IPv6 Operations

© 2006 Cisco Systems, Inc. All rights reserved. IP6FD v2.0—2-1

IPv6 Operations

Defining and Configuring Neighbor Discovery


ICMPv6

ICMPv6 is similar to ICMPv4:• Provides diagnostic and error messages• Used for path MTU discovery

ICMPv6 Type ICMPv6 Code

ICMPv6 Data

Checksum

IPv6 Basic Header

ICMPv6 Packet

Next Header = 58 ICMPv6 Packet

ICMPv6 Packet


MTU = 1300

Path MTU Discovery

MTU = 1500

MTU = 1500

MTU = 1400

Packet with MTU = 1500

ICMP error: packet too big Use MTU = 1400


ICMP error: packet too big Use MTU = 1300


Path MTU = 1300

Source Destination


Maximum Transmission Unit

• IPv4 – MTU >= 68 octets

• IPv6 – MTU >= 1280 octets– Path MTU used

Frame Header Frame TrailerIPv6 Packet

Minimum MTU = 1280 Octets

Link-Layer Frame


IPv6 over Data Link Layers

IPv6 is defined for most data link layers:• Ethernet• PPP• FDDI• Token Ring• HDLC• Nonbroadcast multiaccess • ATM• Frame Relay• IEEE 1394


IPv6 over Ethernet

IPv6 has a specific Ethernet protocol ID that is different from the protocol ID in IPv4.

Destination Ethernet Address

IPv6 Header and Payload0x86DDSource

Ethernet Address


000000X0

02

00 90 27

00 90 27

90 27

17 FC 0F

17 FC 0F

FF FE

Modified EUI-64 Format

A modified EUI-64 address is formed by inserting "FFFE" and “complementing” a bit identifying the uniqueness of the MAC address.

where X =1 = universally unique0 = locally uniqueX = 1

Ethernet MAC Address (48 Bits)

64-Bit Version

U/L Bit

Modified EUI-64 Address

00 90 27

17 FC 0F

17 FC 0FFF FE

FF FE


Neighbor Discovery

• Neighbor discovery:– Queries for duplicate address detection– Determines the link layer address of a neighbor on the

same link– Finds neighbor routers on link

• Achieved by using ICMPv6 with IPv6 multicast


Solicited-Node Multicast Address

Solicited-node address:• Multicast address with a link-local scope• Formed by a prefix and the rightmost 24 bits of every unicast

and anycast address

Prefix

0 Lower 24

Interface ID

FF02

128 Bits

FF

24 Bits

IPv6 Address

Solicited-Node Multicast Address0001


FF02 0000 0000 0000 0000 0001

33 33

FF17 FC0F

17 FC 0FFF

Multicast Mapping over Ethernet

IPv6 Solicited-Node Multicast Address

Corresponding Ethernet Address

Multicast Prefix for Ethernet

Multicast

2001 0DB8 1001 000F 02C0 10FF FC0FIPv6 Address FE 17


Duplicate Address Detection

ICMP type = 135 Src = 0 (::) Dst = solicited-node multicast of A Data = link-layer address of A Query = What is your link address?

DAD uses neighbor solicitation to verify the existence of an address to be configured.

BA


ICMP type = 136 Src = B Dst = A Data = link-layer address of B

ICMP type = 135 Src = A Dst = solicited-node multicast of B Data = link-layer address of A Query = What is your link address?

A and B can now exchange packets on this link.

Neighbor Discovery: Neighbor Solicitation

BA


Neighbor Discovery: Neighbor Solicitation (Cont.)

Neighbor Advertisement Message• R: router flag, indicates sender is a router• S: solicited flag, indicates message sent in response

to a neighbor solicitation• O: override flag, indicates advertisement should override

existing neighbor cache entry


Neighbor Discovery: Autoconfiguration

Autoconfiguration• Stateless

– Uses neighbor discovery router advertisements• Stateful

– Uses DHCPv6 service


Routers send periodic router advertisements to the all-nodes multicast address.

Router advertisement packet definitions:ICMP type = 134Src = router link-local addressDst = all-nodes multicast addressData = options, prefix, lifetime, autoconfiguration flag

Router Advertisement

Neighbor Discovery: Router Advertisements

RouterAdvertisement


Neighbor Discovery Parameters

Router advertisements:• Default router• IPv6 network prefix• Lifetime of advertisement

Autoconfiguring IPv6 Hosts


Neighbor Discovery Parameters (Cont.)

Router advertisements:• Default router• IPv6 network prefix• Lifetime of advertisement



Neighbor Discovery: Router Solicitations

At boot time, nodes send router solicitations to promptly receive router advertisements.

