3. Internet Protocol: Connectionless Datagram Delivery Introduction
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Introduction Internet architecture and philosophy 3. Internet Protocol: Connectionless Datagram Delivery Application Services Reliable Transport Service Connectionless Packet Delivery Service IP packet delivery service • • • • • 최양희 서울대학교 컴퓨터공학부 1 Unreliable: lost, duplicated, delayed, or delivered out of order Best-effort Connectionless Variable size datagrams Data forwarding only (routing, error, and control by other protocols) 2002 Yanghee Choi IP Features Router Features Interconnecting end systems across multiple networks Implemented everywhere (end system, router) High level protocol data encapsulated in IP Protocol Data Unit (PDU) IP version 4 now in service (rfc 791) IP version 6 (IPv6) is coming (rfc 1883) 2002 Yanghee Choi 2 Coping with the differences among networks • Addressing schemes • Maximum packet size • Hardware and software interfaces • No assumption on network reliability 3 2002 Yanghee Choi 4 1 IP datagram IP encapsulation IP Header HEADER IP Data DATA Frame Header 2002 Yanghee Choi 5 Frame Data 2002 Yanghee Choi Transmission across Internet 6 IP Datagram Forwarding Delivers datagrams to destination subnetwork Routers maintain a routing table of next hops Next hop field does not appear in the datagram Net 1 Table at R2 2002 Yanghee Choi 7 2002 Yanghee Choi R1 Net 2 Destination Net 1 Net 2 Net 3 Net 4 R2 Net 3 R3 Net 4 Next Hop Forward to R1 Deliver Direct Deliver Direct Forward to R3 8 2 Routing Table IPv4 Datagram Format IF ((Mask[I] & Destination_Address) = Destination [I]) Forward to NextHop [I] 30.0.0.7 40.0.0.8 0 4 8 VERS HLEN 128.1.0.9 16 30.0.0.0 R1 Net 2 40.0.0.0 40.0.0.7 R2 Net 3 128.1.0.0 128.1.0.8 R3 Net 4 FLAGS TIME TO LIVE PROTOCOL 192.4.0.0 192.4.10.9 24 31 TOTAL LENGTH IDENTIFICATION Net 1 19 SERVICE TYPE FRAGMENT OFFSET HEADER CHECKSUM SOURCE IP ADDRESS DESTINATION IP ADDRESS Destination 30.0.0.0 40.0.0.0 128.1.0.0 192.4.10.0 Mask 255.0.0.0 255.0.0.0 255.255.0.0 255.255.255.0 Next Hop 40.0.0.7 Deliver Direct Deliver Direct 128.1.0.9 2002 Yanghee Choi IP OPTIONS (IF ANY) ... 9 2002 Yanghee Choi IP Format 10 IP Format (cont’d) Version (4 bits) Internet Header Length (4 bits) : in 32-bit words Min header is 5 words Type of Service (8 bits) Precedence, delay, reliability, throughput Total Length (16 bits) header + data in bytes, less than 64KB Identifier (16 bits) uniquely identifies the datagram during its life Flags (3 bits) More flag, No fragmentation Fragment offset (13 bits) in units of 8 bytes Time to live (8 bits) in router hops 2002 Yanghee Choi PADDING DATA Protocol (8 bits) Next level protocol to receive the data Header Checksum (16 bits) One’s complement sum of all 16-bit words in the header Source Address (32 bits) Original source. Does not change along the path Destination Address (32 bits) Final destination. Does not change among the path Options (variable) Padding (variable) Makes header length a multiple of 4 bytes, zero is inserted Data (variable) Data + header < 65,535 bytes 11 2002 Yanghee Choi 12 3 Service Type 0 1 2 PRECEDENCE 3 4 5 D T R 6 DiffServ 7 0 UNUSED 7 Unused CODEPOINT D low delay T high throughput R high reliability Precedence=importance of datagram ===> hint to routing algorithm 2002 Yanghee Choi 6 5 64 different services xxx000 for original definition precedence 6 or 7 for routing traffic 13 2002 