Introduction to Network Programming in UNIX & LINUX

Introduction to Network Programming in UNIX & LINUX
© Daniel Zinchin Tel-Ran Ltd

And what could we learn from the INTERNET ?
Instead of Preamble… בס"ד Rabbi Avraham Yaakov 100 years ago taught his Chassids: - It is possible to learn from anything. Everything in this world exists to edify us. Not only what the Lord has made, but also what people have made, makes us wise. - What, for example, do we learn from a railway? - one Chassid asked in doubt - That, having been late for an instant, it is possible to miss entirely. - And telegraph? - That each word is taken into account. - And phone? - That everything told by you here, is audible there. And what could we learn from the INTERNET ? Introduction to Network Programming in UNIX & LINUX

Course Contents Network Primes Inter-Process Communication (IPC)
Thread Host Independent Network INTERNET Network Primes Inter-Process Communication (IPC) Inter-Host Communication (IHC) Multi-Threading and Synchronization Introduction to Network Programming in UNIX & LINUX

Recommended Literature and References:
W. Richard Stevens personal site: 1. W. Richard Stevens. UNIX Network Programming, Prentice Hall, 1990. 2. W. Richard Stevens. UNIX Network Programming, 2nd Edition, Prentice Hall, Vol.1 Networking APIs Vol.2 Interprocess Communications 3. W. Richard Stevens. TCP/IP Illustrated. Addison-Wesley, Vol.1 The Protocols Vol.2 The Implementation Vol.3 TCP for Transactions, HTTP, NNTP, and the UNIX Domain Protocols With gratitude to my Tel-Ran teacher Kolman Shkolnik, whose book was used during the preparation of materials for this course. 4. Douglas E. Cormer. Internetworking with TCP/IP Kolman Shkolnik. Introduction to Internetworking in UNIX. Tel-Ran 1995 Introduction to Network Programming in UNIX & LINUX

The History <1960 - Data transportation in the form of bits
Transportation of data packets Bell Labs, General Electrics and MIT develop Multix (Multiplexed Information and Computing Service) Ken Thompson and Dennis Ritchie in AT&T begin to develop UNICS (UNiplexed Information and Computing Service) First releases of UNIX in AT&T First UNIX network application UUCP (UNIX-to-UNIX copy program) . File transfer and electronic mail. AT&T Version 7 UNIX (1978) Berkley Version 7 UNIX (Eric Schmidt, Berkley University) File transfer, , remote printing DARPA (Defense Advanced Research Projects Agency) ARPANET, TCP/IP protocols development for Berkley Unix BSD UNIX system (Berkley Software Distribution) with Socket Interface Richard Stallman announces the GNU Project, an attempt to create a free operating system AT&T System V UNIX with Transport Layer Interface (TLI) File transfer, , remote printing, remote command execution. NSFNET (National Science Foundation) – remote access to super-computer network. BSD UNIX. Available source code of DARPA TCP/IP, Xerox NS protocols. End 80s - Microsoft Xenix, System V for Intel 8086, 80286, processors IEEE (Institute of Electrical & Electronical Engineers) defines POSIX – standard operation system interface. Unix System V Release 4.0 (SVR4). Merge of AT&T System V with SunOS (4.xBSD derivative) Provides ANSI compliant C compiler. Linus Torvalds (Finland) introduces Linux – freeware OS for PC. Sun introduces Solaris based on SVR4. Red Hat Linux released. Sun releases Solaris 8 having big success > Multiple releases and popularity growth of Linux derivatives Introduction to Network Programming in UNIX & LINUX

Basic Terms Computer Network
Communication system for connecting end-systems. Enables to share data, programs and resources (distributed systems). There are physical networks and logical networks. Host Single computer, end-system. Could be personal computer, dedicated system (print or file server) or time-sharing system. Process Any program which is executed by computer’s operation system. Thread Separate part of process, providing it’s specific working flow, and sharing the process data and resources with other threads. Inter-Process Communication Sharing of information and resources by two or more different processes. Inter-Host Communication Communication between two or more processes, running on different hosts in the network. Communication Protocol Set of rules and conventions that communication participants must follow. Introduction to Network Programming in UNIX & LINUX

Set of interconnected independent computer networks.
What is Internet Internet Set of interconnected independent computer networks. Uses common suite of protocols called TCP/IP. Managed by groups of representatives: IAB -Internet Activity Board NIC -National Information Center FNC -Federal Network Center Internet Services Transport Level: Unreliable packet delivery Reliable stream transport Application Level: File Transfer (FTP, TFTP) Electronic Mail (SMTP) Remote Login (TELNET) Network File System (NFS) Remote Program Execution Shared peripheral devices RFC - Request For Comments The name of the result and the process for creating a standard on the Internet. The proposals are reviewed by the Internet Engineering Task Force. New standards are proposed and published on the Internet, as a Request For Comments with acronym RFC <#>. Introduction to Network Programming in UNIX & LINUX

Layering and Protocol Family
Example of Layering in Communication System. Transfer of Knowledge by Means of Inter-Person Verbal Communication Layering is decomposition of task into subsystems (pieces), designed as sequence of horizontal layers. As result, each layer: concentrate on providing a particular function is built in terms of one layer below provides means to building various types of upper neighbor layer. Protocol Family (Suite) is set of interfaces between layers or inside layer. Peer-to-Peer Protocol is the protocol used between two entities of the same layer. Knowledge Concepts Speech Voice Transmitter Knowledge Concepts Speech Voice Receiver Sound Waves Introduction to Network Programming in UNIX & LINUX

7-Layer OSI Model 7 6 5 4 3 2 1 OSI Model
Open System Interconnection Model ISO International Standard Organization The 7-Layer OSI Model, developed by ISO (1984), is the guide, providing a detailed standard for describing of a network . Advantage of layering is to provide well-defined interfaces between the layers, when change in one layer doesn’t affect an adjacent layer. 7 6 5 4 3 2 1 Application Presentation Session Transport Network Data Link Physical bits frames packets datagrams messages (kinds of compression) (dialog management) (inter-process level) (inter-host level) (network topology) Introduction to Network Programming in UNIX & LINUX

