Reachable Time exceeded (timeout)OrUnsolicited NA received

Packet sentPacket returned

5 sec

NS sent andNa received

3 NS sent with no NA

• Neighbor Solicitation (NS) = ARP Request

• Neighbor Advertisement (NA) = ARP Reply

3 NS sent with no NA

Neighbor Cache (“ARP Cache”)Neighbor Cache FSM

General Message Format

ICMPv6 Error Messages


IPv6 Next Header Value: 58 decimal or 3A hexadecimal

IPv6 Header

Next Header58

ICMPv6 Header

ICMPv6 Message Body

IPv6 Data

ICMPv6 General Message Format (similar to ICMP for IPv4)

Type Code Checksum

8 16 3224

Message Body

Next Header and General Message Format


The first messages we will examine…• The ICMPv6 error messages are:




We will familiarize ourselves with the IPv6 version of these.


Destination Unreachable Message

• Sent when a packet cannot be delivered to its destination for reasons other than congestion.

• A router (or a firewall) usually generates these messages.

• Various code values give more detail, such as (4) port unreachable.


Packet Too Big Message

• Important difference with IPv6…

• IPv4 routers fragment a packet when the MTU (Maximum Transmission Unit) of the outgoing link is smaller than the size of the packet. • The destination device is responsible for reassembling the fragmented

packets.

• IPv6 routers do not fragment packets (unless it is the source of the packet).


Source DestinationMTU = 1500 MTU = 1500 MTU = 1350 MTU = 1500

IPv6 Packet with MTU = 1,500 bytes

ICMPv6 Packet Too Big message, use MTU 1,350

IPv6 Packet with MTU = 1,350 bytes

1

2

3

Packet Received4

R1 R2 R3

PC-APC-B

Path MTU DiscoveryMTU of outgoing link smaller than

packet size – drop packet


Time Exceeded Message

• Before a router forwards an IPv6 packet it decrements the Hop Limit field by one.

• If the Hop Limit (same as TTL in IPv4) results in a zero

• Packet is dropped and a Time Exceeded message is sent to the source.


Parameter Problem Message

• Generated when a receiving device finds a problem with a field in the main IPv6 header such as the Next Header field.

• Means the device didn’t understand the information in the IPv6 header and had to discard it.

ICMPv6 Informational Messages:Echo Request and Echo Reply


Type = 128 or 129 Code = 0 Checksum

8 16 3224

Data

Identifier Sequence Number

Echo Reply: Type = 128Echo Request: Type = 129

• Like for IPv4, ICMPv6 Echo Request and Echo Reply are two ICMP messages used by ping.

ICMPv6 Echo Request and Echo Reply Messages


IPv6 Topology

2001:0DB8:AAAA:1::100FE80::50A5:8A35:A5bb:66E1

2001:0DB8:AAAA:1::200

2001:0DB8:AAAA:2::/64

2001:0DB8:AAAA:1::/64

Fa0/0 .1Fa0/1 .1 Fa0/0 .2

R1 R2

2001:0DB8:AAAA::/48

FE80::1/64FE80::1/64 FE80::2/64

PC1 PC2


Ping global unicast address from PC1 to R1

PC1> ping 2001:db8:aaaa:1::1

Pinging 2001:db8:aaaa:1::1 from 2001:db8:aaaa:1::100 with 32 bytes of data:

Reply from 2001:db8:aaaa:1::1: time=1msReply from 2001:db8:aaaa:1::1: time=1msReply from 2001:db8:aaaa:1::1: time=1msReply from 2001:db8:aaaa:1::1: time=1ms

Ping statistics for 2001:db8:aaaa:1::1: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),Approximate round trip times in milli-seconds: Minimum = 1ms, Maximum = 1ms, Average = 1ms

PC1>


Echo Request from PC1 to R1Internet Protocol Version 6 0110 .... = Version: 6 .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000 .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000 Payload length: 40 Next header: ICMPv6 (0x3a) Hop limit: 128 Source: 2001:db8:aaaa:1::100 Destination: 2001:db8:aaaa:1::1

