Chapter 4a, Network Layer (IP Addresses) Modified by John Copeland Georgia Tech for use in ECE3076 A note on the use of these ppt slides: We¶re making these slides freely available to all (faculty, students, readers). They¶re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we¶d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996-2006 J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top Down Approach Featuring the Internet, 5th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2009. Network Layer 4-1 Chapter 4: Network Layer Chapter goals: understand principles behind network layer services: network layer service models forwarding versus routing how a router works routing (path selection) dealing with scale advanced topics: IPv6, mobility instantiation, implementation in the Internet Network Layer 4-2 Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the datagram networks 4.3 What·s inside a router 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.7 Broadcast and multicast routing Network Layer 4-3 delivers segments to transport layer network layer protocols in every host. router Router examines header fields in all IP datagrams passing through it application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical Network Layer 4-4 .Network layer transport segment from sending to receiving host on sending side encapsulates segments into datagrams on receiving side. routing of getting through single interchange algorithms Network Layer 4-5 .Two Key Network-Layer Functions forwarding: move analogy: routing: process of packets from router·s input to appropriate router output routing: determine planning trip from source to dest forwarding: process route taken by packets from source to dest. Interplay between routing and forwarding routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 value in arriving packet¶s header 0111 1 3 2 Network Layer 4-6 . Network Layer 4-7 . two end hosts and intervening routers establish virtual connection routers get involved network vs transport layer connection service: network: between two hosts (may also involve intervening routers in case of VCs) transport: between two processes ATM.25 before datagrams flow. X.Connection setup 3rd important function in some network architectures: frame relay. g..Network service model Q: What service model for ´channelµ transporting datagrams from sender to receiver? Example services for individual datagrams: guaranteed delivery guaranteed delivery with less than 40 msec delay ´best effortµ (e. IP) Example services for a flow of datagrams: in-order datagram delivery guaranteed minimum bandwidth to flow restrictions on changes in interpacket spacing Network Layer 4-8 . Network layer service models: Network Architecture Internet ATM ATM ATM ATM Service Model Congestion Bandwidth Loss Order Timing feedback no yes yes no no no yes yes yes yes no yes yes no no no (inferred via loss) no congestion no congestion yes no Guarantees ? best effort none CBR VBR ABR UBR constant rate guaranteed rate guaranteed minimum none Network Layer 4-9 . 2 Virtual circuit and 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.3 What·s inside a router 4.Chapter 4: Network Layer 4.7 Broadcast and multicast routing Network Layer 4-10 .6 Routing in the datagram networks 4. 1 Introduction 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4. but: service: host-to-host no choice: network provides one or the other implementation: in network core Network Layer 4-11 .Network layer connection and connection-less service datagram network provides network-layer connectionless service VC network provides network-layer connection service analogous to the transport-layer services. teardown for each call before data can flow each packet carries VC identifier (not destination host address) every router on source-dest path maintains ´stateµ for each passing connection link. buffers) may be allocated to VC (dedicated resources = predictable service) Network Layer 4-12 .Virtual circuits ´source-to-dest path behaves much like telephone circuitµ performance-wise network actions along source-to-dest path call setup. router resources (bandwidth. 