4-Layer Simplified Model of TCP/IP
TCP/IP Protocol Suite actually was developed ( ) before formulation of 7-layer ISO OSI Model (1984). It implements 4-layer Simplified Communication Model: (inter-host level) Physical Data Link Network Transport Session Presentation Application 7 6 5 4 3 2 1 (inter-process level) (dialog management) (kinds of compression) bits frames packets datagrams messages (network topology) (communication end-point) (network topology & physical connection) Introduction to Network Programming in UNIX & LINUX

Protocol Suite For 4-Layer TCP/IP Model
application layer protocols Application Transport Network Data Link Application Transport Network Data Link messages transport layer protocols datagrams network layer protocols packets data link protocols frames physical connection bits Protocol Suite for 4-Layer TCP/IP Model contains 4 types of peer-to-peer protocols: Application Layer protocols – end-point communication Transport Layer protocols – inter-process communication Network layer protocols – inter-host communication Data Link protocols – topology-specific interface with physical network Introduction to Network Programming in UNIX & LINUX

TCP/IP Model and Protocol Suite
TFTF Trivial File Transfer Protocol UDP User Datagram Protocol TCP Transmission Control Protocol IP Internet Protocol ICMP Internet Control Message Protocol ARP Address Resolution Protocol RARP Reverse Address Resolution Protocol Ethernet A local area network architecture with broadcast bus topology Token Ring A local area network architecture with ring topology and token passing scheme Provided by kernel of OS UNIX Application 1 user application Application 0 Transport Network Data Link TFTP UDP TCP IP ARP ICMP RARP Ethernet Token Ring messages/stream datagrams IP Address + Port packets frames Physical Address bits physical connection Introduction to Network Programming in UNIX & LINUX

Network LAN MAN WAN Network Type Technology Speed LAN Coaxial cable,
fiber optics, Wi-Fi (wireless technology) 4 Mbit/s – 2 Gbit/s MAN microwave link 56 Kbit/s – 155 Mbit/s WAN Telephone lines, microwave link, satellite channels 9.6 Kbit/s – 45 Mbit/s LAN Local Area Network is a computer network comprises a local area, like a home, office, or group of buildings. MAN Metropolitan Area Network is large computer network usually spanning a city. WAN Wide Area Network is a computer network covering a broad geographical area. Largest and most well-known example of a WAN is the Internet. Gateway is a system, that interconnects two or more networks Introduction to Network Programming in UNIX & LINUX

Communication Activities
Data Transmission Communication Networks can be divided into two basic types by method of data transmission: circuit-switched and packet-switched. Encapsulation Encapsulation is hiding of object data from rest of the world. For protocol suite this means adding of control information to data when going one layer down. Multiplexing and Demultiplexing Multiplexing means “to combine many into one”. For network this means combining of data accepted from different functionalities of neighbor layer. Demultiplexing is reverse of multiplexing. Routing Routing is making decision, what route the packet should take. Static Routing is based on precomputed information. Dynamic Routing is depends on state of network configuration in the specific moment of time. Fragmentation and Reassembling Fragmentation (or segmentation) is breaking up of a packet into smaller pieces (MTU – maximal transmission unit) Reassembling is reverse of fragmentation, it is restoring of original packet from smaller pieces used for transmission. Introduction to Network Programming in UNIX & LINUX

Data Transmission Method
Communication Networks can be divided into two basic types by method of data transmission: circuit-switched and packet-switched. Circuit-Switched Data Transmission circuit Non-shared dedicated communication line is established Information transmitted without division Connection established once, then all data transmitted through this connection. Packet-Switched Data Transmission hop Shared communication links are used instead of dedicated line Information is divided into pieces – packets. Each packet contains the address of destination and separately routed over shared data links. The TCP/IP Internet uses packet-switched data transmission, provided by IP (Network) layer, responsible for forwarding of IP packets. Introduction to Network Programming in UNIX & LINUX

Data Encapsulation in TCP/IP
Encapsulation is hiding of object data from rest of the world. For protocol suite this means adding of control information to data when going one layer down. Example. Data encapsulation during mail delivery interesting very letter Data Application data TFTP header Data TFTP message UDP header TFTP header Data UDP datagram address address address IP header UDP header TFTP header Data IP packet Ethernet header IP header UDP header TFTP header Data Ethernet trailer Ethernet frame Bytes: Introduction to Network Programming in UNIX & LINUX

Multiplexing and Demultiplexing in TCP/IP. Example.
Multiplexing means “to combine many into one”. For network this means combining of data accepted from different functionalities of neighbor layer. Demultiplexing is reverse of multiplexing. Process 1 Process 2 Process 3 Process 4 UDP TCP IP Multi-homed Multi-user Host Ethernet interface Ethernet cable 1 Ethernet cable 2 TCP/IP Suite XNS Suite Process 5 Multiplexing Demultiplexing Introduction to Network Programming in UNIX & LINUX

Routing Data Link IP TCP Application Data Link IP TCP Application
Router is “intelligent” gateway, making a decision, what route (path) the packet should take. Data Link IP TCP Application Data Link IP TCP Application Remote packet is sent to Router Local packet is sent to Recipient hop 1 hop 2 hop 3 Data Link IP (router) Data Link IP (router) LAN1 LAN2 LAN3 Host 1 Gateway 1 Gateway 2 Host 2 In TCP/IP routing is made on IP Layer. Each packet could have its own route. The TCP/IP Internet uses Distributed Dynamic Routing. Distributed Dynamic Routing uses a mixture of global and local information to make routing decision. Introduction to Network Programming in UNIX & LINUX