Internet Control Message Protocol v6 Type: 128 (Echo (ping) request) Code: 0 (Should always be zero) Checksum: 0x8f38 [correct] ID: 0x0001 Sequence: 0 Data (32 bytes)


Internet Protocol Version 6 0110 .... = Version: 6 .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000 .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000 Payload length: 40 Next header: ICMPv6 (0x3a) Hop limit: 64 Source: 2001:db8:aaaa:1::1 Destination: 2001:db8:aaaa:1::100

Internet Control Message Protocol v6 Type: 129 (Echo (ping) reply) Code: 0 (Should always be zero) Checksum: 0x8e38 [correct] ID: 0x0001 Sequence: 0 Data (32 bytes)

Echo Reply from R1 to PC1


R1# ping fe80::50a5:8a35:a5bb:66e1Output Interface: fastethernet 0/0% Invalid interface. Use full interface name without spaces (e.g. Serial0/1)Output Interface: fastethernet0/0Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to FE80::50A5:8A35:A5BB:66E1, timeout is

2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 msR1#

Ping link-local address from R1 to PC1


Echo Request: Link-local address from R1 to PC1Internet Protocol Version 6 0110 .... = Version: 6 .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000 .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000 Payload length: 60 Next header: ICMPv6 (0x3a) Hop limit: 64 Source: fe80::1 Destination: fe80::50a5:8a35:a5bb:66e1

Internet Control Message Protocol v6 Type: 128 (Echo (ping) request) Code: 0 (Should always be zero) Checksum: 0x0444 [correct] ID: 0x0a24 Sequence: 0 Data (52 bytes)


Internet Protocol Version 6 0110 .... = Version: 6 .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000 .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000 Payload length: 60 Next header: ICMPv6 (0x3a) Hop limit: 64 Source: fe80::50a5:8a35:a5bb:66e1 Destination: fe80::1

Internet Control Message Protocol v6 Type: 129 (Echo (ping) reply) Code: 0 (Should always be zero) Checksum: 0x0344 [correct] ID: 0x0a24 Sequence: 0 Data (52 bytes)

Echo Reply: Link-local address from PC1 to R1

ICMPv6 Informational MessagesUsed by Neighbor Discovery

Router Solicitation MessageRouter Advertisement MessageNeighbor Solicitation MessageNeighbor Advertisement MessageRedirect Message

Router Solicitation & Router Advertisement Messages

andSLAAC (Stateless Address

Autoconfiguration)


Hosts and Addressing• Static configuration

• Stateless Address Autoconfiguration (SLAAC)• SLAAC only

• SLAAC with DHCPv6

• Note: Host OS determines if it will use EUI-64 or random value for Interface ID

• Stateful Autoconfiguration• DHCPv6 only


Stateless Address Autoconfiguration (SLAAC)

• Stateless Address Autoconfiguration (SLAAC) is an automatic method for assigning global unicast addresses to interfaces. • Defined in RFC 4862, IPv6 Stateless Address Autoconfiguration

• Uses:• Prefix and other information from -> ND Router Advertisement• Interface ID from -> IEEE modified EUI-64 format or random value

• No need for DHCPv6 server (unless need DNS)

NDP Router Solicitation


1

2

MAC: 00-19-D2-8C-E0-4C

RouterA

EUI-64NDP Router Advertisement


ipv6 unicast-routingR1

DHCPv6 Server

R1(config)# ipv6 unicast-routing

• Router Solicitation and Router Advertisement messages are about communications between a host and a router.

• Router Advertisement includes:• Prefix, prefix-length, default-gateway, MTU, Hop limit and more.

NDP Router AdvertisementNDP Router Solicitation “Need information from the router”

Time for me to send out a Router

AdvertisementI just booted up, send

me a Router Advertisement



2

R1

DHCPv6 Server

NDP Router Solicitation “Need information from the router”

1

• The router’s Router Advertisement can determine how the host gets its dynamic address configuration.

