IPv6 Basics – Notation, Address Types

IPv6 Workshop ManchesterSeptember 2013

Kateel Vijayanandakvijayan@cisco.comWim Verrydtwverrydt@cisco.com

Contents

IPv6 Basics

Notation

Address Types

Autoconfiguration

So How Big Is The IPv6 Address Space?

340,282,366,920,938,463,374,607,432,768,211,456

(IPv6 Address Space - 340 Trillion Trillion Trillion)

vs

4,294,967,296

(IPv4 Address Space - 4 Billion)

IPv4/IPv6 Technology Comparison

Service IPv4 IPv6

Addressing Range 32-bit, NAT 128-bit, Multiple Scopes

IP Provisioning DHCP SLAAC, Renumbering, DHCP

Security IPSec IPSec

Mobility Mobile IP Mobile IP with Direct Routing

Quality-of-Service Differentiated Service, Integrated Service

Differentiated Service, Integrated Service

Multicast IGMP/PIM/MBGP MLD/PIM/MBGP, Scope Identifier

Notation

The 8 groups of hexits are separated by colonsAddresses are conventionally written in lower case

IPv6 address = 128 bits(1 or 0)

IPv6 address = 32 hexits(0 - 9, a , b , c , d , e , f)

IPv6 address = 8 groups of 4 hexits 2001 : db8 : c001 : face : b00c : dead : 1cee : f001

Handling IPv6 Addresses

gggg:gggg:gggg: xxxx:xxxx:xxxx:xxxx

Global Routing Prefixn <= 48 bits

Subnet ID64 – n bits

Host

ssss:

2001:0000:0000:00A1: 0000:0000:0000:1E2A00A1:

Network Portion Interface ID

Global Unicast Identifier Example

2001:0:0:: ::1E2AA1

Full Format

Abbreviated Format

• Omit leading ZEROs in the HEX group

• Replace “empty” HEX groups by “0”

• Replace consecutive groups of ZEROs with “::”:: can be used only once in an address to avoid ambiguity

IPv6 Addressing Scheme

There is no broadcast nor network address

Global Unicast IPv6 addresses format defined in RFC 3587

CIDR principles usage:Prefix / Prefix length (or mask)

2001:660:3003::/482001:660:3003:2:a00:20ff:fe18:964c/64

Aggregation reduces routing table size

IPv6 Address TypesUnicast addresses

• Identifies an interface of an IPv6 node• Can be used as source and destination of a

packet• An interface can have multiple valid IPv6

addresses

Multicast addresses• Identifies a group of IPv6 addresses• Can only be used as the destination of a

transmission• An interface can belong to multiple multicast

addresses

Anycast addresses• Same address on multiple nodes• Packet to anycast address is delivered only to

nearest one• Packets are never sourced from an anycast

address

IPv6 Address Type Prefixes

Global Unicast assigments actually use 2000::/3 (001 prefix)Anycast addresses allocated from unicast prefixes

Address Type Binary Prefix IPv6 Notation

Unspecified 00…0 (128 bits) ::/128

Loopback 00…1 (128 bits) ::1/128

Multicast 1111 1111 FF00::/8

Link-Local Unicast 1111 1110 10 FE80::/10

ULA 1111 110 FC00::/7

Global Unicast (everything else)

IPv4-mapped 00…0:1111 1111:IPv4

::FFFF:IPv4/128

Site-Local Unicast (deprecated)

1111 1110 11 FEC0::/10

IPv4-compatible (deprecated)

00…0 (96 bits) ::IPv4/128

Current: n = 48: result: 16 bit subnet IDFixed high order bits of “001” => prefix of 2000::/3Example: 2001:db8:dead:beef:c001:babe:0000:aaaf

Global unicast addressesGlobal unicast addresses

001

64 Bitsn Bits 64-n Bits

Provider Site Host

Global Routing Prefix Subnet Interface ID

• First 10 bits are 1111 1110 10 thus prefix fe80::/10 • Scope is link local thus not forwarded off-link by routers• One per interface is always automatically configured when

