TCP/IP Tutorial and Technical Overview - IBM

TCP/IP Tutorial and Technical OverviewLydia Parziale David T. Britt Chuck Davis
Jason Forrester Wei Liu
Carolyn Matthews Nicolas Rosselot
Introduces advanced concepts and new technologies
Includes the latest TCP/IP protocols
Front cover
December 2006
© Copyright International Business Machines Corporation 1989-2006. All rights reserved. Note to U.S. Government Users Restricted Rights -- Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
Eighth Edition (December 2006)
Note: Before using this information and the product it supports, read the information in “Notices” on page xvii.
Contents
Notices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Trademarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix The team that wrote this redbook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx Become a published author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxii Comments welcome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
Part 1. Core TCP/IP protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 1. Architecture, history, standards, and trends . . . . . . . . . . . . . . . 3 1.1 TCP/IP architectural model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.1 Internetworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1.2 The TCP/IP protocol layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1.3 TCP/IP applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 The roots of the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.2.1 ARPANET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.2.2 NSFNET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.3 Commercial use of the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.4 Internet2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.2.5 The Open Systems Interconnection (OSI) Reference Model . . . . . . 20
1.3 TCP/IP standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.3.1 Request for Comments (RFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 1.3.2 Internet standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.4 Future of the Internet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.1 Multimedia applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.2 Commercial use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.3 The wireless Internet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.5 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Chapter 2. Network interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.1 Ethernet and IEEE 802 local area networks (LANs) . . . . . . . . . . . . . . . . . 30
2.1.1 Gigabit Ethernet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.2 Fiber Distributed Data Interface (FDDI). . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3 Serial Line IP (SLIP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.4 Point-to-Point Protocol (PPP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.1 Point-to-point encapsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.5 Integrated Services Digital Network (ISDN) . . . . . . . . . . . . . . . . . . . . . . . 38 2.6 X.25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
© Copyright IBM Corp. 1989-2006. All rights reserved. iii
2.7 Frame relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.7.1 Frame format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.7.2 Interconnect issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.7.3 Data link layer parameter negotiation . . . . . . . . . . . . . . . . . . . . . . . . 43 2.7.4 IP over frame relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.8 PPP over SONET and SDH circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.8.1 Physical layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.9 Multi-Path Channel+ (MPC+) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.10 Asynchronous transfer mode (ATM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
2.10.1 Address resolution (ATMARP and InATMARP) . . . . . . . . . . . . . . . 47 2.10.2 Classical IP over ATM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.10.3 ATM LAN emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.10.4 Classical IP over ATM versus LAN emulation. . . . . . . . . . . . . . . . . 59
2.11 Multiprotocol over ATM (MPOA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 2.11.1 Benefits of MPOA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 2.11.2 MPOA logical components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 2.11.3 MPOA functional components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 2.11.4 MPOA operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.12 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Chapter 3. Internetworking protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.1 Internet Protocol (IP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.1.1 IP addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.1.2 IP subnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.1.3 IP routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.1.4 Methods of delivery: Unicast, broadcast, multicast, and anycast . . . 84 3.1.5 The IP address exhaustion problem . . . . . . . . . . . . . . . . . . . . . . . . . 86 3.1.6 Intranets: Private IP addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 3.1.7 Network Address Translation (NAT) . . . . . . . . . . . . . . . . . . . . . . . . . 89 3.1.8 Classless Inter-Domain Routing (CIDR) . . . . . . . . . . . . . . . . . . . . . . 95 3.1.9 IP datagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
3.2 Internet Control Message Protocol (ICMP) . . . . . . . . . . . . . . . . . . . . . . . 109 3.2.1 ICMP messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 3.2.2 ICMP applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
3.3 Internet Group Management Protocol (IGMP) . . . . . . . . . . . . . . . . . . . . 119 3.4 Address Resolution Protocol (ARP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
3.4.1 ARP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.4.2 ARP detailed concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.4.3 ARP and subnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 3.4.4 Proxy-ARP or transparent subnetting . . . . . . . . . . . . . . . . . . . . . . . 123
3.5 Reverse Address Resolution Protocol (RARP) . . . . . . . . . . . . . . . . . . . . 124 3.5.1 RARP concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
3.6 Bootstrap Protocol (BOOTP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
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3.6.1 BOOTP forwarding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 3.6.2 BOOTP considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
3.7 Dynamic Host Configuration Protocol (DHCP) . . . . . . . . . . . . . . . . . . . . 130 3.7.1 The DHCP message format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 3.7.2 DHCP message types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 3.7.3 Allocating a new network address. . . . . . . . . . . . . . . . . . . . . . . . . . 134 3.7.4 DHCP lease renewal process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 3.7.5 Reusing a previously allocated network address . . . . . . . . . . . . . . 138 3.7.6 Configuration parameters repository. . . . . . . . . . . . . . . . . . . . . . . . 139 3.7.7 DHCP considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 3.7.8 BOOTP and DHCP interoperability . . . . . . . . . . . . . . . . . . . . . . . . . 140
Chapter 4. Transport layer protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 4.1 Ports and sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
4.1.1 Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 4.1.2 Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
4.2 User Datagram Protocol (UDP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 4.2.1 UDP datagram format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 4.2.2 UDP application programming interface . . . . . . . . . . . . . . . . . . . . . 149
4.3 Transmission Control Protocol (TCP) . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 4.3.1 TCP concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 4.3.2 TCP application programming interface . . . . . . . . . . . . . . . . . . . . . 164 4.3.3 TCP congestion control algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 165
Chapter 5. Routing protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 5.1 Autonomous systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 5.2 Types of IP routing and IP routing algorithms . . . . . . . . . . . . . . . . . . . . . 174
5.2.1 Static routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 5.2.2 Distance vector routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 5.2.3 Link state routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 5.2.4 Path vector routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 5.2.5 Hybrid routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