Fragmentation and Reassembling
is breaking up of a packet into smaller pieces (transmission units). Maximal Transmission Unit (MTU) is maximal packet size held by network layer, depending on Data Link characteristics Reassembling is reverse of fragmentation. MTU=128 b MTU=2 Kb MTU=2 Kb Packet 1 Kb Data Link IP (router) fragmentation Data Link IP (router) reassembling Packet 1 Kb 128b 128b 128b . . . 128b 128b 128b LAN 1 WAN connection LAN 2 Gateway 1 Gateway 2 In TCP/IP fragmentation and reassembling is done at IP layer. The IP layer performs these activities depending on requirement of specific Data Link layers, hiding the technological differences between the networks. Introduction to Network Programming in UNIX & LINUX

Client-Server Model Client Server Service Protocol
requests provides Protocol uses is described by Client-Server Model is standard model for network applications. Typical Client scenario: Starts and connects to network Sends service request to known server Accepts the service Typical Server scenario: Starts and connects to network Waits for request from potential clients Accepts requests and provides service Waits for the next potential client… Introduction to Network Programming in UNIX & LINUX

Modes of Communication Service
Communication Service provided between two peer entities at any layer of the OSI Model. Connection Mode Connectionless Service Provides hop-by-hop transmission of separate messages. Each message transmitted independently and contains all the information (address) required for delivery. Datagram delivery service hop-by-hop Virtual circuit service end-to-end Connection-Oriented Service Provides establishment of dedicated end-to-end virtual circuit for data transmission. Connection-oriented data exchange involves three following steps: Connection establishment (performed once, requires overhead activity) Data transfer (can be lengthy) Connection termination The dedicated circuit is called virtual, because it could be provided even on network with packet-switched data transmission. A connection-oriented service is often used when more than one message is to be exchanged between the two peer entities. Introduction to Network Programming in UNIX & LINUX

Modes of Communication Service (continuation)
Data Stream Format Modes of Communication Service (continuation) Message Service Provides record boundaries . Byte Stream Does not provide record boundaries. Full-duplex - connection allows data to be transferred in both directions in the same time. Half-duplex - connection allows data to be transferred in both direction, but only one side to transfer at a time Simplex connection allows data to be transferred only in one direction (one end can only transmit and the other end can only receive.) Reliability Service is Reliable if it provides Sequencing and Error Control. Most of reliable services provide also Flow Control. Sequencing Means that the data is received by the receiver in the same order as it is transmitted by the sender. In a packet-switched network, it is possible for two consecutive packets to take different routes, and thus arrive at their destination in a different order from the order in which they were sent. Error Control Guarantees that error-free data is received at the destination. There are two conditions that can generate errors: - the data gets corrupted (modified during transmission), - the data gets lost. The network implementation has to provide for recovery from both these situations. Flow control (pacing) Assures that the sender does not send data at a rate faster than the receiver can process the data. If Flow Control is not provided, it is possible for the receiver to lose data because of lack of resources. Introduction to Network Programming in UNIX & LINUX

Summary: Communication Activities and Service Modes
combine/split of data from different Network (north) protocols hide Network layer data frame transmission in LAN Ethernet/ Token Ring Data Link unreliable packet delivery connection-less brake up (/recompose) packet into (/from) transition units distributed dynamic routing combine/split of data from different Transport (north) and Data Link (south) protocols hide Transport layer data Packet -switched (hop-by-hop) IP Network datagram delivery UDP reliable (sequencing, error control, flow control) full-duplex (bi-directional) byte stream connection-oriented brake up (/recompose) stream into (from) IP packets combine/split of data from different Application (north) processes hide Application layer data TCP Transport (application-depended) (application- depended) combine/split of data from different Transport (south) protocols application protocols Application Reliability Data Stream Format Connection Mode Fragmentation/ Reassembling Routing Multiplexing/ Demultiplexing Encapsulation Data Transmission Protocol Model Layer Communication Service Modes Communication Activities Introduction to Network Programming in UNIX & LINUX

Communication Services Provided by TCP/IP Protocol Suite
Network Layer IP – Internet Protocol Provides unreliable connectionless packet delivery service, containing: Routing, Fragmentation / Reassembling, Multiplexing / Demultiplexing. Works with different Data Link protocols and topologies, hiding the technological differences between the networks. Transport Layer UDP – User Datagram Protocol Provides unreliable connectionless datagram delivery service. TCP – Transmission Control Protocol Provides reliable connection-oriented full-duplex byte stream service over unreliable connectionless packet-switched IP Network. Introduction to Network Programming in UNIX & LINUX

Data Link Connection and Topology.
Transceiver This is communication device capable of transmitting and receiving of signals. Performs analog - digital - analog translation. Host Interface It provides physical address associated with interface hardware and filters incoming packets Transceiver Host Host Interface Coaxial cable (ether) Bus Topology The main characteristic of this topology is that it is a passive structure: when a node is down, the network is not affected. Ring Topology This kind of topology is less efficient and reliable but it is quite cheap. As soon as two lines are cut the network no longer works. Star Topology This topology is quite efficient and cheap. Most small local networks is built on this model by using a central Hub that connects computers together A hub can imitate different network topology configurations. Introduction to Network Programming in UNIX & LINUX

Data Link Equipment A B C Repeater A to B A to C All frames are transmitted to both segments A B C Bridge A to B A to C Local frames are filtered out Repeater is a hardware component that transmits frames from one wire and places them on another. Repeaters are a simple way to extend a LAN segment. Bridge is a hardware component that filters frames according to destination address. Bridges are used to connect multiple segments. Ring Imitation I O Hub I O Hub Buss Imitation Hub is a common connection point for devices in a network. Hub can imitate a bus or a ring or could be more sophisticated. In this case it called Switch. Introduction to Network Programming in UNIX & LINUX

Data Link Protocols: Ethernet
Ethernet is broadcast bus technology with best effort delivery. Was developed in the beginning of 70-s by Xerox corporation. Following development and standardizing was performed by DIX (Digital, Intel, Xerox) in In 1983 it was approved as standard by IEEE . Currently Fast Ethernet is one of most popular LAN technologies. IEEE (Institute of Electrical and Electronics Engineers) - professional world-wide society for electronics and electrical engineers) Technology description: Each host interface has preset unique 48 bit physical address. Transceiver senses when ether is in use and detects collisions. When data is transmitted, all hosts connected to the bus can hear the transmission. In case of collision both hosts wait for a random amount of time, before sending the information again. Collision occurs when two devices on a network try to transmit information at the same time. P – Preamble for synchronizing. The last byte is SFD – Start of Frame Delimiter DA – Destination Address SA – Source Address L/T – (Length/Type) Length of Data and optional ID of upper level protocol CRC – Cyclic Redundancy Check sum Ethernet Frame P DA SA L/T Data CRC Bytes: Introduction to Network Programming in UNIX & LINUX

