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05 network

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  • 1. Network layer Network Layer 4-1
  • 2. Network layerr transport segment from application sending to receiving host transport network data linkr on sending side puts physical segments into datagrams network data link network data link networkr on rcving side, delivers data link physical physical segments to transport layer physical network data link network data linkr network layer protocols in physical physical every host, router network network data link data link physical physical network data link physical application network transport data link network network physical data link network data link physical data link physical physical Network Layer 4-2
  • 3. Network layer functionsr Connection setup r Quality-of-service m datagram m provide predictable m connection-oriented, host- performance to-host connection r Fragmentationr Delivery semantics: m break-up packets based on m Unicast, broadcast, data-link layer properties multicast, anycast r Routing m In-order, any-order m path selection and packetr Security forwarding m secrecy, integrity, r Addressing authenticity m flat vs. hierarchicalr Demux to upper layer m global vs. local m next protocol m variable vs. fixed length m Can be either transport or network (tunneling) Network Layer 4-3
  • 4. The Internet Network layer Host, router network layer functions: Transport layer: TCP, UDP Routing protocols IP protocol •path selection •addressing conventions •RIP, OSPF, BGP •datagram formatNetwork •packet handling conventions layer forwarding ICMP protocol table •error reporting •router “signaling” Link layer physical layer Network Layer 4-4
  • 5. IP datagram format IP protocol version 32 bits number total datagram header length length (bytes) ver head. type of length (bytes) len service for “type” of data fragment 16-bit identifier flgs fragmentation/ offset max number time to upper reassembly Internet remaining hops live layer checksum (decremented at 32 bit source IP address each router) 32 bit destination IP address upper layer protocol to deliver payload to Options (if any) E.g. timestamp, record routehow much overhead data taken, specify with TCP? (variable length, list of routersr 20 bytes of TCP typically a TCP to visit. or UDP segment)r 20 bytes of IPr = 40 bytes + app layer overhead Network Layer 4-5
  • 6. Recall network layer functionsr How does IPv4 support.. m Connection setup m Delivery semantics m Security m Demux to upper layer m Quality-of-service m Fragmentation m Addressing m Routing Network Layer 4-6
  • 7. IP connection setupr Hourglass designr No support for network layer connections m Unreliable datagram service m Out-of-order delivery possible m Connection semantics only at higher layer m Compare to ATM and phone network… Network Layer 4-7
  • 8. Connectionless network layers r Postal service abstraction (Internet) m Model • no call setup or teardown at network layer • no service guarantees m Network support • no state within network on end-to-end connections • packets forwarded based on destination host ID • packets between same source-dest pair may take different paths application application transport transport network network data link 1. Send data 2. Receive data data link physical physical Network Layer 4-8
  • 9. Connection-oriented network layersr Circuit abstraction m Examples: ATM, frame relay, X.25, phone network m Model • call setup and signaling for each call before data can flow • guaranteed performance during call • call teardown and signaling to remove call m Network support • every router on source-dest path maintains “state” for each passing circuit • link, router resources (bandwidth, buffers) allocated to VC to guarantee circuit-like performanceapplication 5. Data flow begins 6. Receive data applicationtransport 4. Call connected transport 3. Accept call network 1. Initiate call network data link 2. incoming call data link physical physical Network Layer 4-9
  • 10. IP delivery semanticsr No reliability guarantees m Lossr No ordering guarantees m Out-of-order delivery possibler Unicast mostly m IP broadcast (255.255.255.255) not forwarded m IP multicast supported, but not widely used • 224.0.0.0 to 239.255.255.255 Network Layer 4-10
