1. TCP/IP Architecture Advanced Features1 Chapter 3 TCP/IP Architecture Advanced Features Some of these slides are copyrighted by: Computer Networking: A Top Down Approach 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. Departamento de Tecnología Electrónica

2. 2 Chapter 3: Network Layer. Associated Protocols r Chapter goals: m understanding advanced principles behind network layer services: address translation routing (path selection) network layer error control IPv4 address dynamic configuration Advanced topics: IPv6. m understanding congestion control in TCP TCP/IP Architecture Advanced Features

3. 3 Chapter 2 outline r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6 TCP/IP Architecture Advanced Features

4. 4 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

5. 5 ICMP: Internet Control Message Protocol r used by hosts & routers to communicate network-level information m error reporting: unreachable host, network, port, protocol m warnings from routers or receivers r network-layer above IP: m ICMP msgs carried in IP datagrams (but ICMP is not a transport-layer protocol!) r all the nodes using IP must have ICMP implemented r ICMP msgs are only created for the first IP fragment TCP/IP Architecture Advanced Features

6. 6 ICMP: Internet Control Message Protocol r Message format m ICMP msgs carried in IP datagrams Protocol field = 1 in IP header Source IP addr = host sending ICMP msg Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 5 0 ICMP redirect 8 0 echo request (ping) 11 0 TTL expired TCP/IP Architecture Advanced Features

7. 7 ICMP: Internet Control Message Protocol r Ping m Sends data pkt and waits for a response m Based on Type 8 and Type 0 ICMP messages m Functions: Check host connectivity Ping sends pkts with unique seq numbers –Detection ofduplicate, reordered and eliminated pkts Ping use cheksums in every pkt –Detection of corrupted pkts Ping allows RTT (Round Trip Time) calculation Ping allows the detection of other ICMP messages. TCP/IP Architecture Advanced Features

8. 8 ICMP: Internet Control Message Protocol r Ping Echo request and echo reply 1 byte 1 byte 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Id | Sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 8 (Echo request) or 0 (Echo reply) Code: 0 Id: number of identificación (optional) Sequence number (optional) TCP/IP Architecture Advanced Features

9. 9 ICMP: Internet Control Message Protocol r Ping Syntax ping [options] destination_host Options -w timeout Timeout in milliseconds to wait for each reply. -i TTL Time To Live. -v TOS Type Of Service. -a Resolve addresses to hostnames. -n count Number of echo requests to send. -t Ping the destination host until interrupted. To see statistics and continue type Control-Break; To stop type Control-C. -l size Send buffer size. -f Set Don't Fragment flag in packet (IPv4-only). -r count Record route for count hops (IPv4-only). -s count Timestamp for count hops (IPv4-only). -j host_list Loose source route along host_list (IPv4-only). -k host_list Strict source route along host_list (IPv4-only). destination_host The name of the remote host -R Use routing header to test reverse route also (IPv6-only). -S srcaddr Source address to use (IPv6-only). -4 Force using IPv4. -6 Force using IPv6 TCP/IP Architecture Advanced Features

10. 10 ICMP: Internet Control Message Protocol r Tracert (Trace route) m Source sends echo requests to dest First has TTL =1 Second has TTL=2, etc. m When nth datagram arrives to nth router: Router discards datagram And sends to source an ICMP message (type 11, code 0) Message includes name of router& IP address m Tracert does this 3 times per router Stopping criterion m Echo request eventually arrives at destination host m Destination returns echo reply m When source gets this ICMP, stops. TCP/IP Architecture Advanced Features

11. 11 ICMP: Internet Control Message Protocol r Tracert (Trace route) TCP/IP Architecture Advanced Features

12. 12 ICMP: Internet Control Message Protocol r Destination unreachable (type 3) m Most usual code values (causes) Code 1: host unreachable Code 3: port unreachable Code 4: fragmentation needed TCP/IP Architecture Advanced Features

13. 13 ICMP: Internet Control Message Protocol r ICMP Redirect (type 5) m useful when there are some possible gateways Steps m Packet is sent to default gateway m Default gateway sends packet to router B m Default gateway sends ICMP redirect to host TCP/IP Architecture Advanced Features

