IPv6: An Introduction

1. IPv6: An Introduction Dheeraj Sanghi Department of Computer Science and Engineering Indian Institute of Technology Kanpur dheeraj@iitk.ac.in http://www.cse.iitk.ac.in/users/dheeraj

2. Outline • Problems with IPv4 • Basic IPv6 Protocol • IPv6 features • Auto-configuration, QoS, Security, Mobility • Transition Plans IIT Kanpur

3. 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, delivery failure not necessarily reported • Connectionless: Each packet is treated independently IIT Kanpur

4. IP Datagram Header 31 0 4 8 16 19 TOTAL LENGTH HLEN TOS VERS IDENTIFICATION FRAGMENT OFFSET FLAG TTL PROTOCOL CHECKSUM SOURCE ADDRESS DESTINATION ADDRESS OPTIONS (if any) + PADDING IIT Kanpur

5. 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. IIT Kanpur

6. 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 IIT Kanpur

7. 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.) IIT Kanpur

8. 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. IIT Kanpur

9. 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. IIT Kanpur

10. 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 IIT Kanpur

11. 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 IIT Kanpur

12. 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 IIT Kanpur

13. IPv6 Header Format 0 4 12 16 24 31 Traffic Class Flow Label Vers Next Header Payload Length Hop Limit Source Address Destination Address IIT Kanpur

14. 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. IIT Kanpur

15. 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. May not be the ultimate recipient, if Routing Header is present. IIT Kanpur

16. 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 IIT Kanpur

17. 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 IPv4’s 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. IIT Kanpur

18. Address Types Unicast Address for a single interface. Multicast Identifier for a set of interfaces. Packet is sent to all these interfaces. Anycast Identifier for a set of interfaces. Packet is sent to the nearest one. IIT Kanpur

19. 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 of 0s 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 IIT Kanpur

20. 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-64 format • Following special addresses are defined : • IPv4-mapped • IPv4-compatible • link-local • site-local IIT Kanpur

21. Global Aggregate Address Link local address Site-local address Unicast Addresses Examples 3 13 32 16 64 bits FP TLA NLA SLA Interface ID Interface Identifier Public Topology Site Topology 10 bits 54 bits 64 bits 0 Interface ID 1111111010 64 bits 10 bits 38 bits 16 bits 1111111011 0 subnet ID Interface ID IIT Kanpur

22. Multicast Address 8 bits 4 4 112 bits flags scope Flags 000T 3 bits reserved T= 0 permanent T= 1 transient Scope 2 link-local 5 site-local 8 org-local E global Permanent groups are formed independent of scope. Group ID 11111111 IIT Kanpur

23. 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 anycast groups. IIT Kanpur

24. 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 IIT Kanpur

25. 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 mandatory requirement in IPv6. IIT Kanpur

26. Mobility Support in IPv6 • Mobile computers are becoming commonplace. • Mobile IPv6 allows a node to move from one link to another without changing the address. • Movement can be heterogeneous, i.e., node can move from an Ethernet link to a cellular packet network. • Mobility support in IPv6 is more efficient than mobility support in IPv4. • There are also proposals for supporting micro-mobility. IIT Kanpur

27. 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 as link MTU, or internet parameters like hop limit, etc. • Address Auto-configuration - address prefixes that can be 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 to reach a particular destination. IIT Kanpur

28. 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, hosts request routers to send RA immediately. IIT Kanpur

29. Neighbour Discovery Operation (contd..) • Router advertisement • Sent by routers periodically or in response to RS. • Hosts build a set of default routers based on this information. • Provides information for address auto-configuration, set of on-link prefixes etc. • Supplies internet/subnet parameters, like MTU, and hop limit. • Includes router’s link-layer address. IIT Kanpur

30. 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 change in link-layer address • Redirect - used to inform hosts of a better first hop for a destination. IIT Kanpur

31. 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 should accept 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. IIT Kanpur

32. Address Auto-configuration The problem • System bootstrap (“plug and play”) • Address renumbering Addressing Possibilities Manual Address configured by hand Autonomous Host creates address with no external interaction (e.g., link local) Semi-autonomous Host creates address by combining a priori information 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. IIT Kanpur

33. Auto-configuration in IPv6 • Link-local prefix concatenated with 64-bit MAC address. (Autonomous mode) • Prefix advertised by router concatenated with 64-bit MAC address. (Semi-autonomous mode.) • DHCPng (for server modes) • Can provide a permanent address (stateless mode) • Provide an address from a group of addresses, and keep track of this allocation (stateful mode) • Can provide additional network specific information. • Can register nodes in DNS. IIT Kanpur

34. 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 address continues to be valid for some time. IIT Kanpur

35. Upper Layer Issues • Minor changes in TCP • Maximum segment size should be based on Path MTU. • The packet size computation should take into account larger size of IP header(s). • Pseudo-header for checksum is different. • UDP checksum computation is now mandatory. • Most application protocol specifications are independent of TCP/IP - hence no change. • FTP protocol exchanges IPv4 addresses - hence needs to be changed. IIT Kanpur

36. 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.) IIT Kanpur

37. 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 redefined to do processing for both ‘A’ and ‘AAAA’ type records IIT Kanpur

38. Socket API • “Sockets” interface – the de facto standard API for TCP/IP Applications. • Need to change Socket API in order to reflect the increased address length in IPv6. • Also need to make new features like flow label, visible to applications. • A few new library routines • Complete source and binary compatibility with original API. • One can have some sockets using IPv4 and others using IPv6. IIT Kanpur

39. Transition to IPv6: Design Goal • No “flag”day. • 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 IIT Kanpur

40. 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. IIT Kanpur

41. 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 IPv4 address (like IPv4-compatible address). • Host to host, router to host IIT Kanpur

42. Transition mechanism: Translation • This will allow communication between IPv6 only hosts 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 IIT Kanpur

43. NAT-PT • Combination of Network Address Translation (NAT) and Protocol Translation (PT) • Meant for communication between IPv6-only and IPv4-only nodes. • No change is needed on the IPv6-only nodes. • But translation is not stateless. • Hence, single point of failure. IIT Kanpur

44. NAPT-PT • Network Address Port Translation + Protocol Translation • In addition to changing IP address, changes the port number also in the transport layer header. • It will allow IPv6 nodes to communicate with IPv4 nodes transparently using a single IPv4 address. IIT Kanpur

45. 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, not necessarily on all physical links. • Uses IPv4-translatable addresses. • Assumes that there is an IPv4 address pool of addresses for the subnet. IIT Kanpur

46. 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. IIT Kanpur

47. 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 path upgraded to V6. IIT Kanpur

48. Transition Options for User Sites • Incrementally upgrade V4 hosts to dual V4/V6 • Use IPv4-compatible addresses with existing IPv4 address 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 IPv6 addresses • Connect IPv6 router to an IPv6-enabled ISP. • Install translators like NAT-PT or SIIT. IIT Kanpur

49. Thank You IIT Kanpur