  • 11. IP securityr Weak support for integrity m IP checksum • IP has a header checksum, leaves data integrity to TCP/UDP • http://www.rfc-editor.org/rfc/rfc1141.txt m No support for secrecy, authenticityr IPsec m Retrofit IP network layer with encryption and authentication m http://www.rfc-editor.org/rfc/rfc2411.txt Network Layer 4-11
  • 12. IP demux to upper layerr http://www.rfc-editor.org/rfc/rfc1700.txt m Protocol type field • 1 = ICMP • 4 = IP in IP • 6 = TCP • 8 = EGP • 9 = IGP • 17 = UDP Network Layer 4-12
  • 13. IP quality of servicer IP originally had “type-of-service” (TOS) field to eventually support quality m Not used, ignored by most routersr Need to provide applications with performance guarantees m Mid 90s: Add circuits to the Internet! • Integrated services (intserv) and RSVP signalling • Per-flow end-to-end QoS support • Per-flow signaling and network resource allocation Network Layer 4-13
  • 14. Network service modelExample services for Example services for a individual datagrams: flow of datagrams:r guaranteed delivery r in-order datagramr guaranteed delivery delivery with less than 40 msec r guaranteed minimum delay bandwidth to flow r restrictions on changes in inter- packet spacing (jitter) Network Layer 4-14
  • 15. IP quality of servicer Protocols developed and standardized m RSVP signalling protocol m Intserv service modelsr Failed miserably…Why? m Complexity • Scheduling • Routing (pinning routes) • Per-flow signalling overhead m Lack of scalability • Per-flow state m Economics • Providers with no incentive to deploy • SLA, end-to-end billing issues m QoS a weak-link property • Requires every device on an end-to-end basis to support flow Network Layer 4-15
  • 16. IP quality of servicer Now it’s diffserv… m Use the “type-of-service” bits as a priority marking m http://www.rfc-editor.org/rfc/rfc2474.txt m http://www.rfc-editor.org/rfc/rfc2475.txt m http://www.rfc-editor.org/rfc/rfc2597.txt m http://www.rfc-editor.org/rfc/rfc2598.txt Network Layer 4-16
  • 17. IP Addressingr IP address: 223.1.1.1 m 32-bit identifier for host/router 223.1.1.2 223.1.2.1 interface 223.1.1.4 223.1.2.9 m routers typically have 223.1.2.2 multiple interfaces 223.1.1.3 223.1.3.27 m Addresses hierarchical (like post office) 223.1.3.1 223.1.3.2 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Network Layer 4-17
  • 18. IP Addressingr IP address: m network part (high order 223.1.1.1 bits) 223.1.2.1 m host part (low order bits) 223.1.1.2 223.1.1.4 223.1.2.9r What’s a network ? m all interfaces that can 223.1.1.3 223.1.3.27 223.1.2.2 physically reach each other without intervening LAN router m each interface shares 223.1.3.1 223.1.3.2 the same network part of IP address network consisting of 3 IP networks (for IP addresses starting with 223, first 24 bits are network address) Network Layer 4-18
  • 19. How did networks get IP addresses?r Total IP address size: 4 billionr Initially one large class (8-bit network, 24-bit host) m ISP given an 8-bit network number to manage m Each router keeps track of each network (28=256 routes) m Each network has 16 million hosts m Problem: one size does not fit allr Classful addressing m Accommodate smaller networks (LANs) m Class A: 128 networks, 16M hosts m Class B: 16K networks, 64K hosts m Class C: 2M networks, 256 hosts m Total routes potentially > 2,113,664 networks and network routes ! Network Layer 4-19
  • 20. IP address classes 8 16 24 32 Class A 0 Network ID Host ID 1.0.0.0 to 127.255.255.255 Class B 10 Network ID Host ID 128.0.0.0 to 191.255.255.255 Class C 110 Network ID Host ID 192.0.0.0 to 223.255.255.255 Class D 1110 Multicast Addresses 224.0.0.0 to 239.255.255.255 Class E 1111 Reserved for experiments Network Layer 4-20
  • 21. Special IP Addressesr Private addresses – http://www.rfc-editor.org/rfc/rfc1918.txt – Class A: 10.0.0.0 - 10.255.255.255 (10.0.0.0/8 prefix) – Class B: 172.16.0.0 - 172.31.255.255 (172.16.0.0/12 prefix) – Class C: 192.168.0.0 - 192.168.255.255 (192.168.0.0/16 prefix)r 127.0.0.1: local host (a.k.a. the loopback address) Network Layer 4-21
  • 22. IP Addressing problemsr Inefficient use of address space m Class A (rarely given out, sparse usage) m Class B = 64k hosts (sparse usage) • Very few LANs have close to 64K hostsr Address space depletion m Classes A and B take huge chunks of space but not used much m Not many class C addresses left to give outr Explosion of routes m Increasing use of class C explodes # of routes Network Layer 4-22