5.3 Routing Information Protocol (RIP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 5.3.1 RIP packet types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 5.3.2 RIP packet format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 5.3.3 RIP modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 5.3.4 Calculating distance vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 5.3.5 Convergence and counting to infinity . . . . . . . . . . . . . . . . . . . . . . . 185 5.3.6 RIP limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
5.4 Routing Information Protocol Version 2 (RIP-2) . . . . . . . . . . . . . . . . . . . 189 5.4.1 RIP-2 packet format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
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5.4.2 RIP-2 limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 5.5 RIPng for IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
5.5.1 Differences between RIPng and RIP-2 . . . . . . . . . . . . . . . . . . . . . . 193 5.5.2 RIPng packet format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
5.6 Open Shortest Path First (OSPF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 5.6.1 OSPF terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 5.6.2 Neighbor communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 5.6.3 OSPF neighbor state machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 5.6.4 OSPF route redistribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 5.6.5 OSPF stub areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 5.6.6 OSPF route summarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
5.7 Enhanced Interior Gateway Routing Protocol (EIGRP). . . . . . . . . . . . . . 212 5.7.1 Features of EIGRP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 5.7.2 EIGRP packet types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
5.8 Exterior Gateway Protocol (EGP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 5.9 Border Gateway Protocol (BGP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
5.9.1 BGP concepts and terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 5.9.2 IBGP and EBGP communication . . . . . . . . . . . . . . . . . . . . . . . . . . 218 5.9.3 Protocol description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 5.9.4 Path selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 5.9.5 BGP synchronization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 5.9.6 BGP aggregation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 5.9.7 BGP confederations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 5.9.8 BGP route reflectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
5.10 Routing protocol selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 5.11 Additional functions performed by the router. . . . . . . . . . . . . . . . . . . . . 234 5.12 Routing processes in UNIX-based systems . . . . . . . . . . . . . . . . . . . . . 235 5.13 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Chapter 6. IP multicast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 6.1 Multicast addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
6.1.1 Multicasting on a single physical network . . . . . . . . . . . . . . . . . . . . 238 6.1.2 Multicasting between network segments . . . . . . . . . . . . . . . . . . . . 240
6.2 Internet Group Management Protocol (IGMP) . . . . . . . . . . . . . . . . . . . . 241 6.2.1 IGMP messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 6.2.2 IGMP operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
6.3 Multicast delivery tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 6.4 Multicast forwarding algorithms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
6.4.1 Reverse path forwarding algorithm . . . . . . . . . . . . . . . . . . . . . . . . . 252 6.4.2 Center-based tree algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 6.4.3 Multicast routing protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
6.5 Distance Vector Multicast Routing Protocol (DVMRP) . . . . . . . . . . . . . . 254 6.5.1 Protocol overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
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6.5.2 Building and maintaining multicast delivery trees . . . . . . . . . . . . . . 256 6.5.3 DVMRP tunnels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
6.6 Multicast OSPF (MOSPF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 6.6.1 Protocol overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 6.6.2 MOSPF and multiple OSPF areas . . . . . . . . . . . . . . . . . . . . . . . . . 260 6.6.3 MOSPF and multiple autonomous systems . . . . . . . . . . . . . . . . . . 260 6.6.4 MOSPF interoperability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
6.7 Protocol Independent Multicast (PIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 6.7.1 PIM dense mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 6.7.2 PIM sparse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
6.8 Interconnecting multicast domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 6.8.1 Multicast Source Discovery Protocol (MSDP). . . . . . . . . . . . . . . . . 266 6.8.2 Border Gateway Multicast Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 269
6.9 The multicast backbone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 6.9.1 MBONE routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 6.9.2 Multicast applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
6.10 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
Chapter 7. Mobile IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 7.1 Mobile IP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
7.1.1 Mobile IP operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 7.1.2 Mobility agent advertisement extensions . . . . . . . . . . . . . . . . . . . . 278
7.2 Mobile IP registration process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 7.2.1 Tunneling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 7.2.2 Broadcast datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 7.2.3 Move detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 7.2.4 Returning home. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 7.2.5 ARP considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 7.2.6 Mobile IP security considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 286
Chapter 8. Quality of service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 8.1 Why QoS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 8.2 Integrated Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
8.2.1 Service classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 8.2.2 Controlled Load Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 8.2.3 Guaranteed Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 8.2.4 The Resource Reservation Protocol (RSVP) . . . . . . . . . . . . . . . . . 296 8.2.5 Integrated Services outlook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
8.3 Differentiated Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 8.3.1 Differentiated Services architecture . . . . . . . . . . . . . . . . . . . . . . . . 310 8.3.2 Organization of the DSCP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 8.3.3 Configuration and administration of DS with LDAP. . . . . . . . . . . . . 322
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Chapter 9. IP version 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 9.1 IPv6 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
9.1.1 IP growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 9.1.2 IPv6 feature overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
9.2 The IPv6 header format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 9.2.1 Extension headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 9.2.2 IPv6 addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 9.2.3 Traffic class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 9.2.4 Flow labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346 9.2.5 IPv6 security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 9.2.6 Packet sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
9.3 Internet Control Message Protocol Version 6 (ICMPv6) . . . . . . . . . . . . . 352 9.3.1 Neighbor discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353 9.3.2 Multicast Listener Discovery (MLD) . . . . . . . . . . . . . . . . . . . . . . . . 365
9.4 DNS in IPv6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 9.4.1 Format of IPv6 resource records. . . . . . . . . . . . . . . . . . . . . . . . . . . 368
9.5 DHCP in IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 9.5.1 DHCPv6 messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
9.6 IPv6 mobility support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 9.7 IPv6 new opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
9.7.1 New infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 9.7.2 New services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 9.7.3 New research and development platforms . . . . . . . . . . . . . . . . . . . 378
9.8 Internet transition: Migrating from IPv4 to IPv6 . . . . . . . . . . . . . . . . . . . . 379 9.8.1 Dual IP stack implementation: The IPv6/IPv4 node . . . . . . . . . . . . 380 9.8.2 Tunneling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381 9.8.3 Interoperability summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