2. one number for each link along path entries in forwarding tables in routers along path packet belonging to VC carries VC number (rather than dest address) VC number can be changed on each link. New VC number comes from forwarding table Network Layer 4-13 .VC implementation a VC consists of: 1. 3. path from source to destination VC numbers. Forwarding table VC number 12 22 32 1 2 3 Forwarding table in northwest router: Incoming interface 1 2 3 1 « Incoming VC # 12 63 7 97 « interface number Outgoing interface 3 1 2 3 « Outgoing VC # 22 18 17 87 « Routers maintain connection state information! Network Layer 4-14 . 25 not used in today·s Internet application transport 5. X. Accept call 2. Initiate call physical 6. Data flow begins network 4. frame-relay. maintain teardown VC used in ATM.Virtual circuits: signaling protocols used to setup. incoming call transport network data link physical Network Layer 4-15 . Call connected data link 1. Receive data application 3. Receive data data link physical Network Layer 4-16 . Send data physical application transport network 2.Datagram networks (Internet) no call setup at network layer routers: no state about end-to-end connections no network-level concept of ´connectionµ packets forwarded using destination host address packets between same source-dest pair may take different paths (network congestion is busty) application transport network data link 1. telephones complexity at ´edgeµ complexity inside many link types network different characteristics uniform service difficult Network Layer 4-17 . datagram) data exchange among ATM (VC) evolved from telephony computers human conversation: ´elasticµ service. perform service control. no strict strict timing. reliability timing req. error recovery ´dumbµ end systems simple inside network. requirements ´smartµ end systems (computers) need for guaranteed can adapt.Datagram or VC network: why? Internet (IP. 4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.7 Broadcast and multicast routing Network Layer 4-18 .6 Routing in the datagram networks 4. 1 Introduction 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.Chapter 4: Network Layer 4.3 What·s inside a router 4.2 Virtual circuit and 4. BGP) forwarding datagrams from incoming to outgoing link Network Layer 4-19 .Router Architecture Overview Two key router functions: run routing algorithms/protocol (RIP. OSPF. .. lookup output port using forwarding table in input port memory goal: complete input port processing at ¶line speed· queuing: if datagrams arrive faster than forwarding rate into switch fabric Network Layer 4-20 .Input Port Functions Physical layer: bit-level reception Data link layer: e. Ethernet see chapter 5 Decentralized switching: given datagram dest.g. Three types of switching fabrics Network Layer 4-21 . Switching Via Memory First generation routers: traditional computers with switching under direct control of CPU packet copied to system·s memory speed limited by memory bandwidth (2 bus crossings per datagram) Input Port Memory Output Port System Bus Network Layer 4-22 . Cisco 1900: sufficient speed for access and enterprise routers (not regional or backbone) Network Layer 4-23 .Switching Via a Bus datagram from input port memory to output port memory via a shared bus bus contention: switching speed limited by bus bandwidth 1 Gbps bus. Switching Via An Interconnection Network overcome bus bandwidth limitations Banyan networks, other interconnection nets initially developed to connect processors in multiprocessor Advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. Cisco 12000: switches Gbps through the interconnection network Network Layer 4-24 Output Ports Buffering required when datagrams arrive from fabric faster than the transmission rate Scheduling discipline chooses among queued datagrams for transmission Network Layer 4-25 Output port queueing buffering when arrival rate via switch exceeds output line speed queueing (delay) and loss due to output port buffer overflow! Network Layer 4-26 Input Port Queuing Fabric slower than input ports combined -> queueing may occur at input queues Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward queueing delay and loss due to input buffer overflow! Network Layer 4-27 . Forwarding table Destination Address Range 2^32 = 4 billion possible entries Link Interface 11001000 00010111 00010000 00000000 through 11001000 