Ethernet CSMA/CD algorithm
Begin Frame Sending 1. Prepare Frame 2. Trial Counter = 0 CSMA/CD Carrier Sense Multiple Access with Collision Detection IPG Inter-Packet Gap JAM 32 bit frame for collision signaling Wait Random Delay Time Is other node transmitting ? YES Is other node transmission finished ? NO NO Calculate Random Delay Time YES Delay NO Is IPG interval Passed ? NO YES Is Trial Counter Greater then 16 ? YES Wait until IPG is passed Trial Counter ++ Send the 1-st bit of Frame Waiting Send the 32-bit JAM YES Is Collision detected ? Send the Next bit of Frame Recovery After Collision NO Is Last bit sent ? NO YES Transmission Frame Sending Failure. Too many collisions. Frame is Sent Successfully Introduction to Network Programming in UNIX & LINUX

Data Link Protocols: Token Ring
Token Ring is deterministic technology with predictable delay. Was developed in 1980 – 1985 by IBM. Approved as standard by IEEE. Technology description: This is not continuous wire, consists of connections among host interfaces, connecting to Ring by means of Multiple Access Units (MAU). (No more than 8 hosts per MAU). Physical address is configurable by means of switches. Control frame named “Token” is passed from one host to another, allowing to this host (and only this) to send the packet. To send the frame, host performs the following steps: waits for the arriving Token converts it to data frame and copies to the next host in the Ring waits for the frame to return after delivery deletes the frame and sends out a new Token Each moment of time no more than 1 host sends the data, all other hosts copy the data by chain. Host interface could be in following modes: transmit mode – sending host copying mode – all other hosts in ring recovery mode – recovery in case of token loss When copying host recognizes its destination address, it cleans refuse bit. Sender, accepting the original frame, detects if frame was delivered, checking the refuse bit. Fist connected to Ring host accepts the status of Active Monitor. It responsible for: Token creation and recovery Check frame delivery timeout Deletion of frames not deleted by other hosts. Notification of other hosts about its presence in Ring (sends “Active Monitor Present” frame) In case of Active Monitor problem, other hosts compete to accept its status. Multiple Access Unit In Token Ring collisions never occur. This ensures good performance of network under big loads (30%-40%) Introduction to Network Programming in UNIX & LINUX

Token Ring (continuation)
Token Ring Data Frame Token Ring “Token” SD AC FC DA SA Data CRC ED FS SD AC ED Bytes: SD - Start Delimiter AC - Access Control - packet priority, type (token/data), active monitor bit FC - Frame Control DA - Destination Address SA - Source Address CRC - Cyclic Redundancy Check sum ED - End Delimiter - contains 1 bit – Last Packet bit, Error flag bit FS Frame Status - contains Parity bit (copy indicator), Refuse bit (destination reached) ETR – Early Token Release technology After sending of frame, the same host generates new Token. As result, many sequential frames could circulate in the Ring in the same time. But no more than one Token could present in each moment of time. This technology improves the performance of Token Ring. Introduction to Network Programming in UNIX & LINUX

Network Layer: Internet Protocol
Internet Protocol (IP) Provides unreliable connectionless packet delivery service, containing: Routing, Fragmentation / Reassembling, Multiplexing / Demultiplexing. Works with different Data Link layers, hiding the technological differences between the networks. Data Link Network Transport Application Ethernet IP (host) TCP/UDP application TokenRing IP (host) TCP/UDP application IP (router) IP (router) IP address hop 1 hop 2 hop 3 Ether net Ether net Ether net Token Ring Physical address LAN LAN LAN Introduction to Network Programming in UNIX & LINUX

Internet Protocol: IP(v4) Packet Structure
bits: 1-st byte 5-th byte 9-th byte 13-th byte 17-th byte Version – IP Version Header length – IP Header total length in 32bit words (max = 15*4=60 bytes) DSCP, ECN – type of service fields, used by upper protocols Total Length – total packet length (header + data). Identification, DF (don't fragment), MF (more fragments), Fragment Offset – used for fragmentation and reassembly. TTL - time-to-live – maximal number of hops, set by the sender, decremented by each router. Protocol - upper layer protocol (1=ICMP, 2=IGMP, 6=TCP, 17=UDP). Header Checksum - calculated over just the IP header including any options. Source IP address (32 bit) Destination IP address (32-bit) Options (<=40 bytes) , used by upper protocols Introduction to Network Programming in UNIX & LINUX

Internet Address Formats
Internet Address (IP address) is mandatory unique logical address which must have every host in Internet. IP Address (IPv4) is 32-bit number. Decimal Dotted Notation is human-oriented representation of IP Address as sequence of 4 decimal numbers separated by dot. The IP Address has internal structure. There are 5 classes of IP Address: Class A Host ID Network ID Bits: Class B 1 Bits: Class C Bits: Class D Multicast address Bits: Class E (reserved experimental format) Bits: * * *Note: The 2 types of bit sequences: All Bits equal 1 All Bits equal 0 are not used as Network IDs and Host IDs Class Range A to B to C to D to E to Networks Per Class 2^7 – 2 = 126 2^14 – 2 = 16,382 2^21 – 2 = 2,097,150 N/A Hosts Per Network 2^24 – 2 = 16,777,214 2^16 – 2 = 65,534 2^8 – 2 = 254 Introduction to Network Programming in UNIX & LINUX