Chapter 10. Wireless IP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 10.1 Wireless concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 10.2 Why wireless? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
10.2.1 Deployment and cost effectiveness . . . . . . . . . . . . . . . . . . . . . . . 395 10.2.2 Reachability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 10.2.3 Scalability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 10.2.4 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 10.2.5 Connectivity and reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
10.3 WiFi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 10.4 WiMax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 10.5 Applications of wireless networking. . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
10.5.1 Last mile connectivity in broadband services . . . . . . . . . . . . . . . . 402
viii TCP/IP Tutorial and Technical Overview
10.5.2 Hotspots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 10.5.3 Mesh networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
10.6 IEEE standards relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . 403
Part 2. TCP/IP application protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Chapter 11. Application structure and programming interfaces . . . . . . 407 11.1 Characteristics of applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
11.1.1 The client/server model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 11.2 Application programming interfaces (APIs) . . . . . . . . . . . . . . . . . . . . . . 410
11.2.1 The socket API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 11.2.2 Remote Procedure Call (RPC) . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 11.2.3 The SNMP distributed programming interface (SNMP DPI) . . . . . 419 11.2.4 REXX sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Chapter 12. Directory and naming protocols . . . . . . . . . . . . . . . . . . . . . . 425 12.1 Domain Name System (DNS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
12.1.1 The hierarchical namespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 12.1.2 Fully qualified domain names (FQDNs) . . . . . . . . . . . . . . . . . . . . 428 12.1.3 Generic domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428 12.1.4 Country domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 12.1.5 Mapping domain names to IP addresses . . . . . . . . . . . . . . . . . . . 429 12.1.6 Mapping IP addresses to domain names: Pointer queries . . . . . . 430 12.1.7 The distributed name space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 12.1.8 Domain name resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 12.1.9 Domain Name System resource records . . . . . . . . . . . . . . . . . . . 436 12.1.10 Domain Name System messages. . . . . . . . . . . . . . . . . . . . . . . . 439 12.1.11 A simple scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 12.1.12 Extended scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 12.1.13 Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 12.1.14 DNS applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
12.2 Dynamic Domain Name System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 12.2.1 Dynamic updates in the DDNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 454 12.2.2 Incremental zone transfers in DDNS. . . . . . . . . . . . . . . . . . . . . . . 456 12.2.3 Prompt notification of zone transfer . . . . . . . . . . . . . . . . . . . . . . . 457
12.3 Network Information System (NIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458 12.4 Lightweight Directory Access Protocol (LDAP) . . . . . . . . . . . . . . . . . . . 459
12.4.1 LDAP: Lightweight access to X.500 . . . . . . . . . . . . . . . . . . . . . . . 460 12.4.2 The LDAP directory server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 12.4.3 Overview of LDAP architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 12.4.4 LDAP models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 12.4.5 LDAP security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 12.4.6 LDAP URLs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
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12.4.7 LDAP and DCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 12.4.8 The Directory-Enabled Networks (DEN) initiative . . . . . . . . . . . . . 477 12.4.9 Web-Based Enterprise Management (WBEM) . . . . . . . . . . . . . . . 478
Chapter 13. Remote execution and distributed computing. . . . . . . . . . . 483 13.1 Telnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
13.1.1 Telnet operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484 13.1.2 Network Virtual Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485 13.1.3 Telnet options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487 13.1.4 Telnet command structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 13.1.5 Option negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491 13.1.6 Telnet basic commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 13.1.7 Terminal emulation (Telnet 3270) . . . . . . . . . . . . . . . . . . . . . . . . . 492 13.1.8 TN3270 enhancements (TN3270E) . . . . . . . . . . . . . . . . . . . . . . . 493 13.1.9 Device-type negotiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
13.2 Remote Execution Command protocol (REXEC and RSH) . . . . . . . . . 495 13.3 Introduction to the Distributed Computing Environment (DCE). . . . . . . 496
13.3.1 DCE directory service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498 13.3.2 Authentication service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502 13.3.3 DCE threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 13.3.4 Distributed Time Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 13.3.5 Additional information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
13.4 Distributed File Service (DFS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 13.4.1 File naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510 13.4.2 DFS performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
Chapter 14. File-related protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 14.1 File Transfer Protocol (FTP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
14.1.1 An overview of FTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514 14.1.2 FTP operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 14.1.3 The active data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 14.1.4 The passive data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 14.1.5 Using proxy transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 14.1.6 Reply codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523 14.1.7 Anonymous FTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 14.1.8 Using FTP with IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 14.1.9 Securing FTP sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
14.2 Trivial File Transfer Protocol (TFTP) . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 14.2.1 TFTP usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 14.2.2 Protocol description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 14.2.3 TFTP packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
x TCP/IP Tutorial and Technical Overview
14.2.4 Data modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 14.2.5 TFTP multicast option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 14.2.6 Security issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
14.3 Secure Copy Protocol (SCP) and SSH FTP (SFTP). . . . . . . . . . . . . . . 533 14.3.1 SCP syntax and usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 14.3.2 SFTP syntax and usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 14.3.3 SFTP interactive commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
14.4 Network File System (NFS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538 14.4.1 NFS concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538 14.4.2 File integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 14.4.3 Lock Manager protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 14.4.4 NFS file system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 14.4.5 NFS version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 14.4.6 Cache File System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 14.4.7 WebNFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
14.5 The Andrew File System (AFS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 14.6 Common Internet File System (CIFS) . . . . . . . . . . . . . . . . . . . . . . . . . . 548
14.6.1 NetBIOS over TCP/IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548 14.6.2 SMB/CIFS specifics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
Chapter 15. Mail applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555 15.1 Simple Mail Transfer Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