  • 23. IP addressing: CIDR r Original classful addressing m Use class structure (A, B, C) to determine network ID for route lookup r CIDR: Classless InterDomain Routing m Arbitrarily aggregate and split up adjacent network addresses variable network host part part 11001000 00010111 00010000 00000000 200.23.16.0/23 Network Layer 4-23
  • 24. CIDRr Assign any range of addresses to network m Allows one to split large network blocks into multiple smaller ones (increase usage of Class A & B) m Allows one to combine small network blocks into a single large one (reduce routes from Class C usage) Network Layer 4-24
  • 25. Getting IP addressesQ: How does network get IP addresses?A: organization gets allocated portion of its provider ISP’s address space m ISPs get it from ICANN: Internet Corporation for Assigned Names and Numbers • Allocates addresses, manages DNS, resolves disputes m Customers get sub-blocks from ISPsISPs block 11001000 00010111 00010000 00000000 200.23.16.0/20Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. ….Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 Network Layer 4-25
  • 26. IPv6r IPv4 running out of addressesr Need to replace it with a new network protocolr What changes should be made in…. • IP addressing • IP delivery semantics • IP quality of service • IP security • IP routing • IP fragmentation • IP error detection Network Layer 4-26
  • 27. IPv6r Initial motivation: 32-bit address space soon to be completely allocatedr Additional motivation: m Remove ancillary functionality • Speed processing/forwarding m Add missing, but essential functionality • header changes to facilitate QoS • new “anycast” address: route to “best” of several replicated servers Network Layer 4-27
  • 28. IPv6 Header (Cont)Priority: identify priority among datagrams in flowFlow Label: identify datagrams in same “flow.” (concept of“flow” not well defined).Next header: identify next protocol for data Network Layer 4-28
  • 29. IPv6 Changesr Scale – addresses are 128bit m Header size?r Simplification m Removes infrequently used parts of header m Removes checksum m 40 byte fixed header vs. 20+ byte variable header m Eliminates fragmentation Network Layer 4-29
  • 30. Transition From IPv4 To IPv6r Not all routers can be upgraded simultaneous m no “flag days” m How will the network operate with mixed IPv4 and IPv6 routers? m Tunneling: IPv6 carried as payload in an IPv4 datagram among IPv4 routers Network Layer 4-30
  • 31. Tunneling A B E F Logical view: tunnel IPv6 IPv6 IPv6 IPv6 A B E FPhysical view: IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Network Layer 4-31
  • 32. Tunneling A B E F Logical view: tunnel IPv6 IPv6 IPv6 IPv6 A B C D E FPhysical view: IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Flow: X Src:B Src:B Flow: X Src: A Dest: E Dest: E Src: A Dest: F Dest: F Flow: X Flow: X Src: A Src: A data Dest: F Dest: F data data data A-to-B: E-to-F: B-to-C: B-to-C: IPv6 IPv6 IPv6 inside IPv6 inside IPv4 IPv4 Network Layer 4-32
  • 33. Routing Network Layer 4-33
  • 34. Two Key Network-Layer Functionsr forwarding: move packets from router’s input to appropriate router outputr routing: determine route taken by packets from source to dest. m routing algorithms Network Layer 4-34
  • 35. Internet routing with IP addressesr Hop-by-hop forwarding based on destination IP carried by packet m Each packet has destination IP address m Each router has forwarding table of.. • destination IP à next hop IP address m IP route table calculated in network routersr Most prevalent way to route on the Internet m Distributed routing algorithm for calculating forwarding tables Network Layer 4-35
  • 36. Routing protocols Goal: determine “good” path (sequence of routers) thru network from source to dest.Graph abstraction for 5 routing algorithms: 3 B Cr Routing algorithms find 2 5 minimum cost paths A 2 1 F 3 through graph 1 2 D E 1 Network Layer 4-36
  • 37. Routing Algorithm classificationGlobal or decentralized information?Global: m all routers have complete topology, link cost info m “link state” algorithmsDecentralized: m router knows physically-connected neighbors, link costs to neighbors m iterative process of computation, exchange of info with neighbors m “distance vector” algorithms Network Layer 4-37