Netmask Example. Host ID Network ID
Gateways, to locate the network, need only Network ID part of IP Address and don’t need to know the location of every host. This is important concept of routing. To calculate Network ID from IP Address, Gateways use Netmask. Class A B C Network ID 1 byte 2 bytes 3 bytes Netmask NETWORK_ID = IP_ADDRESS & NETMASK Example. Calculation of Network ID for IP Address = (Class B) 1 3 F 6 B 9 243 99. 11. 145. Host ID Network ID class B 0x 0. 255. IP Address Netmask of Class B Introduction to Network Programming in UNIX & LINUX

Network ID and Subnet ID
IP Addresses are assigned by specific authority: InterNIC- Internet Network Information Center. The InterNIC assigns only Network IDs. The assignment of Host IDs is responsibility of local site system administrator. IP addresses are often subnetted. Subnet adds additional level to the address hierarchy: Network ID (assigned to site) Subnet ID (chosen by site) Host ID (chosen by site) All the hosts on a given subnet share a common Subnet Mask, and this mask specifies the boundary between the subnet ID and the host ID. Bits of 1 in the subnet mask cover the network ID and subnet ID, and bits of 0 cover the host ID. SUBNETWORK_ADDR = IP_ADDRESS & SUBNET_MASK Example. Subnetting of Network with Class B address, using 8 bit Subnet ID. Subnet ID Class B Host ID Network ID 1 Bits: Bits: Network mask: Subnet mask: =0xFFFF0000 =0xFFFFFF00 In the example above local gateway needs only 8 bits of Subnet ID for routing. Adding new host to existing sub-network will not require any changes to the internal gateways. Introduction to Network Programming in UNIX & LINUX

Types of Destination IP Address
There are three Destination Types of IP addresses: Unicast (destined for a single host) Broadcast (destined for all hosts on a given network) Limited Broadcast to all hosts inside local network (Network ID = all 1, Host ID = all 1) Net-Directed Broadcast to all hosts of other local network (Network ID = netID, Host ID = all 1) Subnet-Directed Broadcast to all hosts in specific sub-network (Network ID = netID, Subnet ID = subnetId, Host ID = all 1) Multicast (destined for a set of hosts that belong to a multicast group or sub-network). Multicast Address is a special type of address that is recognizable by multiple hosts joined a Multicast Group . A Multicast Address is sometimes known as a Functional Address or a Group Address. Hosts that are interested in receiving data flowing to a particular group must join the group using: IGMP - Internet Group Management Protocol . multicast group Broadcasting and Multicasting needs support by hardware (Data Link layer). Broadcast and Multicast addresses could not be used as Source IP Address Introduction to Network Programming in UNIX & LINUX

Special Case IP Addresses
Loopback Addresses By convention, the address is assigned to the Loopback Interface. Anything sent to this IP address loops around and becomes IP input without ever leaving the machine. This address id often used when testing a client and server on the same host. Any address on the network 127/8 can be assigned to the loopback interface, but is and is often configured automatically by the IP stack. (This address is known as INADDR_LOOPBACK ) Unspecified Address The address consisting of 32 zero bits is Unspecified Address. It is only permitted to appear as the source address in packets sent by a node that is bootstrapping before the node learns its IP address. (This address is known as INADDR_ANY). Private Addresses Three address ranges are set aside for “Private Internets“. These are the networks that do not connect directly to the public Internet. Small sites use these private addresses and Network Address Translation (NAT) to a single public IP address visible to the Internet. NAT - Network Address Translation Also known as Network Masquerading or IP-masquerading is a technique in which the source and/or destination addresses of IP packets are rewritten as they pass through a router or firewall. It is most commonly used to enable multiple hosts on a private network to access the Internet using a single public IP address. Class Range Number of addresses A to 16,777,216 B to 1,048,576 C to 65,536 Introduction to Network Programming in UNIX & LINUX

Multihoming and Address Aliases
Multihomed Host This is a host with multiple interfaces. Each interface must have a unique IP address. (Loopback interface is not counted) A router, by definition, is multihomed since it forwards packets from one interface to another one. But, a multihomed host is not a router unless it forwards packets. There are two types of Multihoming: Physical Multihoming Host has multiple physical interfaces, each interface has its own IP address. Logical Multihoming Newer hosts have the capability to assigning multiple IP addresses to the same physical interface. Each additional IP address, after the first (primary), is called an Alias or Logical Interface. Multihomed Network This is a network that has multiple connections to the Internet. For example, some sites have two connections to the Internet instead of one, providing a backup capability. $ ifconfig -a eth0 Link encap:Ethernet HWaddr 00:11:25:0C:DE:88 inet addr: Bcast: Mask: inet6 addr: fe80::211:25ff:fe0c:de88/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets: errors:0 dropped:0 overruns:0 frame:0 TX packets: errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes: (304.3 MiB) TX bytes: (72.2 MiB) Base address:0x2000 Memory:e e lo Link encap:Local Loopback inet addr: Mask: inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU: Metric:1 RX packets: errors:0 dropped:0 overruns:0 frame:0 TX packets: errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes: (47.0 MiB) TX bytes: (47.0 MiB) ifconfig UNIX/LINUX utility for configuring network interface parameters Introduction to Network Programming in UNIX & LINUX

Domain Name System Domain Name System (DNS) nslookup
This is a distributed database that provides the mapping between IP addresses and hostnames. Hostnames are more suitable for human use, than IP addresses. The DNS is distributed because no single site on the Internet knows all the information. Each site maintains its own database of information and runs a DNS Server program that other systems across the Internet (clients) can query. The DNS provides the protocol that allows clients and servers to communicate with each other. Applications access the DNS through a Resolver. The resolver contacts one or more name servers to do the mapping. $nslookup gate88.mot.com Server: abcde.mot.com Address: Name: gate88.mot.com Address: nslookup UNIX utility for DNS information access The DNS Name Space is Hierarchical Tree. The InterNIC maintains the top-level domains: Generic Domains (com, edu, gov, int, mil, net, org) Country Domains (us, uk, il, ru, etc.) InterNIC delegates responsibility to others for specific Zones. A Zone is a subtree of the DNS tree that is administered separately. Many second-level domains then divide their zone into smaller zones. To accept the DNS information, every Name Server must know how to contact the Root Name Servers. The root server tells the requesting server to contact another server, and so on. A fundamental property of the DNS is Caching. Name Server caches accepted {IP Address ; Hostname} information for following reuse. Introduction to Network Programming in UNIX & LINUX