15.1.1 How SMTP works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559 15.1.2 SMTP and the Domain Name System . . . . . . . . . . . . . . . . . . . . . 565
15.2 Sendmail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 15.2.1 Sendmail as a mail transfer agent (MTA) . . . . . . . . . . . . . . . . . . . 568 15.2.2 How sendmail works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
15.3 Multipurpose Internet Mail Extensions (MIME) . . . . . . . . . . . . . . . . . . . 571 15.3.1 How MIME works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574 15.3.2 The Content-Transfer-Encoding field . . . . . . . . . . . . . . . . . . . . . . 582 15.3.3 Using non-ASCII characters in message headers . . . . . . . . . . . . 587
15.4 Post Office Protocol (POP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 15.4.1 Connection states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 15.4.2 POP3 commands and responses . . . . . . . . . . . . . . . . . . . . . . . . . 590
15.5 Internet Message Access Protocol (IMAP4) . . . . . . . . . . . . . . . . . . . . . 591 15.5.1 Fundamental IMAP4 electronic mail models. . . . . . . . . . . . . . . . . 591 15.5.2 IMAP4 states. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 15.5.3 IMAP4 commands and response interaction . . . . . . . . . . . . . . . . 594 15.5.4 IMAP4 messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
Chapter 16. The Web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
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16.1 Web browsers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603 16.2 Web servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 16.3 Hypertext Transfer Protocol (HTTP) . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
16.3.1 Overview of HTTP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 16.3.2 HTTP operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606
16.4 Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615 16.4.1 Static content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615 16.4.2 Client-side dynamic content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616 16.4.3 Server-side dynamic content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617 16.4.4 Developing content with IBM Web application servers . . . . . . . . . 621
Chapter 17. Network management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623 17.1 The Simple Network Management Protocol (SNMP) . . . . . . . . . . . . . . 624
17.1.1 The Management Information Base (MIB) . . . . . . . . . . . . . . . . . . 625 17.1.2 The SNMP agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630 17.1.3 The SNMP manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 17.1.4 The SNMP subagent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 17.1.5 The SNMP model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 17.1.6 SNMP traps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638 17.1.7 SNMP versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639 17.1.8 Single authentication and privacy protocol . . . . . . . . . . . . . . . . . . 647
17.2 The NETSTAT utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648 17.2.1 Common NETSTAT options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649 17.2.2 Sample NETSTAT report output . . . . . . . . . . . . . . . . . . . . . . . . . . 649
Chapter 18. Wireless Application Protocol . . . . . . . . . . . . . . . . . . . . . . . . 655 18.1 The WAP environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657 18.2 Key elements of the WAP specifications. . . . . . . . . . . . . . . . . . . . . . . . 657 18.3 WAP architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658 18.4 Client identifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663 18.5 Multimedia messaging system (MMS) . . . . . . . . . . . . . . . . . . . . . . . . . 663 18.6 WAP push architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
18.6.1 Push framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664 18.6.2 Push proxy gateway (PPG). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665 18.6.3 Push access control protocol (PAP) . . . . . . . . . . . . . . . . . . . . . . . 667 18.6.4 Service indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668 18.6.5 Push over-the-air protocol (OTA) . . . . . . . . . . . . . . . . . . . . . . . . . 668 18.6.6 Client-side infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668 18.6.7 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
18.7 The Wireless Application Environment (WAE2) . . . . . . . . . . . . . . . . . . 670 18.8 User Agent Profile (UAProf) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
xii TCP/IP Tutorial and Technical Overview
18.9 Wireless protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672 18.9.1 Wireless Datagram Protocol (WDP) . . . . . . . . . . . . . . . . . . . . . . . 672 18.9.2 Wireless Profiled Transmission Control Protocol (WP-TCP) . . . . 674 18.9.3 Wireless Control Message Protocol (WCMP) . . . . . . . . . . . . . . . . 678 18.9.4 Wireless Transaction Protocol (WTP) . . . . . . . . . . . . . . . . . . . . . . 679 18.9.5 Wireless Session Protocol (WSP). . . . . . . . . . . . . . . . . . . . . . . . . 682 18.9.6 Wireless profiled HTTP (W-HTTP) . . . . . . . . . . . . . . . . . . . . . . . . 695
18.10 Wireless security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696 18.10.1 Wireless Transport Layer Security (WTLS). . . . . . . . . . . . . . . . . 696 18.10.2 Wireless Identity Module (WIM) . . . . . . . . . . . . . . . . . . . . . . . . . 701
18.11 Wireless Telephony Application (WTA). . . . . . . . . . . . . . . . . . . . . . . . 702 18.12 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 18.13 Specifications relevant to this chapter. . . . . . . . . . . . . . . . . . . . . . . . . 703
Chapter 19. Presence over IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 19.1 Overview of the presence service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710 19.2 Presence Information Data Format (PIDF) . . . . . . . . . . . . . . . . . . . . . . 714 19.3 Presence protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
19.3.1 Binding to TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718 19.3.2 Address resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
Part 3. Advanced concepts and new technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721
Chapter 20. Voice over Internet Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 723 20.1 Voice over IP (VoIP) introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
20.1.1 Benefits and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724 20.1.2 VoIP functional components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 726
20.2 Session Initiation Protocol (SIP) technologies. . . . . . . . . . . . . . . . . . . . 730 20.2.1 SIP request and response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732 20.2.2 Sample SIP message flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733 20.2.3 SIP protocol architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
20.3 Media Gateway Control Protocol (MGCP) . . . . . . . . . . . . . . . . . . . . . . 736 20.3.1 MGCP architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737 20.3.2 MGCP primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
20.4 Media Gateway Controller (Megaco). . . . . . . . . . . . . . . . . . . . . . . . . . . 738 20.4.1 Megaco architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
20.5 ITU-T recommendation H.323. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739 20.5.1 H.323 architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739 20.5.2 H.323 protocol stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741
20.6 Summary of VoIP protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742 20.7 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
Chapter 21. Internet Protocol Television. . . . . . . . . . . . . . . . . . . . . . . . . . 745
Contents xiii
21.1 IPTV overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746 21.1.1 IPTV requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747 21.1.2 Business benefits and applications . . . . . . . . . . . . . . . . . . . . . . . . 749
21.2 Functional components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750 21.2.1 Content acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750 21.2.2 CODEC (encode and decode) . . . . . . . . . . . . . . . . . . . . . . . . . . . 750 21.2.3 Display devices and control gateway . . . . . . . . . . . . . . . . . . . . . . 751 21.2.4 IP (TV) transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
21.3 IPTV technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752 21.3.1 Summary of protocol standards . . . . . . . . . . . . . . . . . . . . . . . . . . 753 21.3.2 Stream Control Transmission Protocol . . . . . . . . . . . . . . . . . . . . . 753 21.3.3 Session Description Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754 21.3.4 Real-Time Transport Protocol (RTP) . . . . . . . . . . . . . . . . . . . . . . 756 21.3.5 Real-Time Control Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762 21.3.6 Moving Picture Experts Group (MPEG) standards . . . . . . . . . . . . 767 21.3.7 H.261. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