Router solicitation packet definitions:ICMP type = 133Src = unspecified addressDst = all-routers multicast address

RouterAdvertisement

Router Solicitation


Stateless Autoconfiguration

Router solicitations are sent by booting nodes to request router advertisement for configuring the interfaces.

1. Router Solicitation:ICMP type = 133Src = ::Dst = all-routers multicastaddressQuery = Please send router advertisement

2. Routeradvertisement

1. Routersolicitation

2. Router Advertisement:ICMP type = 134Src = router link-local addressDst = all-nodes multicast addressData = options, prefix, lifetime, autoconfiguration flag

2. Routeradvertisement


Router advertisement packet definitions:ICMP type = 134Src = Router link-local addressDst = All-nodes multicast addressData = Two prefixes:

Current prefix (to be deprecated) with short lifetimeNew prefix (to be used) with normal lifetime

Renumbering

Renumbering is achieved by modifying the router advertisement to announce the old prefix with a short lifetime and the new prefix.

RouterAdvertisement


Value of Autoconfiguration

• IPv6 address autoconfiguration enables “plug-and-play.”• Nodes may be deployed without a DHCPv6 server:

– Mobile devices (phones, PDAs, autos)– Home electronics (TVs, DVRs, appliances)– Field telemetry (oil pipeline gauges)

• Autoconfiguration enables massive deployment (millions) of IPv6 nodes.


ipv6 nd prefix <prefix> | default [ [<valid-lifetime> <preferred-lifetime>] | [at <valid-date> <preferred-date>] [off-link] [no-autoconfig] ]

router(config-if)#

• Used to modify prefix advertisement parameters on an interface from their default values.

Cisco IOS Neighbor Discovery Command Syntax


LAN2: 2001:db8:c18:2::/64

LAN1: 2001:db8:c18:1::/64


Ethernet1

Ethernet0

Ethernet0

interface Ethernet0 ipv6 address 2001:db8:c18:1::2/64 ipv6 nd prefix 2001:db8:c18:1::/64 2000 1800



Router2

Router1

Cisco IOS Command for Overriding the Neighbor Discovery Defaults


IPv6 Internet


LAN1: 2001:db8:c18:1::/64

LAN2: 2001:db8:c18:2::/64

Ethernet0

Ethernet1

Ethernet0

interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/64 2000 1800



Router2

Router1

Cisco IOS Command for Overriding the Neighbor Discovery Defaults (Cont.)



IPv6 Internet


LAN1: 2001:db8:c18:1::/64

LAN2: 2001:db8:c18:2::/64

Ethernet0

Ethernet1

Ethernet0

interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/64 43200 43200 ipv6 nd ra lifetime 100



Router2

Router1

Cisco IOS Neighbor Discovery Lifetimes



IPv6 Internet


Network Prefix: 2001:db8:c18:1::/64


Host Configuration:Autoconfiguring IPv6 Hosts preferred address 2001:db8:c18:1:260:8ff:fede:8fbe

Router Configuration before Renumbering:

Router Advertisements

Cisco IOS Network Prefix Renumbering Scenario


interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/64 43200 0 ipv6 nd prefix 2001:db8:c18:2::/64 43200 43200

New Network Prefix: 2001:db8:c18:2::/64Deprecated Prefix: 2001:db8:c18:1::/64

Host Configuration:


deprecated address 2001:db8:c18:1:260:8ff:fede:8fbepreferred address 2001:db8:c18:2:260:8ff:fede:8fbe

Router Configuration after Renumbering:

Router Advertisements

interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/64 at Jul 31 2002 23:59 Jul 1 2002 23:59 ipv6 nd prefix 2001:sb8:c18:2::/64 43200 43200

Cisco IOS Network Prefix Renumbering Scenario (Cont.)

or:


Summary

• ICMP messages are used for many IPv6 functions, including path MTU discovery, neighbor discovery, and router discovery. ICMPv6 is an integral part of IPv6 but looks similar to a Layer 4 protocol, much like TCP or UDP.

• Path MTU is performed by nodes in an effort to determine the largest packet size they can send to a given destination. It is based on a process of sending large packets and listening for ICMPv6 error messages.

• Neighbor discovery is a critical process that allows neighbors to determine the link-layer address associated with a given IPv6 address. It also allows hosts to receive prefix information to configure a global-scope address and find the default router.

• Before a node can use an address, it must test it for uniqueness on the link. DAD is a process by which a node with a "tentative" address that it would like to use determines if that address is already in use.

• Autoconfiguration provides a type of network “plug-and-play,” easily supporting millions of transient nodes and enabling a network environment with support for mobile phones, field sensors, and home appliances.

• Cisco routers are IPv6-ready and are configured for IPv6 functions on a global and per-interface basis, depending on the function being enabled.


Documents

IPv6 Operations