14. 14 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

15. 15 Dynamic Address Configuration r Address configuration m static m dynamic: automatic and more efficient r Dynamic Address Configuration Protocols m RARP: Reverse Address Resolution Protocol m BootP: Bootstrap Protocol m DHCP: Dynamic Host Configuration Protocol TCP/IP Architecture Advanced Features

16. 16 Dynamic Address Configuration r RARP m RARP: Reverse Address Resolution Protocol m Given a MAC, an IP address is assigned m Messages have the same structure as ARP ones m RARP is limited and, thus, obsolete. TCP/IP Architecture Advanced Features

17. 17 Dynamic Address Configuration r BootP m BootP Protocol: Bootstrap Protocol m Used to obtain IP automatically (generally in boot process) m Not usually utilized for Dynamic Address Configuration, as DHCP is an improved version of BootP. r BootP process m Host determines its own MAC m Host sends its IP to server’s port 67 (0.0.0.0 if doesn’t know its IP and 255.255.255.255 if doesn’t’ know the server’s one) m Server searches host’s MAC in a configuration file m Server fills server’s and host’s IPs in UDP datagram and sends it to client’s port 68 m Host saves its IP and boots TCP/IP Architecture Advanced Features

18. 18 Dynamic Address Configuration r BootP message m Code: BootPRequest & BootPReply m Transaction id m HW address: e.g. MAC m Server host name (server does not need to be in the same broadcast domain) m Boot file name m Vendor specific area Magic cookie: shows the kind of optional info below A critical field for DHCP TCP/IP Architecture Advanced Features

19. 19 Dynamic Address Configuration r DHCP Dynamic Host Configuration Protocol (DHCP) – RFC 2131: m Capable of automatically assign reusable (IP address leasing) m Based on BootP, standardizing Vendor Specific Area field in BootP PDU (312 bytes). m 3 mechanisms for the assignment of IP addresses: Automatic assignment: –DHCP assigns a permanent IP address to the host. Dynamic assigment: –DHCP assigns an IP address for a limited period of time -> automatic reuse of non- neccessary IP addresses Static assignment: –IP address assigned by network administrator TCP/IP Architecture Advanced Features

20. 20 Dynamic Address Configuration r DHCP message m Same as BootP message except options field (312 bytes) instead of Vendor Specific Area First four bytes: magic cookie -> 99.130.83.99 (means DHCP). Different options. Most important below –50: requested IP address –51: IP address lease time –53: type of DHCP message TCP/IP Architecture Advanced Features

21. 21 Dynamic Address Configuration r DHCP cycle m 1. DHCP DISCOVER: tries to find a DHCP Server. m 2. DHCP OFFER: the server/s offers an IP address m 3. DHCP REQUEST: the client requests some parameters (generally the ones oferred by the server) m 4. DHCP ACK: server ACK Besides : DHCP RELEASE: releases IP address DHCP DECLINE. The offered IP is in use DHCP INFORM: requests some configuration parameters DHCP NAK: if server does not accept request TCP/IP Architecture Advanced Features  Note: Basic cycle is executed if an IP address is not available. Other way, only half the cycle take place.

22. 22 Dynamic Address Configuration r Other DHCP features m A router may be a DHCP server m BootP Relay: when the server is not in the same client’s broadcast domain m Gratuitous ARP: ARP request by the client of its own IP. Checks if the assigned IP is busy. m Option 50: client requests a fixed IP m Option 51: IP address lease time m Maximum DHCP message size: 576 bytes TCP/IP Architecture Advanced Features

23. 23 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

24. 24 Address Translation: NAT r Problem: limited number of IP addr. r Solutions o Subnetting o Private IP addr 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16 TCP/IP Architecture Advanced Features

25. 25 Address Translation: NAT r Private IP addr: how can the dest know whose is the private IP addr? r Solution: NAT (Network Address Translation) o Mechanism used to modify the IP addr inside pkts o Allows private IP addr (inside networks) communication with public IP addr (outside networks) o NAT routers must keep a NAT table with translation in both directions TCP/IP Architecture Advanced Features