00010111 00010111 11111111 (2^11 = 2048 addresses) 11001000 00010111 00011000 00000000 through 11001000 00010111 00011000 11111111 (2^8 = 256 addresses) 11001000 00010111 00011001 00000000 through 11001000 00010111 00011111 11111111 (2^11 = 2048 addresses) 0 1 2 otherwise 3 Network Layer 4-28 . Longest prefix matching Prefix Match 11001000 00010111 0001 0 11001000 00010111 0001 1000 11001000 00010111 0001 1 otherwise Examples Size /21 /24 /21 Link Interface 0 1 2 3 Which interface? Which interface? DA: 11001000 00010111 0001 0110 1010 0001 DA: 11001000 00010111 0001 1000 1010 1010 DA: 11001000 00010111 0001 1100 1010 1010 Why do we use prefixes of different lengths? Why do some IP addresses match more than one prefix? Network Layer 4-29 . 7 Broadcast and multicast routing Network Layer 4-30 .6 Routing in the datagram networks 4. 1 Introduction 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.3 What·s inside a router 4.2 Virtual circuit and 4.Chapter 4: Network Layer 4. UDP Routing protocols path selection RIP.The Internet Network layer Host. BGP IP protocol addressing conventions datagram format packet handling conventions Network layer forwarding table ICMP/IP protocol error reporting router ´signalingµ Link layer physical layer Network Layer 4-31 . OSPF. router network layer functions: Transport layer: TCP. Chapter 4: Network Layer 4.6 Routing in the datagram networks 4. 1 Introduction 4.2 Virtual circuit and 4.7 Broadcast and multicast routing Network Layer 4-32 .4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.3 What·s inside a router 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4. timestamp. total datagram length (bytes) for fragmentation/ reassembly how much overhead with TCP? 20 bytes of TCP* 20 bytes of IP = 40 bytes + app layer overhead data (variable length. specify list of routers to visit. usually 12-20 bytes Network Layer 4-33 . type of length ver service len fragment flgs 16-bit identifier offset time to upper header layer live checksum 32 bit source IP address 32 bit destination IP address Options (if any) E.IP datagram format IP protocol version number header length (bytes) ´typeµ of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to 32 bits head. record route taken.g. typically a TCP or UDP segment) *plus options. Divide "maximum data bytes" by 8: 1480/8 = 185 to get offset increment 4.. . 2.20 = 1480 (max. data bytes" = 20 +1480 = 1500 Length of last fragment = 20 + remaining data bytes = 20 + 3980 . Length of each fragment (except last) = 20 + "max. . Offset of each fragment "n" (n = 0. bytes of data in each fragment) 3.. 370. 185.) = n x "offset increment": 0. Subtract 20 from original length: 4000 -20 = 3980 (bytes of "IP data") 2. Subtract 20 from new MTU: 1500.. 1.2 x 1480 = 1040 Network Layer 4-34 .IP Fragmentation and Reassembly Example 4000 byte datagram MTU = 1500 bytes length =4000 ID =x fragflag =0 offset =0 One large datagram becomes several smaller datagrams length =1500 ID =x ID =x ID =x fragflag =1 fragflag =1 fragflag =0 offset =0 offset =185 offset =370 1480 bytes in data field offset = 1480/8 length =1500 length =1040 Steps: 1.. 5. largest possible link-level frame.IP Fragmentation & Reassembly network links have MTU (max. different MTUs large IP datagram divided (´fragmentedµ) within net one datagram becomes several datagrams ´reassembledµ only at final destination IP header bits used to identify. DNF (do not fragment) causes a ICMP response (and dropped datagram) instead of fragmentation.transfer size) . . The sender then resends future datagrams with smaller size (may fragment itself or Network Layer 4-35 reduce MSS for TCP). order related fragments fragmentation: in: one large datagram out: 3 smaller datagrams Blue: IP Header reassembly Another fragment flag. different link types. 6 Routing in the datagram networks 4. 1 Introduction 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.2 Virtual circuit and 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.7 Broadcast and multicast routing Network Layer 4-36 .3 What·s inside a router 4.Chapter 4: Network Layer 4. 1.IP Addressing: introduction IP address: 32-bit 223.2 223. 