Chapter 22. TCP/IP security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771 22.1 Security exposures and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
22.1.1 Common attacks against security . . . . . . . . . . . . . . . . . . . . . . . . . 772 22.1.2 Solutions to network security problems. . . . . . . . . . . . . . . . . . . . . 772 22.1.3 Implementations of security solutions . . . . . . . . . . . . . . . . . . . . . . 774 22.1.4 Network security policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
22.2 A short introduction to cryptography . . . . . . . . . . . . . . . . . . . . . . . . . . . 777 22.2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777 22.2.2 Symmetric or secret-key algorithms . . . . . . . . . . . . . . . . . . . . . . . 779 22.2.3 Asymmetric or public key algorithms. . . . . . . . . . . . . . . . . . . . . . . 780 22.2.4 Hash functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785 22.2.5 Digital certificates and certification authorities . . . . . . . . . . . . . . . 791 22.2.6 Random-number generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792 22.2.7 Export/import restrictions on cryptography . . . . . . . . . . . . . . . . . . 793
22.3 Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 22.3.1 Firewall concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 22.3.2 Components of a firewall system . . . . . . . . . . . . . . . . . . . . . . . . . 796 22.3.3 Types of firewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
22.4 IP Security Architecture (IPSec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809 22.4.1 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810 22.4.2 Authentication Header (AH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813 22.4.3 Encapsulating Security Payload (ESP) . . . . . . . . . . . . . . . . . . . . . 817 22.4.4 Combining IPSec protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823 22.4.5 Internet Key Exchange (IKE) protocol . . . . . . . . . . . . . . . . . . . . . . 829
22.5 SOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
xiv TCP/IP Tutorial and Technical Overview
22.5.1 SOCKS Version 5 (SOCKSv5) . . . . . . . . . . . . . . . . . . . . . . . . . . . 848 22.6 Secure Shell (1 and 2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
22.6.1 SSH overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853 22.7 Secure Sockets Layer (SSL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
22.7.1 SSL overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854 22.7.2 SSL protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856
22.8 Transport Layer Security (TLS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861 22.9 Secure Multipurpose Internet Mail Extension (S-MIME) . . . . . . . . . . . . 861 22.10 Virtual private networks (VPNs) overview . . . . . . . . . . . . . . . . . . . . . . 861
22.10.1 VPN introduction and benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . 862 22.11 Kerberos authentication and authorization system . . . . . . . . . . . . . . . 864
22.11.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865 22.11.2 Naming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865 22.11.3 Kerberos authentication process. . . . . . . . . . . . . . . . . . . . . . . . . 866 22.11.4 Kerberos database management . . . . . . . . . . . . . . . . . . . . . . . . 870 22.11.5 Kerberos Authorization Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 871 22.11.6 Kerberos Version 5 enhancements. . . . . . . . . . . . . . . . . . . . . . . 871
22.12 Remote access authentication protocols. . . . . . . . . . . . . . . . . . . . . . . 872 22.13 Extensible Authentication Protocol (EAP) . . . . . . . . . . . . . . . . . . . . . . 874 22.14 Layer 2 Tunneling Protocol (L2TP) . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
22.14.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876 22.14.2 Protocol overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877 22.14.3 L2TP security issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
22.15 Secure Electronic Transaction (SET) . . . . . . . . . . . . . . . . . . . . . . . . . 880 22.15.1 SET roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880 22.15.2 SET transactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 881 22.15.3 The SET certificate scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883
22.16 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
Chapter 23. Port based network access control . . . . . . . . . . . . . . . . . . . 889 23.1 Port based network access control (NAC) overview . . . . . . . . . . . . . . . 890 23.2 Port based NAC component overview . . . . . . . . . . . . . . . . . . . . . . . . . 891 23.3 Port based network access control operation . . . . . . . . . . . . . . . . . . . . 892
23.3.1 Port based network access control functional considerations. . . . 904 23.4 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906
Chapter 24. Availability, scalability, and load balancing . . . . . . . . . . . . . 907 24.1 Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909 24.2 Scalability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909 24.3 Load balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910 24.4 Clustering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910 24.5 Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912 24.6 Virtual Router Redundancy Protocol (VRRP) . . . . . . . . . . . . . . . . . . . . 914
Contents xv
24.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914 24.6.2 VRRP definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916 24.6.3 VRRP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916 24.6.4 Sample configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918 24.6.5 VRRP packet format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
24.7 Round-robin DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921 24.8 Alternative solutions to load balancing . . . . . . . . . . . . . . . . . . . . . . . . . 921
24.8.1 Network Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922 24.8.2 Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923
Appendix A. Multiprotocol Label Switching . . . . . . . . . . . . . . . . . . . . . . . 925 A.1 MPLS: An introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926
A.1.1 Conventional routing versus MPLS forwarding mode. . . . . . . . . . . 926 A.1.2 Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927 A.1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 929
A.2 MPLS network processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932 A.2.1 Label swapping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932 A.2.2 Label switched path (LSP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934 A.2.3 Label stack and label hierarchies . . . . . . . . . . . . . . . . . . . . . . . . . . 934 A.2.4 MPLS stacks in a BGP environment. . . . . . . . . . . . . . . . . . . . . . . . 936 A.2.5 Label distribution protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 938 A.2.6 Stream merge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 939
A.3 Emulating Ethernet over MPLS networks . . . . . . . . . . . . . . . . . . . . . . . . 939 A.4 Generalized Multiprotocol Label Switching (GMPLS) . . . . . . . . . . . . . . . 941
A.4.1 Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941 A.4.2 MPLS and GMPLS comparison in OTN environment. . . . . . . . . . . 942 A.4.3 How does GMPLS work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943 A.4.4 Link Management Protocol (LMP) . . . . . . . . . . . . . . . . . . . . . . . . . 944 A.4.5 Signaling for route selection and path setup. . . . . . . . . . . . . . . . . . 947 A.4.6 GMPLS considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949 A.4.7 GMPLS examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950
A.5 RFCs relevant to this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
Abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
Related publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959 IBM Redbooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959 Other publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959 Online resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959 How to get IBM Redbooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961 Help from IBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
Notices
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© Copyright IBM Corp. 1989-2006. All rights reserved. xvii
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xviii TCP/IP Tutorial and Technical Overview
Preface
The TCP/IP protocol suite has become a staple of today's international society and global economy. Continually evolving standards provide a wide and flexible foundation on which an entire infrastructure of applications are built. Through these we can seek entertainment, conduct business, make financial transactions, deliver services, and much, much more.