26. 26 NAT basic functioning  NAT Router has one or more IP addr for NAT -> for translating private IP into public IP  NAT Router modifies “Source IP addr” field in the IP header & stores matching public & pvt addr in the NAT Table  Dest responds to modified addr  NAT Router searches on its NAT Table & matches public & pvt addr, sending the pkt to the pvt IP TCP/IP Architecture Advanced Features

27. 27 Types of NAT  Dynamic NAT  Static NAT  NAPT (Network Address Port Translation) TCP/IP Architecture Advanced Features

28. 28 Dynamic NAT  Translation is unidirectional  Traffic comes from the inside network  Translation is temporary  Once public IP addr is not in use, it is deleted from NAT Table TCP/IP Architecture Advanced Features

29. 29 Dynamic NAT r Advantage m Saves public IP addr r Disadvantage m Traffic always initiated from the inside network -> does not allow servers TCP/IP Architecture Advanced Features

30. 30 Static NAT r Translations are in the NAT Table since routers are configured r Communication may be initiated by both the inside & the outside networks r Public IP addr must be known (via DNS) by the hosts in the outside network TCP/IP Architecture Advanced Features

31. 31 Static NAT r Advantage m Allows servers r Disadvantage m One public IP addr per pvt IP addr… but both dynamic & static NAT may be used together TCP/IP Architecture Advanced Features

32. 32 NAPT r Transport-Layer Port Identifiers are used r Several pvt IP addr may be translated into a unique public IP addr TCP/IP Architecture Advanced Features

33. 33 About NAT r Not every app work properly when going through a NAT router (e.g, BOOTP) r Difficult to follow the traffic that goes through several NAT routers r NAT increases router processing time r NAPT is a type of NAT -> there are also dynamic NAPT & static NAPT. Both may also be used together TCP/IP Architecture Advanced Features

34. 34 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

35. 35 Routing in the internet r Network layer functions m Addressing m Routing r Routing: finding the BEST route m Best route depends on different criteria: # of hops, transfer rate, load of a link, cost, reliability… m Different routes Link breakage Slow links TCP/IP Architecture Advanced Features

36. 36 Routing in the internet r Two types of protocols m IGP (Interior Gateway Protocols): define routing inside an AS. (RIP, OSPF…) m EGP (Exterior Gateway Protocols): define routing between different AS. Concept: Autonomous System (AS) r AS: IP networks with a common routing management TCP/IP Architecture Advanced Features

37. 37 Routing in the internet Important concepts about routing: r Virtual circuit vs datagrama r Packet flow m Unicast m Broadcast m Multicast r Unicast routing algorithms m Static m Adaptive Centralized Isolated Distributed TCP/IP Architecture Advanced Features

38. 38 Routing in the internet r Two approaches in routing m Virtual circuit Route is established in connection start m Datagram Rcvr addr is inside every packet TCP/IP Architecture Advanced Features

39. 39 Virtual circuit vs. Datagram r Virtual circuit m Error & flow control; order maintenance m Connection oriented Three phases: establishment, transfer & termination m Advantages Efficiency QoS r Datagram m Each packet is an independent unit Dest addr in every packet Packets may arrive disordered to dest No error or flow control m Advantages More simple No connection -> better for short-time tx More reliable Better for heterogeneous networks TCP/IP Architecture Advanced Features

40. 40 Packet flow r Unicast r Broadcast r Multicast TCP/IP Architecture Advanced Features

41. 41 A B C D E F 4 flows 2 flows Unicast r Individual flows: one tx, one rx TCP/IP Architecture Advanced Features

42. 42 Broadcast r one tx, everyone rx A B C D E F 1 flow TCP/IP Architecture Advanced Features

43. 43 Multicast r one flow, only desired rx A B C D E F 1 flow TCP/IP Architecture Advanced Features