• ipv6 unicast-routing command enables router to send Router Advertisements.

NDP Router Advertisement “I’m everything you need (Prefix, Prefix-length, Default Gateway)” Or“Here is my information but you need to get other information such as DNS addresses from a DHCPv6 server.”Or“I can’t help you. Ask a DHCPv6 server for all your information.”


NDP Router Advertisement Prefix: 2001:DB8:AAAA:1:: Prefix-length: /64To: FF02::1 (All-hosts multicast)From: FE80::1 (Link-local address)



12

3

MAC: 00-19-D2-8C-E0-4C

Prefix: 2001:DB8:AAAA:1:: Prefix-length: /64EUI-64 Interface ID: 02-19-D2-FF-FE-8C-E0-4CGlobal Unicast Address: 2001:DB8:AAAA:1:0219:D2FF:FE8C:E04CDefault Gateway: FE80::1 (Default Router List)

PC1> ipconfig IPv6 Address. . . . . . : 2001:DB8:AAAA:1:0219:D2FF:FE8C:E04C Default Gateway . . . . : fe80::1

R1

EUI-64

Duplicate Address Detection (DAD)4


NDP Router Advertisement “Here is my information but you need to get other information such as DNS addresses from a DHCPv6 server.”Or“I can’t help you. Ask a DHCPv6 server for all your information.”



1

2 3

R1

4 DHCPv6 Advertise Message“I’m a DHCPv6 Server.”

DHCPv6 Solicit Message“I need a DHCPv6 Server.”

DHCPv6 Server

5 DHCPv6 Request Message“I need addressing information.

6 DHCPv6 Reply Message“Here is your address and other information.”

Stateless AddressingDHCPv6 Addressing

Duplicate Address Detection (DAD)7


ICMPv6 Router Solicitation Message

Type = 133 Code = 0 Checksum

8 16 3224

Valid Options:Source link-layer address

Reserved

ICMPv6 Router Advertisement Message

Type = 134 Code = 0 Checksum8 16 3224

Possible Options: Source link-layer address MTU Prefix Information

Reachable Time

Retrans Time

Cur Hop Limit Reserved Router LifetimeM O

A closer look at the protocol


NDP Router Advertisement From: FE80::1To: FF02::1 (All-nodes multicast) Prefix: 2001:DB8:AAAA:1:: Prefix-length: /64

NDP Router Solicitation From: FE80::50A5:8A35:A5BB:66 To: FF02::2 (All-routers multicast)


1

2

3

MAC: 00-21-9B-D9-C6-44

PC1

R1

Prefix: 2001:DB8:AAAA:1:: [EUI-64: Not used, Interface ID is randomly generated]Global Unicast Address: 2001:DB8:AAAA:1:50A5:8A35:A5BB:66E1Prefix-length: /64

2001:0DB8:AAAA:0001::/64

4 Default Router ListDefault Gateway: FE80::1

Link-local address: FE80::50A5:8A35:A5BB:66E1

Randomly generated Inter ID


Router Solicitation (RS) from PC1

Ethernet II, Src: 00:21:9b:d9:c6:44, Dst: 33:33:00:00:00:02

Internet Protocol Version 6 0110 .... = Version: 6 [Traffic class and Flowlabel not shown] Payload length: 16 Next header: ICMPv6 (0x3a) Hop limit: 255 Source: fe80::50a5:8a35:a5bb:66e1 Destination: ff02::2

Internet Control Message Protocol v6 Type: 133 (Router solicitation) Code: 0 Checksum: 0x3277 [correct] ICMPv6 Option (Source link-layer address) Type: Source link-layer address (1) Length: 8 Link-layer address: 00:21:9b:d9:c6:44

Link-local address of PC1All-routers multicast address

Router Solicitation message

MAC address of PC1 butRA sent as all-host multicast

Next header is an ICMPv6 header

All IPv6 routers multicast MAC address


R1(config)# ipv6 unicast-routing

R1# show ipv6 interface fastethernet 0/0FastEthernet0/0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::1 Global unicast address(es): 2001:DB8:AAAA:1::1, subnet is 2001:DB8:AAAA:1::/64 Joined group address(es): FF02::1 FF02::2 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.R1#

