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IPv6: An Introduction
Dheeraj Sanghi
Department of Computer Science and Engineering
Indian Institute of Technology Kanpur
http://www.cse.iitk.ac.in/users/dheeraj
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Outline
Problems with IPv4
Basic IPv6 Protocol
IPv6 features
Auto-configuration, QoS, Security, Mobility
Transition Plans
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Internet Protocol
Transports a datagram from source host to destination,possibly via several intermediate nodes (routers)
Service is: Unreliable:Losses, duplicates, out-of-order delivery
Best effort:Packets not discarded capriciously, deliveryfailure not necessarily reported
Connectionless:Each packet is treated independently
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IP Datagram Header
VERS HLEN TOS TOTAL LENGTH
IDENTIFICATION FLAG FRAGMENT OFFSET
TTL PROTOCOL CHECKSUM
SOURCE ADDRESS
DESTINATION ADDRESS
OPTIONS (if any) + PADDING
0 4 8 16 19 31
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Problems with IPv4: Limited Address Space
IPv4 has 32 bit addresses.
Flat addressing (only netid + hostid with fixed
boundaries) Results in inefficient use of address space.
Class B addresses are almost over.
Addresses will exhaust in the next 5 years.
IPv4 is victim of its own success.
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Problems with IPv4: Routing Table Explosion
IP does not permit route aggregation(limited supernetting possible with new routers)
Mostly only class C addresses remain
Number of networks is increasing very fast
(number of routes to be advertised goes up)
Very high routing overhead
lot more memory needed for routing table
lot more bandwidth to pass routing information
lot more processing needed to compute routes
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Problems with IPv4: Header Limitations
Maximum header length is 60 octets.(Restricts options)
Maximum packet length is 64K octets.(Do we need more than that ?)
ID for fragments is 16 bits. Repeats every 65537th packet.(Will two packets in the network have same ID?)
Variable size header.(Slower processing at routers.)
No ordering of options.(All routers need to look at all options.)
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Problems with IPv4: Other Limitations
Lack of quality-of-service support.
Only an 8-bit ToS field, which is hardly used.
Problem for multimedia services.
No support for security at IP layer. Mobility support is limited.
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IP Address Extension
Strict monitoring of IP address assignment
Private IP addresses for intranets
Only class C or a part of class C to an organization
Encourage use of proxy services
Application level proxies
Network Address Translation (NAT)
Remaining class A addresses may use CIDR
Reserved addresses may be assigned
But these will only postpone address exhaustion.
They do not address problems like QoS, mobility, security.
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IPng Criteria
At least 109 networks, 1012 end-systems
Datagram service (best effort delivery)
Independent of physical layer technologies
Robust (routing) in presence of failures Flexible topology (e.g., dual-homed nets)
Better routing structures (e.g., aggregation)
High performance (fast switching)
Support for multicasting
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IPng Criteria
Support for mobile nodes
Support for quality-of-service
Provide security at IP layer
Extensible Auto-configuration (plug-and--play)
Straight-forward transition plan from IPv4
Minimal changes to upper layer protocols
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IPv6: Distinctive Features
Header format simplification
Expanded routing and addressing capabilities
Improved support for extensions and options
Flow labeling (for QoS) capability Auto-configuration and Neighbour discovery
Authentication and privacy capabilities
Simple transition from IPv4
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IPv6 Header Format
Traffic Class Flow LabelVers
Payload Length Next Header Hop Limit
Source Address
Destination Address
0 4 12 16 24 31
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IPv6 Header Fields
Version number (4-bit field)The value is always 6.
Flow label (20-bit field)
Used to label packets requesting special handling by
routers. Traffic class (8-bit field)
Used to mark classes of traffic.
Payload length (16-bit field)
Length of the packet following the IPv6 header, in octets. Next header (8-bit field)
The type of header immediately following the IPv6 header.
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IPv6 Header Fields
Hop limit (8-bit field)Decremented by 1 by each node that forwards the packet.
Packet discarded if hop limit is decremented to zero.
Source Address (128-bit field)
An address of the initial sender of the packet. Destination Address (128-bit field)
An address of the intended recipient of the packet. Maynot be the ultimate recipient, if Routing Header is present.
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Header Changes from IPv4
Longer address - 32 bits 128 bits
Fragmentation field moved to separate header
Header checksum removed
Header length removed (fixed length header) Length field excludes IPv6 header
Time to live Hop limit
Protocol Next header
64-bit field alignment TOS replaced by flow label, traffic class
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Extension Headers
Less used functions moved to extension headers.
Only present when needed.
Processed only by node identified in IPv6 destination field.
=> much lower overhead than IPv4 options
Exception: Hop-by-Hop option header
Eliminated IPv4s 40-byte limit on options
Currently defined extension headers: Hop-by-hop,Routing, Fragment, Authentication, Privacy, End-to-end.
Order of extension headers in a packet is defined.
Headers are aligned on 8-byte boundaries.
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Address Types
Unicast Address for a single interface.
Multicast Identifier for a set of interfaces.
Packet is sent to allthese interfaces.