223.2.1 223.1.1 Could advertise a single route to Inet.1.1.1.1.4 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Network Layer 4-37 .1.2 223.3 223.3.1.3.3.2 223. and router interface interface: connection between host/router and physical link (sometimes called a "port").2. router·s typically have multiple interfaces host typically has one interface IP addresses associated with each interface 223.2.1.0/22 223.1.0.1.27 223.9 223.1.1 identifier for host.1.1.1. 1.1.1.1.1.3.3.1 223.3.4 223.1.Subnets IP address: subnet part (high order bits) host part (low order bits) What·s a subnet ? device interfaces with same subnet part of IP address can physically reach each other without intervening router 223.3 223.1 223.1.1.2 223.1.2 network consisting of 3 subnets Network Layer 4-38 .1.2.1.27 subnet 223.1.1 223.2.1.2 223.1.9 223.2. Subnets Recipe To determine the subnets. creating islands of isolated networks.0/24 Subnet mask: /24 Higher Order Subnet Network Layer 4-39 .1.1.0. Each isolated network is called a subnet. 223. detach each interface from its host or router.3.2.0/22 223.0/24 223.1.1.1.0/24 223. 0 223.1.2 223.1.1.0 223.2.1.3 223.9.1 223.1.1.1 223.1.3.7.8.6 223.1.1.4 223.1 223.3.2 223.2 Network Layer 4-40 .8.9.1.1.3.1.7.1.1 223.1 223.1.1.2 223.1.1.2.1.1 223.27 223.1.Subnets How many? 223.2.1. 000) addresses Class C = /24 = 2^8 (256) addresses Network Layer 4-41 . where x is # bits in subnet portion of address subnet part host part 11001000 00010111 00010000 00000000 200.16.000) addresses Class B = /16 = 2^16 (65.c.600.IP addressing: CIDR CIDR: Classless InterDomain Routing subnet portion of address of arbitrary length address format: a.d/x.0/23 Original scheme: Class A = /8 = 2^24 (16.b.23. IP addresses: how to get one? Q: How does host get IP address? hard-coded by system admin in a file control-panel->network->configuration>tcp/ip->properties UNIX: /etc/rc.config file. or use 'ifconfig' DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server ´plug-and-playµ (more in next chapter) Wintel: Network Layer 4-42 . org/ .20.Internet Assigned Numbers Authority Network Layer 4-43 .23. «.. Autonomous Systems (AS) buy connectivity from ISPs.0/23 200.23.0/20 200...0/23 «.18.IP addresses: how to get one? Q: How does network get subnet part of IP addr? A: gets allocated portion of its provider ISP·s address space (or space assigned to organization*).0/23 * see http://www.30.16. Organization 7 11001000 00010111 00010000 00000000 11001000 00010111 00010000 00000000 11001000 00010111 00010010 00000000 11001000 00010111 00010100 00000000 «.0/23 200.23.23. 11001000 00010111 00011110 00000000 200.23. Small companies may lease IP addresses from ISP as well. ISP's block Organization 0 Organization 1 Organization 2 . 200.iana.16. Hierarchical addressing: route aggregation Hierarchical addressing allows efficient advertisement of routing information: Organization 0 200. .18.23.16.0/20µ Internet 200.16.30. .0/23 Organization 2 200. . .0/23 Organization 1 200.23.23.0/23 ISPs-R-Us ´Send me anything with addresses beginning 199.20.0/16µ Network Layer 4-44 . .0.23.0/23 Organization 7 .23. Fly-By-Night-ISP ´Send me anything with addresses beginning 200.31. 0/23 Organization 7 .23.18.16. .30.23.0/23 ISPs-R-Us Organization 1 200. . Fly-By-Night-ISP Internet 200.Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 (who switched ISPs) ´Send me anything with addresses beginning 200. .0/23 1101000 00011001 0001 001x xxxxxxxx Network Layer 4-45 .0.23.0/23 200.0/16 or 200.0/23 ´Send me anything with addresses beginning 199. .23.16.0/20µ 1101000 00011001 0001 xxxx xxxxxxxx Organization 2 Organization 0 200.23.31. .18.20.23. 255.240. /20 represents a 32-bit binary number that has 20 bits at left and 12 zeros at the right: 11111111 11111111 11110000 00000000 This number in dotted decimal format is: 255. Network Layer 4-46 .0/20 as the ´subnet maskµ.Textbook refers to /20 in the network designator 200.16.0 A network designator is incomplete without the network mask.23. 1->0) Network Layer .The (sub)network mask can change: an IP address into the corresponding network address (for comparison in a router forwarding table). Match[i] = {(IP & mask[i] == Network_addr[i]} an IP address (or network address) into the network Broadcast Address: Broadcast_addr = IP | ~mask ´&µ bitwise AND ´|µ bitwise OR ´~µ bitwise inversion (0->1. IP Address Bitwise Calculations 200. x -> 0 11111111 11111111 11110000 00000000 Minimum Host Address: x -> 0 1101000 00011001 00010000 00000000 Maximum Host Address: x -> 1 1101000 00011001 00011111 11111111 Minimum host address is the ´Network Addressµ Maximum host address is the ´Broadcast Addr.16.