Advanced Computer Networks: Lecture 26. This lecture will cover the following: basics of internetworking (heterogeneity); IPv6 wish list/planned support; IPv6 addresses; IPv4 packet format review; IPv6 packet format; IPv6 extension headers; IPv6 design controversies;...
CS716 Advanced Computer Networks By Dr. Amir Qayyum 1 Lecture No. 26 Internetworking • Basics of internetworking (heterogeneity) – IP protocol, address resolution, control messages, … • Routing • Global internets (scale) – Virtual geography and addresses – Hierarchical routing • Future internetworking: IPv6 • Multicast traffic • MPLS IPv6 History • Nextgeneration IP, previously denoted IPng • Intended to extend address space/routing limitations – Requires header change: new protocol for all nodes! – Try to include everything new with one change • IETF (Internet Engineering Task Force) solicited white papers • Many suggestions, merged in time to several options • IETF selected Simple Internet Protocol Plus (SIPP with some modifications, dubbed it version 6 IPv6 and NAT • Address space pressure reduced with NAT technique – Few public addresses with Network Address Translation – Driving force reduces and so the rapid transition! – Will IPv6 succeed in completely replacing IPv4 ? ? ? Local network Local network with many hosts with many hosts NAT Box Internet Internet IPv6 Wish List / Planned Support • • • • • • • • • 128bit addresses Multicast traffic Mobility Realtime traffic/quality of service guarantees Authentication and security Autoconfiguration: determining local IP address Endtoend fragmentation Protocol extensions (flexible protocol) Smooth transition spread over time is critical – Islands of v6 and then v4, traffic is tunneled in Internet IPv6 Addresses • Classless addressing/routing (similar to CIDR) • Address notation – String of eight 16bit hex values separated by colons e.g. 5CFA:0002:0000:0000:CF07:1234:5678:FFCD – Only one set of contiguous zeroes can be elided, e.g. 5CFA:0002::CF07:1234:5678:FFCD • Address assignment – Providerbased – Geographic 010 region ID provider ID subscriber ID subnet host IPv6 Address Prefix • 0000 0000 • 0000 001 • • • • • • • 0000 010 010 100 1111 1110 10 1111 1110 11 1111 1111 Other reserved (includes transition addresses) ISO NSAP (Network Service Access Point) allocation Novell IPX allocation providerbased unicast geographic unicast link local addresses site local addresses multicast addresses unassigned IPv4 Packet Format Review Version HLen 16 TOS 31 Length Ident TTL 19 Flags Protocol Offset Checksum SourceAddr DestinationAddr Options (variable) Pad (variable) Data • 20byte minimum • Mandatory fields not always used (e.g. fragmentation) • Options are unordered list of (name, value) pairs IPv6 Packet Format version priority payload length 16 31 24 flow label next header hop limit source address word 1 source address word 2 source address word 3 source address word 4 destination address word 1 destination address word 2 destination address word 3 destination address word 4 10 IPv6 Packet Format version priority payload length 16 31 24 flow label next header hop limit source address (4 words) destination address (4 words) option (variable number, usually fixed length) • 40byte minimum • Mandatory fields (probably) always used • Strict order on options reduces processing time (no need to parse irrelevant options) 11 IPv6 Packet Format • Priority and flow label – Support service guarantees – Allow “fair” bandwidth allocation • Payload length (header not included, unlike IPv4) • Next header – Combines options and protocol – Linked list of options – Ends with higherlevel protocol header (e.g. TCP) • Hop limit is TTL field renamed to match usage 12 IPv6 Extension Headers • Extension headers (options) appear in order Hopbyhop options misc. info. for routers Routing full/partial route to follow Fragmentation IP fragmentation info Authentication sender identification Encrypt security payload info. about contents Destination options info. for destination 13 IPv6 Extension Headers • Hopbyhop extension – Length is in bytes beyond mandatory 8 16 24 next header length type value 31 • Jumbogram option (packet longer than 65,535 bytes) – Payload length in main header set to 0 16 24 next header 194 payload length in bytes 31 14 IPv6 Extension Headers • Routing extension next header 31 16 24 no.of.address next address es strict/loose routing bitmap 1 – 24 addresses – Up to 24 “anycast” addresses target AS’s or providers – Next address tracks current target – Strict routing requires direct link, loose routing allows intermediate nodes 15 IPv6 Extension Headers • Fragmentation extension next header 16 reserved offset identification 31 29 resv M • Similar to IPv4 fragmentation – 13bit offset, – Lastfragment mark (M) • Larger fragment identification field 16 IPv6 Extension Headers • Security without bothering the routers • Authentication extension – Designed to be very flexible – Includes Security Parameters Index (SPI) and Authentication data at the end • Encryption extension – Called Encapsulation Security Payload (ESP) – Includes an SPI – All headers and data after ESP are encrypted 17 IPv6 Design Controversies Address length • 8byte – Less header overhead. Might run out in a few decades • 16byte – More overhead. Good for foreseeable future • 20byte – Even more overhead. Compatible with OSI • Variablelength – Difficult for router design 18 IPv6 Design Controversies Hop limit • 65,535 – 32hop paths are common now – In a decade, much longer paths possible • 255 – Limits lost packet lifetime (65,535 is far too long) – Good network design makes long paths unlikely • Source to backbone • Across backbone • Backbone to destination 19 IPv6 Design Controversies Maximum packet size • > 64kB: supercomputer/high bandwidth applications – Too much overhead to fragment data – Want much larger packets • 64 kB: longer packets incompatible with lowbandwidth lines – Consider 1MB packet across 1.5 Mbps line – Ties up line for greater than 5 seconds – Inconveniences interactive users 20 IPv6 Design Controversies Keep IP checksum ? • Yes – Removing checksum from IP analogous to removing brakes from a car • Lighter, so you go faster • Unprepared for the unexpected • No – Typically duplicated in data link and transport layers – Major expense in IPv4 routers – In case of IPv6, it is mandatory in UDP and TCP 21 IPv6 Design Controversies Mobile hosts • Direct or Indirect ? – Reconnect directly using canonical address – Use home and foreign agents to forward traffic • Mobility introduces asymmetry – Base station signal is strong, heard by mobile units – Mobile unit signal is weak and susceptible to interference, not heard by base station • No clearly superior design proposal 22 IPv6 Design Controversies Security • Where ? – Network layer: a standard service – Application layer • No viable standard • Applications susceptible to errors in network implementations • Too clunky to turn off • How ? – Political export/import issues – Cryptographic strength issues 23 .. .Lecture? ?No.? ?26 Internetworking • Basics of internetworking (heterogeneity) – IP protocol, address resolution, control messages, ... Across backbone • Backbone to destination 19 IPv6 Design Controversies Maximum packet size • > 64kB: supercomputer/high bandwidth applications – Too much overhead to fragment data – Want much larger packets