Anycast Identifier for a set of interfaces.Packet is sent to the nearestone.
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Text Representation of Addresses
HEX in blocks of 16 bits
BC84 : 25C2 : 0000 : 0000 : 0000 : 55AB : 5521 : 0018
leading zero suppression
BC84 : 25C2 : 0 : 0 :55AB : 5521 : 18
Compressed format removes strings of0s
BC84 : 25C2 :: 55AB : 5521 : 18
:: can appear only once in an address.
can also be used to compress leading or trailing 0s Mixed Notation (X:X:X:X:X:X:d.d.d.d)
e.g.,::144.16.162.21
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IPv6 Addresses
128-bit addresses
Multiple addresses can be assigned to an interface
Provider-based hierarchy to be used in the beginning
Addresses should have 64-bit interface IDs in EUI-64format
Following special addresses are defined :
IPv4-mapped
IPv4-compatible link-local
site-local
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Unicast Addresses Examples
Global Aggregate Address
Link local address
Site-local address
FP TLA NLA
3 13 32
SLA
64 bits
Interface ID
1111111010
10 bits
0
54 bits
Interface ID
64 bits
Public Topology Site
Topology
Interface Identifier
1111111011 0 Interface IDsubnet ID
10 bits 38 bits 16 bits 64 bits
16
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Multicast Address
Flags 000T 3 bits reserved
T= 0 permanent
T= 1 transient
Scope 2 link-local5 site-local8 org-localE global
Permanent groups are formed independent of scope.
11111111 flags scope Group ID
8 bits 4 4 112 bits
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IPv6 Routing
Hierarchical addresses are to be used. Initially only provider-based hierarchy will be used.
Longest prefix match routing to be used.
(Same as IPv4 routing under CIDR.)
OSPF, RIP, IDRP, ISIS, etc., will continue as is
(except 128-bit addresses).
Easy renumbering should be possible.
Provider selection possible with anycastgroups.
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QoS Capabilities
Protocol aids QoS support, not provide it.
Flow labels
To identify packets needing same quality-of-service
20-bit label decided by source Flow classifier: Flow label + Source/Destination addresses
Zero if no special requirement
Uniformly distributed between 1 and FFFFFF
Traffic class 8-bit value Routers allowed to modify this field
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IPv6: Security Issues
Provision for
Authentication header
Guarantees authenticity and integrity of data
Encryption header
Ensures confidentiality and privacy
Encryption modes:
Transport mode
Tunnel mode
Independent of key management algorithm.
Security implementation is mandatoryrequirement in IPv6.
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Mobility Support in IPv6
Mobile computers are becoming commonplace.
Mobile IPv6 allows a node to move from one link toanother without changing the address.
Movement can be heterogeneous, i.e., node can movefrom an Ethernet link to a cellular packet network.
Mobility support in IPv6 is more efficient than mobilitysupport in IPv4.
There are also proposals for supporting micro-mobility.
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Neighbour Discovery
Router Discovery - determines set of routers on the link. Prefix Discovery - set of on-link address prefixes.
Parameter Discovery - to learn link parameters such aslink MTU, or internet parameters like hop limit, etc.
Address Auto-configuration - address prefixes that canbe used for automatically configuring interface address.
Address resolution - IP to link-layer address mapping.
Duplicate Address Detection.
Route Redirect - inform of a better first hop node toreach a particular destination.
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Neighbour Discovery Operation
Based on ICMPv6 messages Router Solicitation (RS)
Router Advertisement (RA)
Neighbour Solicitation (NS)
Neighbour Advertisement (NA) Redirect
Router Solicitation
sent when an interface becomes enabled, hostsrequest routers to send RA immediately.
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Neighbour Discovery Operation (contd..)
Router advertisement
Sent by routers periodically or in response to RS.
Hosts build a set of default routers based on thisinformation.
Provides information for address auto-configuration, set of on-link prefixes etc.
Supplies internet/subnet parameters, like MTU,and hop limit.
Includes routers link-layer address.
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Neighbour Discovery Operation (contd..)
Neighbour Solicitation
To request link-layer address of neighbour
Also used for Duplicate Address Detection
Neighbour Advertisement
Sent in response to NS
May be sent without solicitation to announce changein link-layer address
Redirect - used to inform hosts of a better first hopfor a destination.
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Additional Features
Anycast Addresses Multiple nodes on link may have this address
All those nodes will respond to an NS message.
Host will get multiple NA messages, but shouldaccept only one.
The messages should be tagged as non-override.
Proxy advertisements
Router may send NA on behalf of others.
Useful for mobile nodes who have moved.
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Address Auto-configuration
The problem
System bootstrap (plug and play) Address renumbering
Addressing Possibilities
Manual Address configured by handAutonomous Host creates address with no external
interaction (e.g., link local)
Semi-autonomous Host creates address by combining a prioriinformation and some external information.
Stateless Server Host queries a server, and gets an address.Server does not maintain a state.
Stateful Server Host queries a server, and gets an address.Server maintains a state.