Address Resolution Data Link Ethernet Network IP Data Link Ethernet
Address Resolution is translation between Network Layer logical address and Data Link physical address. Host A Host B IP Address (logical) Ethernet Address (physical) Data Link Ethernet Network IP Data Link Ethernet Network IP IP packet IPA IPB Ethernet frame PHA PHB physical connection Address Resolution Problem I want to send IP packet to another host with known IP Address. What is Physical Address of that host? Known: IPA, PHA, IPB. Unknown: PHB Reverse Address Resolution Problem I’m diskless workstation. What is my own IP address ? Known: PHA. Unknown: IPA. Introduction to Network Programming in UNIX & LINUX

ARP X A Y B Z X A Y B Z ARP – Address Resolution Protocol
Solves Address Resolution Problem. Provides dynamic mapping from an IP Address to the corresponding Physical Address on the same physical network. ARP Request ( [ IPA , PHA] , [ IPB , ? ] ) ARP Request is Ethernet Broadcast frame (Destination Ph Address = 0xFFFFFFFFFFFF) is sent to all hosts in physical network. Only the host, recognizing its own IP Address in the Request, sends the ARP Reply, containing its Physical address. ARP Cache Maintains the recent mappings from Internet addresses to Physical addresses. Removes its entries after expiration time Proxy ARP Lets to Router to answer ARP requests, addressed to another physical network, substituting router’s physical address instead of target foreign host address. Than, accepting the frame, router forwards it to the target foreign host. X A Y B Z ARP Reply ( [ IPA , PHA] , [ IPB , PHB ] ) X A Y B Z arp UNIX utility for ARP Cache access $arp –a sun ( ) at 8:0:20:3:f6:42 svr4 ( ) at 0:0:c0:c2:9b:26 Introduction to Network Programming in UNIX & LINUX

RARP Protocols X A Y Z X A Y Z
RARP Request RARP – Reverse Address Resolution Protocol Solves Reverse Address Resolution Problem. Used by diskless hosts during its initialization (bootstrap). ( [ ? , PHA ] ) RARP Request is Ethernet Broadcast frame ,sent to all hosts in physical network. Only the RARP Server, containing the required information, sends RARP Reply, containing IP Address of requestor. RARP Server serves single LAN. It could be multiple RARP Servers in LAN. They handle Distributed Data Base of IP Addresses. RARP Servers provide delay mechanism to avoid simultaneous response to requestor from multiple RARP Servers in the same time. RARP Server X A Y Z RARP Reply ( [ IPA , PHA ] ) RARP Server X A Y Z BOOTP – Bootstrap Protocol Enables a diskless workstation to discover its own IP address, BOOTP Server IP address, and a file to be loaded into memory to boot the machine. Needs manual pre-configuration of the host information. Could be routed and serve more than one LAN. DHCP – Dynamic Host Configuration Protocol Allows dynamic allocation of network addresses and configurations to newly attached hosts. Allows recovery and reallocation of network addresses through a leasing mechanism. Does not require manual pre-configuration of the host information. Introduction to Network Programming in UNIX & LINUX

ICMP ICMP Data ICMP Header IP Header
ICMP - Internet Control Message Protocol. ICMP handles Error and Control information messages between routers and hosts. These messages are normally generated by and processed by the TCP/IP networking software. Example of usage: ping and traceroute programs use ICMP. ICMP Message ICMP Data ICMP Header IP Header CRC Code Type Type Description Query Error echo reply (ping reply) * 3 destination unreachable 4 quench (flow control) 5 redirect (use another router) 8 echo request (ping request) 9 router advertisement (reply to solicitation) 10 router solicitation (request for advertisement) 11 time exceeded (TTL=0) 12 parameter problem (bad IP header) 13 time stamp request (what time is it now) 14 timestamp reply (current time is…) 17 address mask request (give my subnet mask) 16 address mask reply (your subnet mask is …) Introduction to Network Programming in UNIX & LINUX

IP Routing IP Routing is distributed. Each hop of the specific packet is calculated separately. Ethernet IP (host) TCP/UDP application TokenRing IP (router) Ether net LAN hop 1 hop 2 hop 3 Token Ring Ether net Remote packet is sent to Router Local packet is sent to Recipient traceroute UNIX utility, printing the route which packets take to network host G hop1 hop2 hop3 istanbul% traceroute sanfrancisco traceroute to sanfrancisco ( ), 30 hops max, 40 byte packets 1 frbldg7c-86 ( ) ms ms ms 2 bldg1a-001 ( ) ms ms ms 3 bldg4-bldg1 ( ) ms ms ms 4 bldg6-bldg4 ( ) ms ms ms 5 ferbldg11a-001 ( ) ms ms ms 6 frbldg12b-153 ( ) ms ms ms 7 sanfrancisco ( ) ms ms ms Introduction to Network Programming in UNIX & LINUX

IP Routing: Routing Table
The IP layer has a Routing Table in memory that it searches each time it receives a datagram to send. The Routing Table contains the following information: Destination – IP Address of Destination Host (flag “H”) or Destination Network (no flag ”H”) Gateway – IP Address of Hop Router for Remote Network (flag “G”) or IP Address of Local Host in Directly Connected Network (no flag “G”) Flags – “U”- route is up, “G”- route to Remote Network via Gateway, “H” - route to specific Host, “D”- route was added because of an ICMP Redirect Message. Ref – The number of times the route used to establish a connection. Use – The number of transmitted packages Interface – The Network Interface used by route UNIX Utilities: route Utility for manual manipulation with Routing Table netstat Utility, showing network status interface Host Gateway Destination # netstat -nr Routing Table: IPv4 Destination Gateway Flags Ref Use Interface UH lo0 default UG U bge0 UG UG UG UGH Loopback Route (Local Host) via interface lo0 Default Router - Directly Connected Network via interface bge0 - Route to Remote Network via Gateway - Route to Remote Network via Gateway Route to Remote Network via Gateway Route to Remote Host via Gateway Introduction to Network Programming in UNIX & LINUX