However, because TCP/IP continues to develop and grow in order to meet the changing needs of our communities, it might sometimes be hard to keep track of new functionality or identify new possibilities. For this reason, the TCP/IP Tutorial and Technical Overview provides not only an introduction to the TCP/IP protocol suite, but also serves as a reference for advanced users seeking to keep their TCP/IP skills aligned with current standards. It is our hope that both the novice and the expert will find useful information in this publication.
In Part I, you will find an introduction to the core concepts and history upon which TCP/IP is founded. Included is an introduction to the history of TCP/IP and an overview of its current architecture. We also provide detailed discussions about the protocols that comprise the suite, and how those protocols are most commonly implemented.
Part II expands on the information provided in Part I, providing general application concepts (such as file sharing) and specific application protocols within those concepts (such as the File Transfer Protocol, or FTP). Additionally, Part II discusses applications that might not be included in the standard TCP/IP suite but, because of their wide use throughout the Internet community, are considered de facto standards.
Finally, Part III addresses new concepts and advanced implementations within the TCP/IP architecture. Of particular note, Part III examines the convergence of many formerly disparate networks and services using IP technology. Conjointly, this section reviews potential dangers of this IP convergence and approaches the ever-growing standards used to secure and control access to networks and networked resources.
We purposely kept this book platform independent. However, we recognize that you might have a need to learn more about TCP/IP on various platforms, so the following Web sites might assist you in further researching this topic:
TCP/IP and System z:
http://www.ibm.com/servers/eserver/support/xseries/allproducts/insta lling.html
The team that wrote this redbook This redbook was produced by a team of specialists from around the world working at the International Technical Support Organization, Poughkeepsie Center.
Lydia Parziale is a Project Leader for the ITSO team in Poughkeepsie, New York with domestic and international experience in technology management including software development, project leadership, and strategic planning. Her areas of expertise include e-business development and database management technologies. Lydia is a Certified IT Specialist with an MBA in Technology
Management and has been employed by IBM for 23 years in various technology areas.
David T. Britt is a Software Engineer for IBM in Research Triangle Park, NC, working specifically with the z/OS® Communications Server product. He is a subject matter expert in the Simple Networking Management Protocol (SNMP) and File Transfer Protocol (FTP), and has written educational material for both in the form of IBM Technotes, Techdocs, and Webcasts. He holds a degree in Mathematical Sciences from the University of North Carolina in Chapel Hill, and is currently pursuing a master of science in Information Technology and Management
from the University of North Carolina in Greensboro.
xx TCP/IP Tutorial and Technical Overview
Jason Forrester is an IT Architect for IBM Global Technology Services in Boulder, CO. He has more than 12 years of experience with network communications. Specializing in IT strategy and architecture, Jason has designed large-scale enterprise infrastructures. He holds a CCIE certification and his work has lead to multiple patents on advanced networking concepts.
Dr. Wei Liu received his Ph.D. from Georgia Institute of Technology. He has taught TCP/IP networks in the University of Maryland (UMBC campus) and he has participated in ICCCN conference organization committees. Dr. Liu has given lectures at Sun™ Yat-Sen University and Shantou University in Next Generation Networks (NGNs). With more than 30 technical publications (in packet networks, telecommunications, and standards), he has received several awards from ATIS
committees. Dr. Wei Liu has more than 10 years of telecom industry experience, having participated in various network transformation projects and service integration programs. Currently, he is investigating new infrastructure opportunities (virtualization, network, services, security, and metadata models) that can lead to future offering and new capabilities.
Preface xxi
Thanks to the following people for their contributions to this project and laying the foundation for this book by writing the earlier version:
Adolfo Rodriguez, John Gatrell, John Karas, Roland Peschke, Srinath Karanam, and Martín F. Maldonado International Technical Support Organization, Poughkeepsie Center
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Carolyn Matthews is an IT Architect for IBM Global Technology Services in South Africa. She is an infrastructure architect for one of South Africa’s largest accounts. She also acts as a consultant, using various IBM techniques. Carolyn holds an honors degree in Information Systems and is currently pursuing her master’s degree in Information Systems. Her areas of expertise include TCP/IP networks, IT architecture, and new technologies.
Nicolas Rosselot is a Developer from Santiago, Chile. He has most recently been teaching an “Advanced TCP/IP Networking” class at Andres Bello University.
xxii TCP/IP Tutorial and Technical Overview
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Preface xxiii
Part 1 Core TCP/IP protocols
The Transmission Control Protocol/Internet Protocol (TCP/IP) suite has become the industry-standard method of interconnecting hosts, networks, and the Internet. As such, it is seen as the engine behind the Internet and networks worldwide.
Although TCP/IP supports a host of applications, both standard and nonstandard, these applications could not exist without the foundation of a set of core protocols. Additionally, in order to understand the capability of TCP/IP applications, an understanding of these core protocols must be realized.