All-routers multicast group


Router Advertisement (RA) from Router R1

Ethernet II, Src: 00:03:6b:e9:d4:80, Dst: 33:33:00:00:00:01

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) Hop limit: 255 Source: fe80::1 Destination: ff02::1

Link-local address of R1. Added to the Default Router List and is the address hosts will use as their default gateway

All-nodes multicast group

Next Header is an ICMPv6 header

All IPv6 hosts multicast MAC address


Router Advertisement from Router R1 – some fields omitted

Internet Control Message Protocol v6 Type: 134 (Router advertisement) Code: 0 Cur hop limit: 64 Flags: 0x00 ICMPv6 Option (Source link-layer address) Type: Source link-layer address (1) Length: 8 Link-layer address: 00:03:6b:e9:d4:80 ICMPv6 Option (MTU) Type: MTU (5) Length: 8 MTU: 1500 ICMPv6 Option (Prefix information) Type: Prefix information (3) Length: 32 Prefix Length: 64 Prefix: 2001:db8:aaaa:1::

Recommended Hop Limit value for hosts M and O flags indicate that no information is available via DHCPv6

R1’s MAC address

MTU of the link.

Prefix-length (/64) to be used for autoconfiguration.Prefix of this network to be used for

autoconfiguration


M and O Flags

• M Flag: Managed Address Configuration flag• Tells the host whether to use the configuration information in this Router

Advertisement (SLAAC by default) or to get all of its information from a DHCPv6 server.

• O Flag: Other Configuration flag• When SLAAC is being used (using the RA), it tells the host whether more

information (like DNS) is available from a DHCPv6 server.

Internet Control Message Protocol v6 Type: 134 (Router advertisement) Code: 0 Cur hop limit: 64 Flags: 0x00 <output omitted for brevity?

M and O flags

Router Advertisement message


ipv6 unicast-routingR1DHCPv6 Server

NDP Router Advertisement

M Flag = 0 (Default)Use SLAAC, info in RA, prefix, etc.M Flag = 1Use DHCPv6 for everything

O Flag = 0 (Default)No additional information via DHCPv6O Flag = 1Additional information via DHCPv6 like DNS address

X

X

M FlagSLAAC or DHCPv6?

O FlagAdditional informationvia DHCPv6?

R1(config)# ipv6 managed-config-flag

R1(config)# ipv6 other-config-flag

Address Resolution


Neighbor Solicitation and Neighbor Advertisement • Two more protocols used with ICMPv6 Neighbor Discovery:

• Neighbor Solicitation• Neighbor Advertisement

• Used by a device to:• Request layer 2 address information from another device on the

same network• Provide this information to the requesting device.

• Part of three important processes:• Address resolution (like ARP in IPv4)• Duplicate Address Detection (DAD) • Neighbor Unreachability Detection (NUD)


ICMPv6 Neighbor Solicitation Message

ICMPv6 Neighbor Advertisement Message

If this is your Target IPv6 Address please send me your MAC address.

The Target IPv6 Address you are looking for belongs to me, here is my layer 2 (MAC) address.



3

4

2001:DB8:AAAA:1::100/64

PC1

R1



Target IPv6 Address: 2001:DB8:AAAA:1::200MAC address of PC1: 00:21:9B:D9:C6:44

PC2

2001:0DB8:AAAA:0001::/64




Target IPv6 Address: 2001:DB8:AAAA:1::200MAC address of PC2: 00:1B:24:04:A2:1E




2 5



IPv6 Addressing

What about that Solicited Node Multicast?