44. 44 Unicast routing r Objective m Carry pkts from sender to receiver r Network-layer routing m Hierarchic addressing: first finds network & the host r Routing algorithm m Router calculates the way of routing r Routing algorithm features m Correct m Simple m Robust m Fair m Optimum TCP/IP Architecture Advanced Features

45. 45 Routing algorithms r Router m Network device that interconnects networks & implements routing algorithm m Routing algorithm decides which interface is correct Router Input gateways Output gateways Routing Table Routing Engine TCP/IP Architecture Advanced Features

46. 46 Routing algorithms r Classification m Static routing m Adaptive routing Centralized Isolated Distributed: most used on the internet (RIP/OSPF) TCP/IP Architecture Advanced Features

47. 47 Static Routing r Does not consider current network condition r Routes are determined before starting network service r Advantages m Simple m Good results for constant traffic and network topology r Disadvantages m Not suitable for networks with changing topology m Not suitable for big networks -> not scalable TCP/IP Architecture Advanced Features

48. 48 Adaptive Routing r Decisions based on m Current topology m Network condition (congested links) r Better than static routing but more difficult to implement r Three subgroups m Centralized Adaptive Routing m Isolated Adaptive Routing m Distributed Adaptive Routing TCP/IP Architecture Advanced Features

49. 49 Centralized Adaptive Routing r Routing Control Center (RCC) r Nodes (routers) send info about their condition to RCC m List of neighbour nodes m Queue length m Use of links r RCC m Receives the information m Calculates optimum route for every two nodes m Calculates routing table for every node m Distributes tables to nodes r Disadvantages m RCC & links to RCC -> bottlenecks m Inaccurate calculation TCP/IP Architecture Advanced Features

50. 50 Isolated Adaptive Routing r No info interchange between nodes r Decisions based only on local info -> simple r Example m Flooding TCP/IP Architecture Advanced Features

51. 51 Distributed Adaptive Routing r Used on the internet r Two subgroups m Distance vector algorithms Decisions based on the information received from neighbour nodes E.g. RIP (Routing Information Protocol) m Link state algorithms All the nodes know the state of the network Some time to propagate changes E.g. OSPF (Open Shortest Path First) TCP/IP Architecture Advanced Features

52. 52 RIP: Routing Information Protocol r Routing Information Protocol (RIP) – RFC 1058 (RIP), RFC 1723 (RIPv2): r Routing Protocol (application- layer protocol over UDP – port 520 -) r Used for interior routing inside an AS r RIPv2 is identical to RIP, but with two extensions: m Allows CIDR m Authentication mechanism r Metric: hop counts r Maximum number of hops -> 15 r Better for homogeneous networks r Routing table distance vector-based r Routing table updates: m Periodic updates: via broadcast (in RIPv2: multicast to 224.0.0.9) m Updates when network topology changes TCP/IP Architecture Advanced Features

53. 53 RIP: Routing Information Protocol RIP functioning r Update from neighbour N arrives to a router R: m Networks known by N, and not by R, are included in R’s routing table. m If N knows a better route for a network known by both, R’s routing table is updated m Metric (# of hops) is increased by one m Router R publishes information increasing in one unit what it is introduced in its routing table. m Update messages tx to neighbours. Two ways Not using split horizon technique: Updates are sent to all the neighbours. Using split horizon technique. Updates sent to all the neighbours, except to those who informed about the best route. TCP/IP Architecture Advanced Features

54. 54 RIP: Routing Information Protocol RIP timers r Routing-update timer: 30 seconds – random time r Route-timeout timer: after timeout -> invalid route r Route-flush timer: after timeout -> deletes route from enrouting table TCP/IP Architecture Advanced Features

55. 55 RIP: Routing Information Protocol RIP message r Command m Request (1) m Response (2): most common (updates) r Version: v1 or v2 r RIP version 2: most important field -> subnet mask -> allows CIDR (subnetting) TCP/IP Architecture Advanced Features

56. 56 OSPF: Open Shortest Path First Open Shortest Path First (OSPF) r Used for interior routing inside an AS r Larger networks than RIP (usually) r Open protocol (RFC 2328) TCP/IP Architecture Advanced Features