Yanghee Choi 14 Fragmentation Fragmentation Datagram Size, Network MTU, and Fragmentation • MTU (maximum Transfer Unit): fixed upper bound on the amount data that can be transferred in one physical frame e.g.) Ethernet: 1500 octets, FDDI: 4470 octets • Fragmentation: dividing large datagrams into smaller pieces when the datagram needs to traverse a network that has a small MTU • Fragments must be reassembled at the destination • If any fragments are lost, the datagram cannot be reassembled. • Reassembly timer : if expired, discard the received packets Fragmentation control HOST A HOST B Net 1 MTU=1500 R1 • IDENTIFICATION : identical to the fragments • FLAGS: Don’t Fragment bit, More Fragments bit, • FRAGMENT OFFSET : by 8 octets Net 2 MTU=620 R2 Net 3 MTU=1500 No sequence number 2002 Yanghee Choi 15 2002 Yanghee Choi 16 4 Fragments Datagram Header Data1 600 octets Internet Datagram Options Included primarily for network testing or debugging Type(code)- Length-Value Option code (1 octet) Data2 Data3 600 octets 200 octets 0 1 2 3 COPY OPTION CLASS Fragment 1 Data1 Header 600 octets Fragment 1 (offset 0) Fragment 2 Data2 Header 600 octets Fragment 2 (offset 600) Fragment 3 Data3 Header 200 octets Fragment 3 (offset 1200) 2002 Yanghee Choi 17 4 5 6 7 OPTION NUMBER Copy = 1 option copied to all fragments =0 copied to the first fragment only Class = 0 Datagram or network control =1 Resv’d =2 Debugging and measurement =3 Resv’d Option length (1 octet) Value : variable length 2002 Yanghee Choi IP Options 18 Record Route Option Loose Source Routing Record Route Strict Source Routing 0 8 16 24 31 CODE LENGTH POINTER FIRST IP ADDRESS Internet Timestamp etc. SECOND IP ADDRESS ……... 2002 Yanghee Choi 19 2002 Yanghee Choi 20 5 Strict Source Route Option 0 8 16 24 Timestamp Option 31 0 24 IP ADDRESS OF FIRST HOP FIRST IP ADDRESS IP ADDRESS OF SECOND HOP FIRST TIMESTAMP ……... 2002 Yanghee Choi 31 ……... In msec since midnight OFLOW : count of routers that couldn’t supply timestamps because the option was too small FLAGS : record timestamps only (0), etc. Addresses overwritten by visited routers (= record route) 21 2002 Yanghee Choi IPv6 22 IPv6 Addresses Expanded Addressing Capabilities Flexible header format Improved Support for Extensions and Options Support for resource allocation Provision for protocol extension Flow Labeling Capability Authentication and Privacy Capabilities 2002 Yanghee Choi 16 CODE LENGTH POINTER OFLOW FLAGS CODE LENGTH POINTER 8 23 128-bit long. Fixed size 3.4 X 10~38 addresses Assigned to individual interfaces Allows multiple interfaces per host Allows multiple addresses per interface Allows unicast, multicast, anycast Allows provider based, site-local, link-local 85% of the space is unassigned 2002 Yanghee Choi 24 6 Colon-Hex Notation IPv6 Prefix Allocation Dot-Decimal 147.47.114.115 Colon-Hex FEDC:0000:0000:0000:3232:0000:0000:ACFE 2002 Yanghee Choi 25 Allocation Prefix Allocation Prefix Reserved Unassigned NSAP IPX Unassigned Unassigned Unassigned Global Unicast Unassigned Unassigned Unassigned 0000 0000 0000 0001 0000 001 0000 010 0000 011 0000 1 0001 001 010 011 100 Unassigned Unassigned Unassigned Unassigned Unassigned Unassigned Unassigned Unassigned Link-Local Site-Local Multicast 101 110 1110 1111 0 1111 10 1111 110 1111 1110 1111 1110 0 1111 1110 10 1111 1110 11 1111 1111 2002 Yanghee Choi IPv6 Address Formats 26 Local Address Top-Level Aggregation (ISP or exchange) Next-Level Aggregation (subscriber site) Site-Level Aggregation (subnet) 1111111010 Interface ID Link Local address : Not forwarded outside the link 001 TLA id RES 3 13 8 NLA id 24 SLA id INTERFACE id 16 1111111011 Interface ID Site Local address : Not forwarded outside the subnetwork 64 Aggregatable global unicast address 2002 Yanghee Choi 27 2002 Yanghee Choi 28 7 IPv4 Addresses Anycast Address 32 0000…………………………………………...