µ Network Layer 4-48 . 0 or 1 -> 1.23.0/20 1101000 00011001 0001xxxx xxxxxxxx Network Mask. 16.0/20 1101000 00011001 0001xxxx xxxxxxxx Byte 3 is the ´Split Byte Byte 4 is ´Host Onlyµ.Sum to 256 --------------> Network Layer 4-49 .IP Address Dotted-Decimal Calculations 200. 1 & 2 are ´Network Onlyµ No. Network Bits i the "S lit B te Mask Val e of S lit B te Network art Host art is Multi le from Zero to: of: <--------.23. 255) Number of Host Addresses = 2^12 = (15+1)*256 Network Layer 4-50 .240.2 200.16.(16+15).0/20 1101000 00011001 0001xxxx xxxxxxxx Byte 3 is the ´Split Byte (4 network bits) Byte 4 is ´Host Onlyµ.23.255.IP Address Dotted-Decimal Calculations .31. Networ in the "Split its yte 4 Mas alue of Split yte (11110000) 240 Networ Part ost Part is Multiple from ero to: (00001111) of: 16 15 Network Mask = 255.23.23.16. 1 & 2 are ´Network Onlyµ No.) = 200.0 Min. (Network Addr.23. Host Addr.0 Maximum Host Address = 200.255 (Broadcast Address = 200. iana..com) assigns domain names. verisign.g. resolves disputes * Internet Assigned Numbers Authority ..icann. Q: How does an ISP (or organization) get a block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers (www.org) allocates addresses (no. IANA* does this) manages DNS (domain names can be registered through several dozen registries (e.org Network Layer 4-51 .IP addressing: the last word.www.. 29.0.0/24 10.0.2 All datagrams leaving local network have same single source NAT IP address: 138.0..4 138.0.0.3 10.7.76.0.0.0.76.0.0/24 address for source.0. destination (as usual) Network Layer 4-52 .29.g.NAT: Network Address Translation rest of Internet local network (e.1 10.7 10. home network) 10. different source port numbers Datagrams with source or destination in this network have 10. NAT: Network Address Translation Motivation: local network uses just one IP address as far as outside world is concerned: range of addresses not needed from ISP: just one IP address for all devices can change addresses of devices in local network without notifying outside world can change ISP without changing addresses of devices in local network devices inside local net not explicitly addressable. visible by outside world (a security plus). Network Layer 4-53 . remote clients/servers will respond using (NAT IP address. port #) stored in NAT table Network Layer 4-54 . new port #) . port #) to (NAT IP address. new port #) in dest fields of every incoming datagram with corresponding (source IP address. (in NAT translation table) every (source IP address. new port #) translation pair remember incoming datagrams: replace (NAT IP address. port #) of every outgoing datagram to (NAT IP address.NAT: Network Address Translation Implementation: NAT router must: outgoing datagrams: replace (source IP address. . . new port #) as destination addr. 80 10.0. Client port and Client port 10. 80.29.0.119.0.0. 80 source addr from 128.3 4: NAT router changes datagram dest addr from 138. 80 D: 10.0.119.7.119.0. 3345 to 138.1.2 4 3 3: Reply arrives dest. 3345 «« «« 10.186.0.186.76.4 138.119.0.119.29.76.1.0.7.29.40.186. 5001 S: 128.0.186.7.7. 5001 2 D: 128. 5001 to 10.0. 5001 from 128. 5001.29.1.76.0. port are not changed) 1 S: 138.0.0. 5001 10.76.40. 3345 NAT translation table WAN side: Server addr LAN side addr & port.7. 80 D: 138.1 (Server IP.0.76.76.0.1. S: 10. 3345 Network Layer 4-55 .NAT: Network Address Translation 1: host 10.7 S: 128.29. 80 Slide modified 10/19/2008 by JAC 10.0.0.40.40.186.119. address: 138.0.1.186.29.0.1 2: NAT router sends datagram to changes datagram 128.40.186.40. 80 10.40.119. 3345 updates table D: 128. 000 simultaneous connections with a single LAN-side address! [Actually more if the translation table has outside IP.port as a factor. NAT is controversial [?]: routers should only process up to layer 3 violates end-to-end argument NAT possibility must be taken into account by app designers. since duplication is not likely]. eg.NAT: Network Address Translation 16-bit port-number field: 60. Many such implementations do not change the port number. P2P applications address shortage should instead be solved by IPv6 Network Layer 4-56 . 