IP Routing Algorithm Single IP Routing algorithm for Host an Router
Most multi-user systems today (almost every Unix system), can be configured to act as a Router. This means, that Host and Router could have the same routing algorithm. Note: Unlike Router, the Host never forwards packets from one of its interfaces to another. yes no Discard IP Packet. Send ICMP Error. Is Destination IP Address Found ? Extract Network ID Is Local Network ? Is Subnet Mask Specified ? Extract Sub-Network ID Is Sub-Network ID Found ? Is Network ID Found ? Is Default Route Found ? Is Directly Connected Network ? Get Gateway IP Address Find Directly Connected Network Get Interface Send IP Packet Make Routing Decision Introduction to Network Programming in UNIX & LINUX

Static and Dynamic IP Routing
Static Routing During Static Routing the Routing Table: created during interface configuration added by the route command or created by an ICMP redirect (if the wrong “default” was used) It is fine if the network is small, has a single connection point to other networks and does not have redundant routes (which could be used if a primary route fails) Dynamic Routing During Dynamic Routing the Routing Table also updated by Routing Daemon process. the Routing Daemon is running on the Router communicates with another Routers using a Routing Protocol dynamically updates the kernel's routing table with information it receives from neighbor routers Routing Protocols are separated to: IGP – Interior (Intra-Domain) Gateway Protocols Used between the Routers of one autonomous system. Examples: RIP – Routing Information Protocol , OSPF - Open Shortest Path First protocol. EGP – Exterior (Inter-Domain) Gateway Protocols Used between the Routers of different autonomous systems. Example: BGP – Border Gateway Protocol Introduction to Network Programming in UNIX & LINUX

(Destined to my IP Address
IP Routing Schema IP Input IP Output Routing Table write Routing Table read Routing Daemon route command netstat command Updates from adjacent Routers Manual updates by Sysadmin UDP TCP ICMP Redirect ICMP IGMP Deliver Message yes Is this My Packet ? (Destined to my IP Address or Broadcast Address) yes Is IP Forwarding Enabled ? no no no Routing Table IP output: Calculate Next Hop (to Destination Host or Hop Router) yes Process IP options. Is this Source Routing (prescribed by sender) ? Is Hop Calculated ? no yes Send IP Packet. Discard IP Packet. Send ICMP Error. Receive IP Packet. Put it to IP Input Queue IP Layer Physical Network Interfaces Introduction to Network Programming in UNIX & LINUX

Transport Layer: Port Numbers
Port Number is unique 16-bit identifier of Application Communication Endpoint, used by Transport Protocols. TCP ports and UDP ports are independent. Servers are normally known by their well-known port number. For example: FTP server always uses TCP port 21. Telnet server is on TCP port 23. TFTP server is on UDP port 69. Clients usually need any unique free port. Client port numbers are called ephemeral ports. Port number reservation: 1 – Well-Known Ports. Used by well-known servers across all Internet. 1024 – Registered Ports. Used by servers known across specific networks. – Dynamic Ports. Used as ephemeral port numbers. The ranges of Registered and Dynamic Ports are configurable. Application application Transport TCP/UDP Port number Network IP IP address Data Link Ethernet/ TokenRing Physical address Transport Protocols provide multiplexing / demultiplexing based on Port Number Port 1 Port 2 Port 3 #grep telnet /etc/services telnet 23/tcp #grep domain /etc/services domain 53/udp domain 53/tcp File /etc/services on most Unix systems the well-known port numbers are contained in this file. Transport Protocol (UDP/TCP) IP Introduction to Network Programming in UNIX & LINUX

Association and Transport Address
Communication link between two processes is completely specified by tuple Association: Transport Protocol (UDP / TCP) Local IP Address Local Port Foreign IP Address Foreign Port Transport Address (or Socket) is half-Association: Socket Pair defines the Association UDP Association Example Process A Process B application application UDP UDP Port A Port B IP IP IP Addr A IP Addr B data link data link Socket A = { UDP, Port A, IP Address A } Socket B = { UDP, Port B, IP Address B } Association = { UDP, Port A, IP Address A, Port B , IP Address B } Introduction to Network Programming in UNIX & LINUX

Transport Layer: UDP Protocol
UDP – User Datagram Protocol Provides unreliable connectionless datagram delivery service. UDP is a simple protocol: each output operation by a process produces exactly one UDP datagram, which causes one IP datagram to be sent. UDP Datagram Structure Source and Destination Port Numbers - identify the sending process and the receiving process. UDP length the length of the UDP header and the UDP data in bytes. (it is redundant, because could be calculated from IP header) UDP checksum covers the UDP Pseudo-Header (see below) and the UDP data. To let UDP double-check that the data has arrived at the correct destination, the UDP checksum is calculated on UDP Pseudo-Header, containing: UDP header itself IP Header fields: Source IP Address, Destination IP Address, Protocol type. DATA field may be empty Introduction to Network Programming in UNIX & LINUX

Transport Layer: TCP Protocol
TCP – Transmission Control Protocol Provides reliable connection-oriented full-duplex byte stream service over unreliable connectionless packet-switched IP Network TCP provides reliability by doing the following: The application data is broken into TCP Segments - the best sized chunks passed by TCP to IP. Each TCP Segment has its Sequence Number. When TCP receives data from the other end of the connection, it sends an Acknowledgment. When TCP sends a segment it maintains a Timer. If an acknowledgment isn't received in time, the segment is retransmitted. TCP maintains a Checksum on its header and data. If a segment arrives with an invalid checksum, TCP discards and doesn't acknowledge it, expecting the retransmission from sender after expiration of its timeout. TCP Re-Sequences the data if necessary, passing the received data in the correct order to the application. TCP provides discarding of duplicate data. TCP provides Flow Control. Each end of a TCP connection has a finite amount of buffer space. A receiving TCP allows the sender to send as much data as the receiver has buffers for. TCP Connection Establishing. Three – Way Handshake. Simple data exchange example. TCP Connection Termination. Modified Three – Way Handshake. SYN m SYN n, ACK m+1 ACK n+1 active side passive side data m FIN m ACK m+1 ACK m+1 data n-1 data m+1 ACK n data n, ACK m+2 FIN n ACK n+1 ACK n+1 Introduction to Network Programming in UNIX & LINUX