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Auto-configuration in IPv6
Link-local prefix concatenated with 64-bit MAC address.
(Autonomous mode)
Prefix advertised by router concatenated with 64-bit MACaddress. (Semi-autonomous mode.)
DHCPng (for server modes)
Can provide a permanent address (stateless mode)
Provide an address from a group of addresses, and keep trackof this allocation (stateful mode)
Can provide additional network specific information.
Can register nodes in DNS.
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Address Renumbering
To migrate to a new address
change of provider change in network architecture
Methods
router adds a new prefix in RA, and informs that the old
prefix is no longer valid. When DHCP lease runs out, assign a new address to node.
DHCPng can ask nodes to release their addresses.
Requires DNS update. DHCPng can update DNS for clients.
Existing conversations may continue if the old addresscontinues to be valid for some time.
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Upper Layer Issues
Minor changes in TCP
Maximum segment size should be based on Path MTU.
The packet size computation should take into account largersize of IP header(s).
Pseudo-header for checksum is different.
UDP checksum computation is now mandatory.
Most application protocol specifications areindependent of TCP/IP - hence no change.
FTP protocol exchanges IPv4 addresses - hence needsto be changed.
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The pseudo-header is changed in checksum
computation: Address are 128 bits.
Payload length is 32 bits.
Payload length is not copied from IPv6 header.
(Extension headers should not be counted.) Next header field of last extension header is used in place
of protocol.
UDP packets must also have checksum.
(Since no IP checksum now.)
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Changes in Other Protocols
ICMPv6
Rate limiting feature added
Timer based
Bandwidth based
IGMP, ARP merged
Larger part of offending packet is included
DNS
AAAA type for IPv6 addresses
A6 type: recursive definition of IP address
Queries that do additional section processing are redefinedto do processing for both A and AAAA type records
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Socket API
Sockets interface the de facto standard API for TCP/IPApplications.
Need to change Socket API in order to reflect the increasedaddress length in IPv6.
Also need to make new features like flow label, visible toapplications.
A few new library routines
Complete source and binary compatibility with original API.
One can have some sockets using IPv4 and others usingIPv6.
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Transition to IPv6: Design Goal
No flagday. Incremental upgrade and deployment.
Minimum upgrade dependencies.
Interoperability of IPv4 and IPv6 nodes.
Let sites transition at their own pace.
Basic migration tools
Dual stack and tunneling
Translation
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Transition Mechanisms: Dual Stack
New nodes support both IPv4 and IPv6.
Upgrading from IPv4 to v4/v6 does not break anything. Same transport layer and application above both.
Provides complete interoperability with IPv4 nodes.
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Transition Mechanism: Tunnels
Tunnel IPv6 packets across IPv4 topology.
Configured tunnels:
Explicitly configured tunnel endpoints.
Router to router, host to router.
Automatic tunnels:
Automatic address resolution using embedded IPv4address (like IPv4-compatible address).
Host to host, router to host
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Transition mechanism: Translation
This will allow communication between IPv6 onlyhosts and IPv4 only hosts.
A typical translator consists of two components:
translation between IPv4 and IPv6 packets. Address mapping between IPv4 and IPv6
For translation, three technologies are available:
header conversion
transport relay application proxy
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NAT-PT
Combination of Network Address Translation(NAT) and Protocol Translation (PT)
Meant for communication between IPv6-only andIPv4-only nodes.
No change is needed on the IPv6-only nodes.
But translation is not stateless.
Hence, single point of failure.
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NAPT-PT
Network Address Port Translation + Protocol Translation
In addition to changing IP address, changes the portnumber also in the transport layer header.
It will allow IPv6 nodes to communicate with IPv4 nodestransparently using a single IPv4 address.
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Stateless IP-ICMP Translation (SIIT)
SIIT also translates between IPv4 and IPv6 headers.
Stateless: Translator does not keep address mapping.
There has to be a translator on every path, notnecessarily on all physical links.
Uses IPv4-translatable addresses.
Assumes that there is an IPv4 address pool of addressesfor the subnet.
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Issues in Translation
PMTU discovery is optional on IPv4 network.
Fragmentation is difficult to handle.
Security Associations may not be transparent.
Options may not be translatable.
UDP checksum is optional over IPv4.
Some ICMP messages are different.
Connections can only start from IPv6 node.
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Transition Plan for Internet
Maintain complete V4 routing till addresses last.
Upgrade V4 routers to dual stack.
Incrementally build up V6 backbone routing system.
Use v6-over-v4 tunnels to construct 6bone. Grow like Mbone (multicast backbone).
De-activate tunnels as soon as underlying pathupgraded to V6.
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Transition Options for User Sites
Incrementally upgrade V4 hosts to dual V4/V6 Use IPv4-compatible addresses with existing IPv4address assignments
Host-to-host automatic tunneling over IPv4
Upgrade routers to IPv6.
Hosts may require native IPv6 addresses
DNS upgrade is needed before hosts get IPv6addresses
Connect IPv6 router to an IPv6-enabled ISP.
Install translators like NAT-PT or SIIT.
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Thank You