57. 57 OSPF: Basic Foundations Open Shortest Path First (OSPF) r Link state routing protocol r Dijkstra algorithm to find the BEST route r A router builds a graph r Graph weights are configured by the network administrator m All equal to 1 (similar to RIP) m Inversely proportional to BW (usual criterium) m Any criteria may be fixed Open Shortest Path First (OSPF) r Updates disseminated to entire AS (via flooding) m Changes in topology m Periodically (once every 30 min, at least) r carried in OSPF messages directly over IP (rather than TCP or UDP) -> protocol field: 89 r Link connectivity is checked by HELLO msgs for neighbours TCP/IP Architecture Advanced Features

58. 58 OSPF advanced features (not in RIP) r security: all OSPF messages authenticated r For each link, multiple cost metrics for different TOS r hierarchical OSPF in large domains. TCP/IP Architecture Advanced Features

59. 59 OSPF header r Checksum: error control r Authentication ValueType 1HELLO 2Database description 3Link state request 4Link state update 5Link state ACK TCP/IP Architecture Advanced Features

60. 60 BGP: Border Gateway Protocol r Problem: Different IP networks do not have to use same routing protocol r Two types of protocols m IGP (Interior Gateway Protocols): define routing inside an AS. (RIP, OSPF…) m EGP (Exterior Gateway Protocols): define routing between different AS. r BGP (Border Gateway Protocol): most common EGP (RFC 4271) TCP/IP Architecture Advanced Features

61. 61 BGP: Main features r BGP provides each AS means to: 1. Obtain subnet reachability information from neighboring ASs. 2. Propagate reachability information to all AS- internal routers. r allows subnet to advertise its existence to rest of Internet TCP/IP Architecture Advanced Features

62. 62 BGP: Main features r Every AS: ASN = Autonomous System Number) r Inside every AS -> AS routing protocol r Outside AS -> “border router”: border routers in different AS exchange their routing tables r BGP works over TCP (port 179) TCP/IP Architecture Advanced Features

63. 63 BGP: Example TCP/IP Architecture Advanced Features

64. 64 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

65. 65 Principles of Congestion Control Congestion: r informally: “too many sources sending too much data too fast for network to handle” r different from flow control! r manifestations: m lost packets (buffer overflow at routers) m long delays (queuing in router buffers) TCP/IP Architecture Advanced Features

66. 66 Causes/costs of congestion r Two tx: m IN = Sending rate m OUT = Receiving rate m C= Router capability r Queue theory unlimited shared output link buffers Host A in : original data Host B out r large delays when congested r maximum achievable throughput TCP/IP Architecture Advanced Features

67. 67 r Supposition: Tx retx lost packets r Now, IN is not tx -> higher rate IN ’ r Congestion costs: m more work (retx) m unneeded retransmissions: link carries multiple copies of pkt Causes/costs of congestion: unlimited shared output link buffers Host A in : original data Host B out TCP/IP Architecture Advanced Features

68. 68 Causes/costs of congestion r Two tx and the same dest r Supposition: congestion in the router between A and dest r Another cost of congestion: m when a packet is dropped, any upstream transmission capacity used for that packet was wasted finite shared output link buffers Host A in : original data Host B out ' in : original data, plus retransmitted data TCP/IP Architecture Advanced Features

69. 69 Causes/costs of congestion r Congestion costs: a summary m Big delays when the incoming rate to a router is near to the link capability. m The tx must retx the lost segments due to the router overflow. m Unnecessary BW is used for the retx of duplicated copies of segments (due to delays). m Upstream transmission capacity used for a packet is wasted when it is discarded. TCP/IP Architecture Advanced Features

70. 70 Approaches towards congestion control End-end congestion control: r no explicit feedback from network r congestion inferred from end-system observed loss, delay r approach taken by TCP Network-assisted congestion control: r routers provide feedback to end systems m E.g. single bit indicating congestion Two broad approaches towards congestion control: TCP/IP Architecture Advanced Features