IPv6 is enabled• Used for:

• Automatic address configuration• Default gateway on hosts and next-hops to routes• Routing protocol updates• Neighbor discovery

Link local unicast addressesLink local unicast addresses

“If you ping fe80::212:6bff:fe54:f99a (N1), what egress interface will router R use?” – see solution next slide

Link local reachability problemLink local reachability problem

ZoneID (or scopeID) Provides the extra routing information required Automatically assigned by the operating system Only locally significant

A full link-local address is written as : address%zoneID Examples of some full link-local addresses with zoneIDs:

[Windows] ping fe80::245:bcff:fe47:1530%11 [Linux] ping6 fe80::245:bcff:fe47:1530%eth0

ZoneIDs (scopeIDs) – solving Link ambiguityZoneIDs (scopeIDs) – solving Link ambiguity

IPv6 over Ethernet

IPv6 uses Ethernet Protocol ID (0x86DD)

IPv4 uses Ethernet Protocol ID (0x0800)

0x0800

0x86DD IPv6 Header and PayloadDest MAC Source MAC

IPv6 Header and PayloadDest MAC Source MAC

IPv6 Interface Identifier (EUI-64 format)

FF FE

00 90 27 17 FC 0F

000000U0 where U=1 = Unique

0 = Not UniqueU = 1

00 90 27 17 FC 0F

FF FE00 90 27 17 FC 0F

FF FE02 90 27 17 FC 0F

MAC Address

• EUI-64 format is used by stateless auto-configuration• To make sure that the chosen address is from a unique Ethernet MAC address, the

universal/local (“u” bit) is set to 1 for global scope and 0 for local scope• Cisco devices ‘bit-flip’ the 7th bit (RFC 3513)

U bit in a MAC address (U=0: globally unique, U=1:locally administered) and EUI address have opposite meaning

IPv6 Multicast Address Format (RFC 4291)

An IPv6 multicast address has the prefix FF00::/8 (1111 1111)• Second octet defines lifetime and scope

Flags

R = 0R = 1

No embedded RPEmbedded RP

P = 0P = 1

Not based on unicastBased on unicast

T = 0T = 1

Permanent address (IANA assigned)Temporary address (local assigned)

Scope

1 Node

2 Link

3 Subnet

4 Admin

5 Site

8 Organisation

E Global

112 Bits8Bits 4 Bits

0 R P T Group ID (Variable Format)1111 1111 Scope

4 Bits

Well Known Multicast Addresses

Address Scope Meaning

FF01::1 Node-Local All Nodes

FF01::2 Node-Local All Routers

FF02::1 Link-Local All Nodes

FF02::2 Link-Local All Routers

FF02::5 Link-Local OSPFv3 Routers

FF02::6 Link-Local OSPFv3 DR Routers

FF02::1:FFXX:XXXX Link-Local Solicited-Node

“02” means that this is a permanent address (t = 0) and has link scope (2)

http://www.iana.org/assignments/ipv6-multicast-addresses

IPv4 and IPv6 Header Comparison

Fragment Offset

Flags

Total LengthType of ServiceIHL

PaddingOptions

Destination Address

Source Address

Header ChecksumProtocolTime to Live

Identification

Version

IPv4 Header

Next Header

Hop Limit

Flow LabelTraffic Class

Destination Address

Source Address

Payload Length

IPv6 Header

Field’s Name Kept from IPv4 to IPv6

Fields Not Kept in IPv6

Name and Position Changed in IPv6

New Field in IPv6

Leg

end

Version

20 b

ytes

40 b

ytes

Extension Headers

Extension Headers Are Daisy Chained

Class Flow6 Hop

Destination

VLen

Source

Upper Layer TCP Header

Payload

Class Flow43 Hop

Destination

VLen

Source

Upper Layer UDP Header

Payload

Routing Header17

Class Flow43 Hop

Destination

VLen

Source

Upper Layer TCP Header

Payload

Routing Header60

Destination Options6

IPv6 Extension Headers – order is important

IPv6

Hop by hop (0)

Destination

Routing (43)

Fragmentation (44)

Authentication (51)

Security

Destination (60)

Upper Layer

Processed by every router

Processed by routers listed in Routing extension

List of routers to cross

Processed by the destination

After reassembling the packet

Cipher the content of the remaining information

Processed only by the destination

RFC 2460

IPv6 ext. header processing

IPv6 extensions (except Hop-by-Hop) are processed only by the destination.