TCP Segment Structure Source and Destination port numbers - identify the sending process and the receiving process. Sequence Number – unique identifier of TCP Segment, equal to the sequence number of segment 1st data byte in stream between TCP sender and TCP receiver. Byte numeration begins from ISN (initial sequence number) chosen by TCP sender. Wraps back around to 0 after reaching 2^ Acknowledgement Number – used with ACK flag. The number of next byte, which TCP receiver is ready to receive. Header Length - the length of the header in 32-bit words. Flags: URG – urgent data (used with Urgent Pointer), ACK – acknowledge (used with Acknowledge Number) PSH - flush receiver data from its cache to process, RST – reset the connection (“port unreachable” reply) SYN – connect (used with Sequence Number = ISN), FIN – finalize the connection Window Size – number of bytes, which receiver is ready to accept (flow control) TCP Checksum - covers TCP Pseudo-Header (TCP Header + IP Addresses and Protocol fields) + TCP Data Urgent Pointer – used with URG flag. Offset from Sequence Number to last byte of urgent data. Options (<=40 bytes). Maximal Segment Size (MSS) announcement, Timestamp, Window scale, etc. Introduction to Network Programming in UNIX & LINUX

Can’t Sent, until window moves
TCP Sliding Window Sliding Window is algorithm of positive acknowledgement with re-transmission. Receive Buffer TCP Receiver Receive Window TCP Segments 1 2 3 4 … ACKed, accepted by application ACKed, NOT accepted by application Sliding direction Send Buffer TCP Sender Send Window TCP Segments 1 2 3 4 5 6 7 8 9 10 11 … Sent, ACKed Sent, NOT ACKed Can Sent immediately Can’t Sent, until window moves Receive Window – consists of any space in Receive Buffer that is not occupied by data. Data remains in Receive buffer until target application will accept it. The size of Receive Window is advertised by TCP Receiver to TCP Sender. Send Buffer begins from first un-acknowledged segment. Has the size of advertised Receive Window Size. Send Window covers unused part of the Send Buffer. Introduction to Network Programming in UNIX & LINUX

TCP State Transition Diagram
normal transition for Client normal transition for Server appl: state transition when application issues operation recv: state transition taken when segment received send: what is sent for this transaction The Legend: TIME_WAIT State The endpoint that initiates termination of connection, goes through TIME_WAIT state and remains there for the period: 2 * MSL (maximum segment lifetime) MSL is configurable life time of IP packet in the network. The actual duration of 2MSL varies from 30 sec up to 4 min. The TIME_WAIT state has two reasons: 1.Reliable termination of TCP connection (ability to reply ACK for resent FIN) 2.To allow old duplicate segments to expire in the network (1MSL for original duplicate segments + 1 MSL for replies to be lost from network) For the period of 2MSL the TCP prevents the incarnation (the restart from the same port) of the connection. Introduction to Network Programming in UNIX & LINUX

Modern protocols in TCP/IP Protocol Suite
IPv6 - Internet Protocol version 6. Network Layer protocol, designed in the mid-1990s as a replacement for IPv4. The major change is a larger address comprising 128 bits to deal with the explosive growth of the Internet in the 1990s. IPv6 addresses are 128 bits long and are usually written as eight 16-bit hexadecimal numbers. IPv6 provides packet delivery service for TCP, UDP, SCTP, and ICMPv6. ICMPv6 - Internet Control Message Protocol version 6. Is integral part of IPv6 implementation. ICMPv6 combines the functionality of ICMPv4, IGMP, and ARP. SCTP - Stream Control Transmission Protocol. Transport Layer protocol, providing Reliable Connection-Oriented Full-Duplex Message Service. Designed in SCTP connection called Association, because SCTP is Multihomed and involves a set of IP addresses and a single port for each side of an Association. SCTP provides a Message Service, which maintains record boundaries. As with TCP and UDP, SCTP can use either IPv4 or IPv6, but it can also use both IPv4 and IPv6 simultaneously on the same association. SCTP can provide multiple streams between connection endpoints, each with its own reliable sequenced delivery of messages. A lost message in one of these streams does not block delivery of messages in any of the other streams. Introduction to Network Programming in UNIX & LINUX

Virtual Network and Tunneling. The 6bone.
The 6bone is a virtual network that was created in 1996 for users with islands of IPv6-capable hosts wanted to connect them together using a virtual network without waiting for all the intermediate routers to become IPv6-capable. The 6bone is established on top of the existing IPv4 Internet using tunnels. Introduction to Network Programming in UNIX & LINUX

TCP/IP Summary IPv4 Internet Protocol version 4. IPv6
Transmission Control Protocol. UDP User Datagram Protocol. SCTP Stream Control Transmission Protocol. ICMP Internet Control Message Protocol (version 4). IGMP Internet Group Management Protocol. ARP Address Resolution Protocol. RARP Reverse Address Resolution Protocol. ICMPv6 Internet Control Message Protocol version 6. BPF BSD Packet Filter. Provides access to the datalink layer in Berkeley-derived kernels. DLPI Datalink Provider Interface. Provides access to the datalink layer in System V R4. IPv4 Applications IPv6 Applications dump tcp- routed m- ping route trace- appl. appl. appl. appl. appl. appl. route trace- ping ping API TCP SCTP UDP ICMP address 32-bit address 128-bit v6 ICMP v6 ICMP IGMP IPv4 IPv6 RARP ARP DLPI BPF link data- Introduction to Network Programming in UNIX & LINUX

Introduction to Network Programming in UNIX & LINUX

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