71. 71 TCP Congestion Control r sender limits transmission: LastByteSent-LastByteAcked  CongWin r How does sender perceive congestion? m loss event = timeout or 3 duplicate acks  TCP sender reduces rate ( CongWin ) after loss event Host A timeout Host B time X resend 2 nd segment Host A Seq=92, 8 bytes data ACK=100 loss timeout lost ACK scenario Host B X Seq=92, 8 bytes data ACK= 100 time Resending a segment after triple duplicate ACK TCP/IP Architecture Advanced Features

72. 72 TCP congestion control: additive increase, multiplicative decrease (AIMD) r Approach: increase transmission rate (window size), probing for usable bandwidth, until loss occurs m additive increase: increase CongWin by 1 MSS every RTT until loss detected m multiplicative decrease: cut CongWin in half after loss time congestion window size Saw tooth behavior: probing for bandwidth TCP/IP Architecture Advanced Features

73. 73 TCP Congestion Control: details r Roughly,  When connection begins, CongWin = 1 MSS m Example: MSS = 500 bytes & RTT = 200 ms m initial rate = 20 kbps r three phases: m slow start (SS) m Congestion avoidance (CA): e.g. AIMD m Fast recovery (FR) r First two are compulsory in TCP, while the last one is recommendable rate = CongWin RTT Bytes/sec TCP/IP Architecture Advanced Features

74. 74 TCP Slow Start r available bandwidth may be >> MSS/RTT r When connection begins, increase rate exponentially fast until first loss event r initial rate is slow but ramps up exponentially fast Host A one segment RTT Host B time two segments four segments TCP/IP Architecture Advanced Features

75. 75 Congestion avoidance r After 3 dup ACKs:  CongWin is cut in half m window then grows linearly r But after timeout event:  CongWin instead set to 1 MSS; m window then grows exponentially m to a threshold, then grows linearly  3 dup ACKs indicates network capable of delivering some segments  timeout indicates a “more alarming” congestion scenario Philosophy: TCP/IP Architecture Advanced Features

76. Transport Layer Advanced Features76 Summary: TCP Congestion Control  When CongWin is below Threshold, sender in slow-start phase, window grows exponentially.  When CongWin is above Threshold, sender is in congestion-avoidance phase, window grows linearly.  When a triple duplicate ACK occurs, Threshold set to CongWin/2 and CongWin set to Threshold.  When timeout occurs, Threshold set to CongWin/2 and CongWin is set to 1 MSS. Note: TCP version varies the way congestion control is applied. For example, TCP Tahoe always reduces Congestion Window to its initial value after a loss event. Meanwhile, in TCP Reno, all the congestion phases take place.

77. 77 Chapter 2 outline TCP/IP Architecture Advanced Features r 3.1 IPv4 error control: ICMP r 3.2 IPv4 address dynamic configuration: DHCP r 3.3 Address Translation: NAT r 3.4 Routing in the Internet m RIP m OSPF m BGP r 3.5 TCP congestion control r 3.6 IP version 6

78. 78 IPv6 r Initial motivation: 32-bit address space completely allocated. r Basic changes: m 128-bit address space E.g: 2002:96d6:8ddc::96dc:6301 (the bits remaining are zeros) m header format helps speed processing/forwarding m 40-byte header (fixed size) m Other changes based on previous experience on IPv4 TCP/IP Architecture Advanced Features

79. 79 IPv6 header Version: 6 Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same “flow.” (concept of“flow” not well defined). Payload length: data field length Next header: identify upper layer protocol for data Hop limit: analog to IPv4 TTL field Src & Dest addr: 128 bytes TCP/IP Architecture Advanced Features

80. 80 Changes from IPv4 r Checksum: removed entirely to reduce processing time at each hop r Fragmentation: removed from IPv6, also to reduce processing time r Options: allowed, but outside of header, indicated by “Next Header” field r ICMPv6: new version of ICMP m additional message types, e.g. “Packet Too Big” TCP/IP Architecture Advanced Features

81. 81 Transition from IPv4 to IPv6 r Not all routers can be upgraded simultaneous m no D Day m How does the internet operate with mixed IPv4 and IPv6 routers? r Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers TCP/IP Architecture Advanced Features