A

B

A -> R1

B

A -> B

R1R1

R1

Fragmentation in IPv6

• Fragmentation is left to end devices in IPv6• Routers do not perform fragmentation

• Fragment header used when an end node has to send a packet larger than the path MTU

• Minimum MTU for IPv6 is 1280 bytes• All links MUST support it

Next Header Reserved

Fragment Data

Fragment Offset M

44

IPv6 basic header

Fragment Header (44)

Identification

00

Next Header

Fundamentals on Neighbor Discovery RFC 4861

Defined in RFC 4861, “Neighbor Discovery for IP Version 6 (IPv6)” and RFC 4862 (“IPv6 Stateless Address Autoconfiguration”)

Used for:• Router discovery • Autoconfiguration of addresses (SLAAC)• IPv6 address resolution (replaces ARP)• Neighbor Reachability (NUD)• Duplicate Address Detection (DAD)• Redirection

Operates above ICMPv6• Rely heavily on multicast (including L2-multicast)

Works with icmp messages and messages “options”

36

Neighbor Discovery Messages (ND) RFC 4861ND uses ICMPv6 messages

• Originated from node on link local with a hop limit of 255• Receivers checks hop limit is still 255 (has not passed a router)

Consists of IPv6 header, ICMPv6 header, neighbor discovery header, and neighbor discovery options

Five neighbor discovery messages

Message Purpose ICMP Code

Sender Target

Router Solicitation (RS)

Prompt routers to send RA 133 Nodes All routers

Router Advertisement (RA)

Advertise default router, prefixesOperational parameters

134 Routers Sender of RSAll routers

Neighbor Solicitation (NS)

Request link-layer of target 135 Node Solicited NodeTarget Node

Neighbor Advertisement (NA)

Response to NS (solicited)Advertise link-layer address change (Unsolicited)

136 Nodes

Redirect Inform hosts of a better first hop 137 Routers

37

Router Solicitation and Advertisement(RS & RA) – Stateless Autoconfiguration (aka SLAAC)

Router solicitations (RS) are sent by booting nodes to request RAs for configuring the interfaces

Routers send periodic Router Advertisements (RA) to the all-nodes multicast address. Default is 200 seconds ipv6 nd ra-interval

Solicited RA’s are unicast to the requesting client

RouterSolicitation

ICMP Type 133

IPv6 Source Link Local of A(FE80::)

IPv6 Destination All Routers Multicast (FF02::2)

Query Please send me RA

RouterAdvertisement

ICMP Type 134

IPv6 Source Link Local of R(FE80::)

IPv6 Destination All Nodes Multicast (FF02::1)

Data Options, subnet prefix, lifetime, autoconfig-flag, MTU

RS RA

A R

38

IPv6 Neighbor Solicitation & Advertisement

A B

NeighbourSolicitation

ICMP Type 135

IPv6 Source A Unicast

IPv6 Destination

B Solicited Node Multicast

Data FE80:: address of A

Query What is B link layer address?

NeighbourAdvertisement

ICMP Type 136

IPv6 Source B Unicast

IPv6 Destination A Unicast

Data FE80:: address of B

NS NA

Security Implications ??

ND Guard, DAD, DHCPv6 and ICMPv6 guards

Similar function toARP in IPv4 without

broadcasts

39

Conclusion• New packets headers in IPv6

• Different notation, compacting makes life easier

• Several types of IPv6 addresses to be considered

Questions