…………………..0000 IPv4 address Routed to the nearest interface in the group Allocated in the unicast address space 0000…………………………………………...…………………..FFFF IPv4 address Subnet-router anycast address : delivered to one router in the subnetwork IPv4-compatible IPv6 address 2002 Yanghee Choi 29 2002 Yanghee Choi Multicast Addresses IPv6 PDU General Form Flag bit : T=0 Permanent (well-known) multicast address T=1 Transient Scope 1 Node-local 2 Link-local 5 Site-local 8 Organization-local E Global Group ID Predefined 1 All nodes 2 Routers 1:0 DHCP servers 11111111 Flag Scope 2002 Yanghee Choi 30 40 octets IPv6 header 0 or more Extension header ….. Extension Transport-level header PDU Group ID 31 2002 Yanghee Choi 32 8 IPv6 Header 4 8 Version traffic class Payload length 16 24 Flow label 31 Next header Hop limit Source Address 40 octets 0 IPv6 Header Destination Address 2002 Yanghee Choi 33 Version = 6 Traffic Class (4 bits) Flow Label (24 bits) Payload length (16 bits) : in octets except the IPv6 header Next Header (8 bits) : identifies the type of header following the IPv6 header Hop Limit (8 bits) : remaining number of allowable hops for this packet Source Address (128 bits) Destination Address (128 bits) : may not be the ultimate destination, if routing header is present 40 octets in length 2002 Yanghee Choi Traffic Class 34 Traffic Class Congestion-Controlled Traffic Class : variable delay, out-of-order packet reception is acceptable. Non-Congestion-Controlled Traffic : constant data rate, and delay like realtime video and audio 8 levels of priorities : 8 (lowest) - 15 (highest) • Internet Control Traffic (most important traffic) : routing info • Interactive Traffic : on-line user-to-host • Attended Bulk Transfer : FTP, HTTP • Unattended Data Transfer : E-mail • Filler Traffic : handled in the background, USENET • Uncharacterized Traffic 2002 Yanghee Choi 35 2002 Yanghee Choi 36 9 Flow Label Header Order A Flow is uniquely identified by source address and 24-bit flow label. A flow may comprise single or multiple TCP connections. A single application may generate a single or multiple flows (multimedia conferencing). At router, the same flow has the same path, resource allocation, discard requirements, accounting, and security attributes. 2002 Yanghee Choi 37 IPv6 header : mandatory Hop-by-Hop Options header Destination Options header to be processed by destinations in the IPv6 header and Routing header Routing header : extended routing (source routing) Fragment header Authentication header Encapsulating Security Payload header Destination Options header to be processed by destination in the IPv6 header upper-layer header (TCP, application etc.) 2002 Yanghee Choi IPv6 Fragmentation 38 IPv6 Transition (ngtrans) End-to-end Does not accommodate route changes Use Path MTU Discovery to determine minimum MTU in the path Minimum MTU is 1280 octets IPv4/IPv6 DualStack IPv4 IPv6 IPv6 IPv4 IPv6-in-IPv4 tunneling IPv4 IPv4/IPv6 Translation 2002 Yanghee Choi 39 2002 Yanghee Choi IPv6 40 10