MulticastUnicast Anycast

Assigned Solicited Node

Global Unicast

UnspecifiedLoopback Embedded IPv4Link-Local Unique

Local

FF00::/8 FF02::1:FF00:0000/104

::/128::1/1282000::/3

3FFF::/3

FE80::/10FEBF::/10

FC00::/7

FDFF::/7

::/80


NIC: I will also listen for my MAC multicast addressesIP: I will also listen for my IP multicast addresses (Global and Link-local)

Global Unicast Address:Solicited Node

Multicast(Global):

MAC Unicast Address:Multicast (MAC):

2001:0DB8:AAAA:0001:0000:0000:0000:0200FF02::1:FF00:200

00-1B-24-04-A2-1E33-33-FF-00-02-00

PC-2

Why Solicited Node Addresses?• Devices also have solicited node multicast

addresses• Broadcasts are sent to all devices.• Devices must process all broadcasts at least to

layer 3.• Solicited Node Multicasts are only processed by

those devices with the matching last 24 bits (usually one device).

• If I know the IPv6 address but not the MAC address I can send it to a solicited node addresses instead of a broadcast to everyone…

Broadcasts


Interface ID

FF02 0000 0000 0000 0000 0001 FF

Global Routing Prefix104 bits

24 bits

PC2’s Global Unicast Address

PC2’s IPv6 Solicited-Node Multicast Address

Copy

PC2’s IPv6 Solicited-node multicast address: FF02::1:FF00:200PC2’s mapped solicited-node Ethernet multicast address : 33-33-FF-00-02-00

Subnet ID

2001:0DB8:AAAA 0001 0000:0000:00 00:0200

00:0200

FF-00-02-00

Copy

33-33Solicited-node Multicast address mapped to Ethernet destination MAC address


Neighbor Solicitation from PC1 (ARP Request)Ethernet II, Src: 00:21:9b:d9:c6:44, Dst: 33:33:ff:00:02:00

Internet Protocol Version 6 0110 .... = Version: 6 .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000 .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000 Payload length: 32 Next header: ICMPv6 (0x3a) Hop limit: 255 Source: 2001:db8:aaaa:1::100 Destination: ff02::1:ff00:200

Internet Control Message Protocol v6 Type: 135 (Neighbor solicitation) Code: 0 Checksum: 0xbbab [correct] Reserved: 0 (Should always be zero) Target: 2001:db8:aaaa:1::200 ICMPv6 Option (Source link-layer address) Type: Source link-layer address (1) Length: 8 Link-layer address: 00:21:9b:d9:c6:44

Global unicast address of PC1Solicited-node multicast address of PC2

Neighbor Solicitation message

Target IPv6 address, needing MAC address


MAC address of the sender, PC1

Mapped multicast address for PC2


Neighbor Advertisement from PC2 (ARP Reply)Ethernet II, Src: 00:1b:24:04:a2:1e, Dst: 00:21:9b:d9:c6:44


Internet Control Message Protocol v6 Type: 136 (Neighbor advertisement) Code: 0 Checksum: 0x1b4d [correct] Flags: 0x60000000 Target: 2001:db8:aaaa:1::200 ICMPv6 Option (Target link-layer address) Type: Target link-layer address (2) Length: 8 Link-layer address: 00:1b:24:04:a2:1e

1 1 0 – Router Flag = 1, Solicitation Flag = 1, Override Flag = 0


Unicast MAC address of PC2

Global unicast address of PC2Global unicast address of PC1

Neighbor Advertisement message

MAC address of the sender, PC2

IPv6 address of the sender, PC2



2001:DB8:AAAA:1::100/64

PC1

R1

PC2

2001:0DB8:AAAA:0001::/64





2 5

6ICMPv6 Echo RequestFrom Ethernet MAC address: 00-21-9B-D9-C6-44To: Ethernet MAC address: 00-1B-24-04-A2-1E


7

ICMPv6 Echo ReplyFrom: Ethernet MAC address: 00-1B-24-04-A2-1ETo: Ethernet MAC address: 00-21-9B-D9-C6-44


3

4Neighbor Solicitation

Neighbor Advertisement


ICMPv6 Echo Request from PC1Ethernet II, Src: 00:21:9b:d9:c6:44, Dst: 00:1b:24:04:a2:1e