With this in mind, Part I begins with providing a background of TCP/IP, the current architecture, standards, and most recent trends. Next, the section explores the two aspects vital to the IP stack itself. This portion begins with a discussion of the network interfaces most commonly used to allow the protocol suite to interface with the physical network media. This is followed by the protocols that must be implemented in any stack, including protocols belonging to the IP and transport layers.
Part 1
© Copyright IBM Corp. 1989-2006. All rights reserved. 1
Finally, other standard protocols exist that might not necessarily be required in every implementation of the TCP/IP protocol suite. However, there are those that can be very useful given certain operational needs of the implementation. Such protocols include IP version 6, quality of service protocols, and wireless IP.
2 TCP/IP Tutorial and Technical Overview
Chapter 1. Architecture, history, standards, and trends
Today, the Internet and World Wide Web (WWW) are familiar terms to millions of people all over the world. Many people depend on applications enabled by the Internet, such as electronic mail and Web access. In addition, the increase in popularity of business applications places additional emphasis on the Internet. The Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite is the engine for the Internet and networks worldwide. Its simplicity and power has led to its becoming the single network protocol of choice in the world today. In this chapter, we give an overview of the TCP/IP protocol suite. We discuss how the Internet was formed, how it developed, and how it is likely to develop in the future.
1
1.1 TCP/IP architectural model
The TCP/IP protocol suite is so named for two of its most important protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP). A less used name for it is the Internet Protocol Suite, which is the phrase used in official Internet standards documents. In this book, we use the more common, shorter term, TCP/IP, to refer to the entire protocol suite.
1.1.1 Internetworking
The main design goal of TCP/IP was to build an interconnection of networks, referred to as an internetwork, or internet, that provided universal communication services over heterogeneous physical networks. The clear benefit of such an internetwork is the enabling of communication between hosts on different networks, perhaps separated by a large geographical area.
The words internetwork and internet are simply a contraction of the phrase interconnected network. However, when written with a capital “I”, the Internet refers to the worldwide set of interconnected networks. Therefore, the Internet is an internet, but the reverse does not apply. The Internet is sometimes called the connected Internet.
The Internet consists of the following groups of networks:
Backbones: Large networks that exist primarily to interconnect other networks. Also known as network access points (NAPs) or Internet Exchange Points (IXPs). Currently, the backbones consist of commercial entities.
Regional networks connecting, for example, universities and colleges.
Commercial networks providing access to the backbones to subscribers, and networks owned by commercial organizations for internal use that also have connections to the Internet.
Local networks, such as campus-wide university networks.
In most cases, networks are limited in size by the number of users that can belong to the network, by the maximum geographical distance that the network can span, or by the applicability of the network to certain environments. For example, an Ethernet network is inherently limited in terms of geographical size. Therefore, the ability to interconnect a large number of networks in some hierarchical and organized fashion enables the communication of any two hosts belonging to this internetwork.
Figure 1-1 shows two examples of internets. Each consists of two or more physical networks.
Figure 1-1 Internet examples: Two interconnected sets of networks, each seen as one logical network
Another important aspect of TCP/IP internetworking is the creation of a standardized abstraction of the communication mechanisms provided by each type of network. Each physical network has its own technology-dependent communication interface, in the form of a programming interface that provides basic communication functions (primitives). TCP/IP provides communication services that run between the programming interface of a physical network and user applications. It enables a common interface for these applications, independent of the underlying physical network. The architecture of the physical network is therefore hidden from the user and from the developer of the application. The application need only code to the standardized communication abstraction to be able to function under any type of physical network and operating platform.
As is evident in Figure 1-1, to be able to interconnect two networks, we need a computer that is attached to both networks and can forward data packets from one network to the other; such a machine is called a router. The term IP router is also used because the routing function is part of the Internet Protocol portion of the TCP/IP protocol suite (see 1.1.2, “The TCP/IP protocol layers” on page 6).
Two networks interconnected by a router equals Internet A
Router
R
Router
Router
R
Multiple networks interconnected by routers (also seen as 1 virtual network, an Internet)
Two networks interconnected by a router equals Internet A
Router
R
Router
Router
R
Multiple networks interconnected by routers (also seen as 1 virtual network, an Internet)
Chapter 1. Architecture, history, standards, and trends 5
To be able to identify a host within the internetwork, each host is assigned an address, called the IP address. When a host has multiple network adapters (interfaces), such as with a router, each interface has a unique IP address. The IP address consists of two parts:
IP address = <network number><host number>
The network number part of the IP address identifies the network within the internet and is assigned by a central authority and is unique throughout the internet. The authority for assigning the host number part of the IP address resides with the organization that controls the network identified by the network number. We describe the addressing scheme in detail in 3.1.1, “IP addressing” on page 68.
1.1.2 The TCP/IP protocol layers
Like most networking software, TCP/IP is modeled in layers. This layered representation leads to the term protocol stack, which refers to the stack of layers in the protocol suite. It can be used for positioning (but not for functionally comparing) the TCP/IP protocol suite against others, such as Systems Network Architecture (SNA) and the Open System Interconnection (OSI) model. Functional comparisons cannot easily be extracted from this, because there are basic differences in the layered models used by the different protocol suites.
By dividing the communication software into layers, the protocol stack allows for division of labor, ease of implementation and code testing, and the ability to develop alternative layer implementations. Layers communicate with those above and below via concise interfaces. In this regard, a layer provides a service for the layer directly above it and makes use of services provided by the layer directly below it. For example, the IP layer provides the ability to transfer data from one host to another without any guarantee to reliable delivery or duplicate suppression. Transport protocols such as TCP make use of this service to provide applications with reliable, in-order, data stream delivery.
Figure 1-2 shows how the TCP/IP protocols are modeled in four layers.
Figure 1-2 The TCP/IP protocol stack: Each layer represents a package of functions
These layers include:
Application layer The application layer is provided by the program that uses TCP/IP for communication. An application is a user process cooperating with another process usually on a different host (there is also a benefit to application communication within a single host). Examples of applications include Telnet and the File Transfer Protocol (FTP). The interface between the application and transport layers is defined by port numbers and sockets, which we describe in more detail in 4.1, “Ports and sockets” on page 144.
