11 CS716 Advanced Computer Networks By Dr. Amir Qayyum

2 Lecture No. 26

3 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

4 IPv6 - History Next-generation 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

5 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 ? ? ? Internet NAT Box Local network with many hosts

6 IPv6 Wish List / Planned Support 128-bit addresses Multicast traffic Mobility Real-time traffic/quality of service guarantees Authentication and security Autoconfiguration: determining local IP address End-to-end fragmentation Protocol extensions (flexible protocol) Smooth transition spread over time is critical –Islands of v6 and then v4, traffic is tunneled in Internet

7 IPv6 Addresses Classless addressing/routing (similar to CIDR) Address notation –String of eight 16-bit 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 –Provider-based –Geographic subscriber ID provider ID region IDsubnet host 010

8 IPv6 Address - Prefix reserved (includes transition addresses) ISO NSAP (Network Service Access Point) allocation Novell IPX allocation 010provider-based unicast 100geographic unicast link local addresses site local addresses multicast addresses Otherunassigned

9 IPv4 Packet Format Review 20-byte minimum Mandatory fields not always used (e.g. fragmentation) Options are unordered list of (name, value) pairs VersionHLen TOSLength IdentFlagsOffset TTLProtocolChecksum SourceAddr DestinationAddr Options (variable) Pad (variable) Data

10 IPv6 Packet Format destination address word 4 destination address word 3 destination address word 2 destination address word 1 source address word 4 source address word 3 source address word 2 source address word 1 payload lengthnext headerhop limit versionpriorityflow label

11 IPv6 Packet Format 40-byte minimum Mandatory fields (probably) always used Strict order on options reduces processing time (no need to parse irrelevant options) option (variable number, usually fixed length) destination address (4 words) source address (4 words) payload lengthnext headerhop limit versionpriorityflow label

12 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 higher-level protocol header (e.g. TCP) Hop limit is TTL field renamed to match usage

13 IPv6 Extension Headers Extension headers (options) appear in order 1.Hop-by-hop options....misc. info. for routers 2.Routing full/partial route to follow 3.Fragmentation IP fragmentation info 4.Authentication sender identification 5.Encrypt security payload info. about contents 6.Destination options.... info. for destination

14 IPv6 Extension Headers Hop-by-hop extension –Length is in bytes beyond mandatory 8 Jumbogram option (packet longer than 65,535 bytes) –Payload length in main header set to 0 next headerlengthtype value payload length in bytes next header01940

15 IPv6 Extension Headers Routing extension –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 next header0no.of.address es next address strict/loose routing bitmap 1 – 24 addresses

16 IPv6 Extension Headers Fragmentation extension Similar to IPv4 fragmentation –13-bit offset, –Last-fragment mark (M) Larger fragment identification field next headerreservedoffsetMresv identification

17 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

18 IPv6 Design Controversies Address length 8-byte –Less header overhead. Might run out in a few decades 16-byte –More overhead. Good for foreseeable future 20-byte –Even more overhead. Compatible with OSI Variable-length –Difficult for router design

19 IPv6 Design Controversies Hop limit 65,535 –32-hop 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

20 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 low-bandwidth lines –Consider 1MB packet across 1.5 Mbps line –Ties up line for greater than 5 seconds –Inconveniences interactive users

21 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

22 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

23 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