  • 38. Hierarchical Routingscale: with 200 million administrative autonomy destinations: r internet = network ofr can’t store all dest’s in networks routing tables! r each network admin mayr routing table exchange want to control routing in its would swamp links! own networkr Flat routing does not scale Network Layer 4-38
  • 39. Routing Hierarchiesr Key observation m Need less information with increasing distance to destination m Hierarchical routing • saves table size • reduces update traffic • allows routing to scale Network Layer 4-39
  • 40. Areasr Divide network into areas m Within area, each node has routes to every other node m Outside area • Each node has routes for other top-level areas only (not nodes within those areas) • Inter-area packets are routed to nearest appropriate border router Network Layer 4-40
  • 41. Internet Routing Hierarchyr Internet areas called Border routers “autonomous systems” m Special routers in AS (AS) that directly link to m administrative another AS autonomy • also run inter-AS routing protocol orr routers in same AS run border gateway same routing protocol protocol (BGP) with other gateway routers m “intra-AS” routing in other AS’s protocol (IGP) Network Layer 4-41
  • 42. Internet Routing Hierarchy C.b B.a A.a b A.c c a C a b a B d c A b Network Layer 4-42
  • 43. Inter-AS routingr Done using BGP (Border Gateway Protocol) m Uses distance-vector style algorithmsr BGP messages exchanged using TCP. m Advantages: • Simplifies BGP • No need for periodic refresh - routes are valid until withdrawn, or the connection is lost • Incremental updates m Disadvantages • BGP TCP spoofing attack • Congestion control on a routing protocol? • Poor interaction during high load (Code Red) • No authentication of route advertisements – Pakistan Youtube incident Network Layer 4-43
  • 44. ICMP: Internet Control Message Protocolr Essentially a network-layer protocol for passing control Type Code description messages 0 0 echo reply (ping)r used by hosts & routers to 3 0 dest. network unreachable communicate network-level 3 1 dest host unreachable information 3 2 dest protocol unreachable m error reporting: unreachable host, network, port, protocol 3 3 dest port unreachable m echo request/reply (used by 3 6 dest network unknown ping) 3 7 dest host unknownr network-layer “above” IP: 4 0 source quench (congestion m ICMP msgs carried in IP control - not used) datagrams 8 0 echo request (ping)r ICMP message: type, code plus 9 0 route advertisement first 8 bytes of IP datagram causing error 10 0 router discoveryr http://www.rfc- 11 0 TTL expired editor.org/rfc/rfc792.txt 12 0 bad IP header Network Layer 4-44
  • 45. ICMP and tracerouter What do “real” Internet delay & loss look like?r Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: m sends three packets that will reach router i on path towards destination m router i will return packets to sender m sender times interval between transmission and reply. 3 probes 3 probes 3 probes Network Layer 4-45
  • 46. ICMP and tracerouter Source sends series of r When ICMP message UDP segments to dest arrives, source calculates m First has TTL =1 RTT m Second has TTL=2, etc. r Traceroute does this 3 m Unlikely port number timesr When nth datagram arrives Stopping criterion to nth router: r UDP segment eventually m Router discards datagram arrives at destination host m And sends to source an r Destination returns ICMP ICMP message (type 11, “host unreachable” packet code 0) (type 3, code 3) m Message includes name of r When source gets this router& IP address ICMP, stops. Network Layer 4-46
  • 47. Examplestraceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms link10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * * * means no response (probe lost, router not replying)19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms Network Layer 4-47
  • 48. Try itr Some routers labeled with airport code of city they are located in m traceroute www.yahoo.com • Packets go to SEA, back to PDX, SJC m traceroute www.oregonlive.com • Packets go to SMF, SFO, SJC, NYC, EWR. m traceroute www.uoregon.edu • Packets go to Pittock block to Eugene m traceroute www.lclark.edu • Packets go to SEA and back to PDX Network Layer 4-48
  • 49. Internet overview completer Technical background for the rest of the course Network Layer 4-49

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