Transport layer The transport layer provides the end-to-end data transfer by delivering data from an application to its remote peer. Multiple applications can be supported simultaneously. The most-used transport layer protocol is the Transmission Control Protocol (TCP), which provides connection-oriented reliable data delivery, duplicate data suppression, congestion control, and flow control. We discuss this in more detail in 4.3, “Transmission Control Protocol (TCP)” on page 149.
Another transport layer protocol is the User Datagram Protocol (see 4.2, “User Datagram Protocol (UDP)” on page 146). It provides connectionless, unreliable,
Applications
Transport
Internetwork
best-effort service. As a result, applications using UDP as the transport protocol have to provide their own end-to-end integrity, flow control, and congestion control, if desired. Usually, UDP is used by applications that need a fast transport mechanism and can tolerate the loss of some data.
Internetwork layer The internetwork layer, also called the internet layer or the network layer, provides the “virtual network” image of an internet (this layer shields the higher levels from the physical network architecture below it). Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol that does not assume reliability from lower layers. IP does not provide reliability, flow control, or error recovery. These functions must be provided at a higher level.
IP provides a routing function that attempts to deliver transmitted messages to their destination. We discuss IP in detail in Chapter 3, “Internetworking protocols” on page 67. A message unit in an IP network is called an IP datagram. This is the basic unit of information transmitted across TCP/IP networks. Other internetwork-layer protocols are IP, ICMP, IGMP, ARP, and RARP.
Network interface layer The network interface layer, also called the link layer or the data-link layer, is the interface to the actual network hardware. This interface may or may not provide reliable delivery, and may be packet or stream oriented. In fact, TCP/IP does not specify any protocol here, but can use almost any network interface available, which illustrates the flexibility of the IP layer. Examples are IEEE 802.2, X.25 (which is reliable in itself), ATM, FDDI, and even SNA. We discuss some physical networks and interfaces in Chapter 2, “Network interfaces” on page 29.
TCP/IP specifications do not describe or standardize any network-layer protocols per se; they only standardize ways of accessing those protocols from the internetwork layer.
A more detailed layering model is included in Figure 1-3.
Figure 1-3 Detailed architectural model
1.1.3 TCP/IP applications
The highest-level protocols within the TCP/IP protocol stack are application protocols. They communicate with applications on other internet hosts and are the user-visible interface to the TCP/IP protocol suite.
All application protocols have some characteristics in common:
They can be user-written applications or applications standardized and shipped with the TCP/IP product. Indeed, the TCP/IP protocol suite includes application protocols such as:
– Telnet for interactive terminal access to remote internet hosts
– File Transfer Protocol (FTP) for high-speed disk-to-disk file transfers
– Simple Mail Transfer Protocol (SMTP) as an internet mailing system
These are some of the most widely implemented application protocols, but many others exist. Each particular TCP/IP implementation will include a lesser or greater set of application protocols.
They use either UDP or TCP as a transport mechanism. Remember that UDP is unreliable and offers no flow-control, so in this case, the application has to provide its own error recovery, flow control, and congestion control functionality. It is often easier to build applications on top of TCP because it is a reliable stream, connection-oriented, congestion-friendly, flow control-enabled protocol. As a result, most application protocols will use TCP, but there are applications built on UDP to achieve better performance through increased protocol efficiencies.
Most applications use the client/server model of interaction.
Applications
Transport
Internetwork
The client/server model TCP is a peer-to-peer, connection-oriented protocol. There are no master/subordinate relationships. The applications, however, typically use a client/server model for communications, as demonstrated in Figure 1-4.
A server is an application that offers a service to internet users. A client is a requester of a service. An application consists of both a server and a client part, which can run on the same or on different systems. Users usually invoke the client part of the application, which builds a request for a particular service and sends it to the server part of the application using TCP/IP as a transport vehicle.
The server is a program that receives a request, performs the required service, and sends back the results in a reply. A server can usually deal with multiple requests and multiple requesting clients at the same time.
Figure 1-4 The client/server model of applications
Most servers wait for requests at a well-known port so that their clients know to which port (and in turn, which application) they must direct their requests. The client typically uses an arbitrary port called an ephemeral port for its communication. Clients that want to communicate with a server that does not use a well-known port must have another mechanism for learning to which port they must address their requests. This mechanism might employ a registration service such as portmap, which does use a well-known port.
For detailed information about TCP/IP application protocols, refer to Part 2, “TCP/IP application protocols” on page 405.
Client A
Bridges, routers, and gateways There are many ways to provide access to other networks. In an internetwork, this done with routers. In this section, we distinguish between a router, a bridge, and a gateway for allowing remote network access:
Bridge Interconnects LAN segments at the network interface layer level and forwards frames between them. A bridge performs the function of a MAC relay, and is independent of any higher layer protocol (including the logical link protocol). It provides MAC layer protocol conversion, if required.
A bridge is said to be transparent to IP. That is, when an IP host sends an IP datagram to another host on a network connected by a bridge, it sends the datagram directly to the host and the datagram “crosses” the bridge without the sending IP host being aware of it.
Router Interconnects networks at the internetwork layer level and routes packets between them. The router must understand the addressing structure associated with the networking protocols it supports and take decisions on whether, or how, to forward packets. Routers are able to select the best transmission paths and optimal packet sizes. The basic routing function is implemented in the IP layer of the TCP/IP protocol stack, so any host or workstation running TCP/IP over more than one interface could, in theory and also with most of today's TCP/IP implementations, forward IP datagrams. However, dedicated routers provide much more sophisticated routing than the minimum functions implemented by IP.
Because IP provides this basic routing function, the term “IP router,” is often used. Other, older terms for router are “IP gateway,” “Internet gateway,” and “gateway.” The term gateway is now normally used for connections at a higher layer than the internetwork layer.
A router is said to be visible to IP. That is, when a host sends an IP datagram to another host on a network connected by a router, it sends the datagram to the router so that it can forward it to the target host.
Gateway Interconnects networks at higher layers than bridges and routers. A gateway usually supports address mapping fro

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