5 Routing algorithms Link state Distance Vector Hierarchical routing 4.7 Broadcast and multicast routing Network Layer 4-57 .2 Virtual circuit and 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.6 Routing in the datagram networks 4.3 What·s inside a router 4. 1 Introduction 4.Chapter 4: Network Layer 4. 4. network unreachable error reporting: unreachable 3 1 dest host unreachable host.ICMP: Internet Control Message Protocol used by hosts & routers to Type Code description communicate network-level 0 0 echo reply (ping) information 3 0 dest. or 10 0 router discovery 12: code plus IP header and 11 0 TTL expired following 8 bytes of IP 12 0 bad IP header datagram causing error (would include UDP or TCP port numbers) Slide modified 10/19/2008 by JAC Network Layer 4-58 . 11. network. 3 2 dest protocol unreachable protocol 3 3 dest port unreachable echo request/reply (used by 3 6 dest network unknown ping) 3 7 dest host unknown network-layer ´aboveµ IP: 4 0 source quench (congestion control .not used) ICMP messages carried in 8 0 echo request (ping) IP datagrams 9 0 route advertisement ICMP message: type=3. port. Unlikely port number When nth datagram arrives to nth router: Router discards datagram And sends to source an ICMP message (type 11. Traceroute does DNS lookup to find name of router (if any) arrives. code 3) When source gets this ICMP. Network Layer 4-59 * or ICMP pings Slide modified 10/19/2008 by JAC . code 0) Datagram includes router IP address.Traceroute and ICMP Source sends series of UDP segments* to dest host When ICMP message First has TTL =1 Second has TTL=2. stops. etc. source calculates RTT Traceroute does this 3 times Stopping criterion UDP segment eventually arrives at destination host Destination returns ICMP ´host unreachableµ packet (type 3. 3 What·s inside a router 4.4 IP: Internet Protocol Internet Datagram format IPv4 addressing ICMP IPv6 RIP OSPF BGP 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.Chapter 4: Network Layer 4.2 Virtual circuit and 4.7 Broadcast and multicast routing Network Layer 4-60 . 1 Introduction 4.6 Routing in the datagram networks 4. B = /16 (65k). Additional motivation: header format helps speed processing/forwarding header changes to facilitate QoS IPv6 datagram format: fixed-length 40 byte header no fragmentation allowed *Before CIDR (Classless Internet Domain Routing). C = /24 (255 addresses) If an org needed 260 addresses. Network Layer 4-61 . NAT and CIDR* have fixed the problem for now). a Class B (65. there were only three subnet sizes (classes): Class A= /8 (4M).535) was allocated.IPv6 Initial motivation: 32-bit address space soon to be completely allocated (however. c.d/96 ´:0:µ=´:0000:µ 2 byte hex: IPv4 address can become an IPv6 sub-net with 32 bits for ´hostµ addresses (4e9 hosts) Slide modified 10/19/2008 by JAC Network Layer 4-62 . Next header: identify upper layer protocol for data ´6to4 Tunnelingµ 4-byte IPv4 -> 16-byte IPv6 a.d -> :0:0:0:0:a.b:c.µ (concept of´flowµ not well defined).IPv6 Header (Cont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same ´flow.b. indicated by ´Next Headerµ field (segmentation is done in Options Header) ICMPv6: new version of ICMP additional message types. ´Packet Too Bigµ multicast group management functions Network Layer 4-63 .g. but outside of header.Other Changes from IPv4 Checksum: removed entirely to reduce processing time at each hop Options: allowed. e. Transition From IPv4 To IPv6 Not all routers can be upgraded simultaneous no ´flag daysµ How will the network operate with mixed IPv4 and IPv6 routers? Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers Network Layer 4-64 . Tunneling Logical view: A IPv6 B IPv6 tunnel E IPv6 F IPv6 Physical view: A IPv6 B IPv6 IPv4 IPv4 E IPv6 F IPv6 Network Layer 4-65 . Tunneling Logical view: A IPv6 B IPv6 tunnel E IPv6 F IPv6 Physical view: A IPv6 Flow: X Src: A Dest: F B IPv6 C IPv4 D IPv4 E IPv6 F IPv6 Flow: X Src: A Dest: F Src:B Dest: E Flow: X Src: A Dest: F Src:B Dest: E Flow: X Src: A Dest: F data data data data A-to-B: IPv6 B-to-C: IPv6 inside IPv4 B-to-C: IPv6 inside IPv4 E-to-F: IPv6 Network Layer 4-66 .