Internet Control Message Protocol v6 Type: 128 (Echo (ping) request) Code: 0 (Should always be zero) Checksum: 0x7b37 [correct] ID: 0x0001 Sequence: 13 Data (32 bytes)


ICMPv6 Echo Reply from PC2Ethernet II, Src: 00:1b:24:04:a2:1e, Dst: 00:21:9b:d9:c6:44


Internet Control Message Protocol v6 Type: 129 (Echo (ping) reply) Code: 0 (Should always be zero) Checksum: 0x7a37 [correct] ID: 0x0001 Sequence: 13 Data (32 bytes)

Duplicate Address Detection


Duplicate Address Detection (DAD)

• Duplicate Address Detection (DAD) – Used to determine whether or not an address it wishes to use is already employed in use.

• Similar to a gratuitous ARP in IPv4.• With some exceptions, RFC 4861 recommends that DAD be performed

on every unicast address before it is assigned to an interface.


Duplicate Address Detection (DAD)For Link-local address


PC1

R1

Link-local address (Tentative) – Used Random Interface IDFE80::50A5:8A35:A5BB:66E1

2001:0DB8:AAAA:0001::/64

Neighbor Advertisement Message if it is in use…To: FF02::1 (All-nodes multicast)


2

1

3

Neighbor Solicitation MessageFrom Ethernet MAC address: 00-21-9B-D9-C6-44To Ethernet MAC address: 33-33-FF-BB-66-E1 (IPv6 Mapped Multicast)

From: :: (Unspecified source address – I don’t have an IPv6 address yet)To: FF02::1:FFBB:66E1 (Solicited Node Multicast)

Target IPv6 Address: FE80::50A5:8A35:A5BB:66E1

Neighbor Cache


Neighbor Cache• Similar to ARP tables in IPv4, the Neighbor Cache keeps track of the

reachability of neighbors: IPv6 address and MAC address mappings.• The Neighbor Cache entry can be in one of five states (RFC 4861):• 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.• Other three: (We will talk about all of these)

• INCOMPLETE—Address resolution is in progress, and the link-layer address is not yet known.

• DELAY—Neighbor is pending re-resolution, and traffic might flow to this neighbor.

• PROBE—Neighbor re-resolution is in progress, and traffic might flow to this neighbor.


Neighbor Cache (“ARP Cache”) for R1R1# show ipv6 neighborsIPv6 Address Age Link-layer Addr State InterfaceFE80::50A5:8A35:A5BB:66E1 16 0021.9bd9.c644 STALE Fa0/02001:db8:aaaa:1::100 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 msR1# show ipv6 neighborsIPv6 Address Age Link-layer Addr State InterfaceFE80::50A5:8A35:A5BB:66E1 16 0021.9bd9.c644 STALE Fa0/02001:DB8:AAAA:1::100 0 0021.9bd9.c644 REACH Fa0/0

R1#



Reachable








5 sec

NS sent andNA received

3 NS sent with no NA returned





To summarize…


Internet Control Message Protocol (ICMPv6) • Described in RFC 4443• Much more robust than ICMP for IPv4• Contains new functionality and

improvements. • General message similar to ICMP for IPv4• Also uses Type and Code fields like in

ICMPv4. • Two types of ICMPv6 messages

• Error messages • Informational messages


ICMPv6 Messages• The ICMPv6 error messages are:





ICMPv6 Messages• ICMPv6 informational messages used for Multicast Listener

Discovery (RFC 2710 ):• Multicast Listener Query• Multicast Listener Report• Multicast Listener Done

• ICMPv6 informational messages used by Neighbor Discovery (RFC 4861):• Router Solicitation Message• Router Advertisement Message• Neighbor Solicitation Message• Neighbor Advertisement Message• Redirect Message

Similar to IGMP (Internet Group Message Protocol) for IPv4.We won’t be covering these.

Most of our time will be spent on the first four of these.Redirect Message is similar to Redirect Messages for IPv4.



PC1R12001:0DB8:AAAA:0001::/64


2Neighbor Solicitation MessageFrom: :: (Unspecified source address)To: FF02::1:FFBB:66E1 (Solicited Node Multicast)Target IPv6 Address: FE80::50A5:8A35:A5BB:66E1

Link-local address (Tentative)

NDP Router Advertisement From: FE80::1 To: FF02::1 (All-nodes multicast)

NDP Router Solicitation From: FE80::50A5:8A35:A5BB:66E1 To: FF02::2 (All-routers multicast)

3

4

6 Neighbor Solicitation MessageFrom: :: (Unspecified source address)To: Solicited Node MulticastTarget IPv6 Address:

Addressing Information Added5

1Link-local address automatically created

DAD performed onLink-local address

Global unicast address created using SLAAC

DAD performed on global unicast address

Stateless Address Autconfiguration



3

4

2001:DB8:AAAA:1::100/64

PC1

R1



Target IPv6 Address: 2001:DB8:AAAA:1::200MAC address of PC1: 00:21:9B:D9:C6:44

PC2

2001:0DB8:AAAA:0001::/64




Target IPv6 Address: 2001:DB8:AAAA:1::200MAC address of PC2: 00:1B:24:04:A2:1E




2 5




Reachable








5 sec

NS sent andNA received







For more information•Web site: www.cabrillo.edu/~rgraziani•Username = cisco•Password = perlman

•Email: [email protected]

• At the end of these slides are some additional slides on the Destination Cache and configuring a router a a stateless DHCPv6 server.

IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6By Rick Graziani

Shameless plug!

mailto:[email protected]

Thank you!!!

Questions?



A quick word about the Destination Cache• Stores next-hop addresses for destinations to which traffic

has recently been sent. • Entries in the destination cache contain the:

• Destination IP address (either local or remote)• Previously resolved next-hop address• Path MTU for the destination.

• Generally applies to hosts.• Cisco command to display IPv6 MTU per destination cache:

• show ipv6 mtu


R1(config)# ipv6 dhcp pool cafe-1-poolR1(config-dhcp)# dns-server 2001:db8:cafe:2::d001R1(config-dhcp)# exit

R1(config)# interface fa 0/0R1(config-if)# ipv6 dhcp server cafe-1-poolR1(config-if)# ipv6 nd other-config-flagR1(config-if)# endR1#

DHCPv6 configuration pool commands

Enables DHCPv6 service on the interface.

Sets the Router Advertisement O flag (Other Configuration Flag) to 1

Stateless DHCPv6 configuration on R1


Verifying Router Advertisement Flags

R1# show ipv6 interface fastethernet 0/0FastEthernet0/0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::1 No Virtual link-local address(es): 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::5 FF02::6 FF02::1:2 FF02::1:FF00:1 MTU is 1500 bytes <output omitted for brevity> ND router advertisements are sent every 200 seconds ND router advertisements live for 1800 seconds ND advertised default router preference is Medium Hosts use stateless autoconfig for addresses. Hosts use DHCP to obtain other configuration.R1#

All_DHCP_Relay_Agents_and_Servers multicast group

Router Advertisement O Flag set to 1Router Advertisement M Flag set to 0


PC-1C> ipconfig /allEthernet adapter Local Area Connection:

Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Intel(R) 82567LM-3 Gigabit Network

Connection Physical Address. . . . . . . . . : B8-AC-6F-20-2A-90 DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IPv6 Address. . . . . . . . . . . :

2001:db8:cafe:1:e5ff:dd92:a512:19c6(Preferred) Link-local IPv6 Address . . . . . : fe80::e5ff:dd92:a512:19c6 Default Gateway . . . . . . . . . : fe80::1 DHCPv6 IAID . . . . . . . . . . . : 250629538 DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-15-EF-49-66-B8-AC-6F-20-2A-90 DNS Servers . . . . . . . . . . . : 2001:db8:cafe:2::d001

Documents

ICMPv6 & Neighbor Discovery Protocol: Learn It Rick Graziani CS/CIS Instructor Cabrillo College