Networking

Taekyung Kim

0x410 ~ 0x430

2014. 11. 20

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OSI Model

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OSI 7 Layers

• International Standards Organization (ISO) is a multina-tional body dedicated to worldwide agreement on inter-national standards. – Almost three-fourths of countries in the world are

represented in the ISO.

• An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. – It was first introduced in the late 1970s.

• The OSI model is a layered framework for the design of network systems that allows communication between all types of computer systems

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OSI 7 Layers

• Physical: transmit bits over a medium• Data link: organize bits into a frame• Network: move packets from source to destina-

tion• Transport: provide reliable process-to-process

message delivery• Session: establish, manage, and terminate ses-

sions• Presentation: translate, encrypt and compress

data• Application: allow access to the network re-

sources

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OSI 7 Layers

• Encapsulation

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OSI 7 Layers

• Message Propagation

Client ServerRouter A Router B

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Physical Layer

• The physical layer consists of the basic network-ing hardware transmission technologies of a net-work

• The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium

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Data Link Layer

• The data link layer is the protocol layer that transfers data between nodes on the same LAN segment

• Data link layer services– Encapsulation of network layer data packets into

frames– Frame synchronization– Logic link control sublayer

• Error control (ARQ)• Flow control

– Media access control (MAC) sublayer• Multiple access protocols for channel-access control (e.g.

CSMA/CD, CSMA/CA)• Physical addressing (MAC addressing)• LAN switching (packet switching)• Data packet queuing or scheduling

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Data Link Layer

• Address Resolution Protocol (ARP)– is used to convert an IP address to a MAC ad-

dress

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Network Layer

• The network layer is responsible for packet forward-ing including routing through intermediate routers

• Protocols– IPv4 / IPv6: Internet Protocol– ICMP: Internet Control Message Protocol– ARP: Address Resolution Protocol– IGMP: Internet Group Management Protocol– PIM-SM: Protocol Independent Multicast Sparse

Mode– PIM-DM: Protocol Independent Multicast Dense

Mode– RIP: Routing Information Protocol

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Network Layer

• IPv4 Header Format

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Network Layer

• IPv4 Fragmentation– Separated into MTU

(maximum transmis-sion unit) size

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Network Layer

• Internet Control Message Protocol (ICMP)– is used by network devices, like routers, to

send error message indicating• for example a requested service is not available or a

host or router could not be reached

– is assigned protocol number 1• But it is still network layer protocol

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Network Layer

• Internet Control Message Protocol (Cont’d)– Ping

• operates by sending ICMP echo request packets to the target host and waiting for an ICMP echo re-sponse

– Traceroute

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Transport Layer

• A transport layer provides end-to-end communi-cation services for applications

• Transport layer services– Same order delivery

• Segment numbering

– Reliability• ACK message

– Flow control– Congestion avoidance– Multiplexing

• Ports

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Transport Layer

• TCP Header Format

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Transport Layer

• TCP Three Way Handshaking

Connectionopened

PassiveopenActive

open

SYN

UAPRS F

seq: 8000

SYN +ACKUAPRS F

seq: 15000

ack: 8001rwnd: 5000

ACK

UAPRS F

seq: 8000ack: 15001

rwnd: 10000

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Transport Layer

• TCP Congestion Control

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Socket

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Socket

• A socket is an endpoint of an inter-process com-munication flow across a computer network– A socket address is the combination of an IP

address and a port number• (src_ip, src_port, dst_ip, dst_port)

– Based on this address, sockets deliver incom-ing data packets to the appropriate application process or thread

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Socket API

• Header files– <sys/socket.h>

• Core Berkely Software Distribution (BSD) socket func-tions and data structures

– <netinet/in.h>• AF_INET and AF_INET6 address families

– <arpa/inet.h>• Functions for manipulating numeric IP addresses

– <netdb.h>• Functions for translating protocol names and host

names into numeric addresses

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Socket API

• socket(int domain, int type, int protocol)– creates a new socket of a certain socket type

and allocates system resources to it• connect(int fd, struct sockaddr *remote_host,

socklen_t addr_length)– is used on the client side, and assigns a free

local port number to a socket– attempts to establish a new TCP connection

• bind(int fd, struct sockaddr *remote_host, socklen_t addr_length)– is used on the server side, and associates a

socket with a socket address structure

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Socket API

• listen(int fd, int backlog_queue_size)– is used on the server side, and causes a bound

TCP socket to enter listening state– store requests into a backlog queue

• accept(int fd, struct sockaddr *remote_host, socklen_t *addr_length)– is used on the server side– accepts a received incoming attempt to create

a new TCP connection from the remote client• send(), recv(), write(), read(), sendto(), recvfrom()

– are used for sending and receiving data to/from a remote host

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Socket API

• socket(int domain, int type, int protocol)– Domain

• AF_INET: IPv4• AF_INET6: IPv6

– Type• SOCK_STREAM: reliable stream• SOCK_DGRAM: datagram service• SOCK_RAW: raw protocols

– Protocol• IPPROTO_TCP, IPPROTO_UDP, IPPROTO_RAW, and so

on• The value ‘0’ is used to select a default protocol from

the selected domain and type

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Socket API

• AF_INET v.s. PF_INET– At socket.h

• /* Protocol families. */• #define PF_INET 2 /* IP protocol family. */• /* Address families. */• #define AF_INET PF_INET

– The current POSIX.1-2008 specification doesn’t specify any of PF_-constants, but only AF_- constants

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Socket API

• htonl(), htons(), ntohl(), ntohs()– convert values between host and network byte

order– On the i386 the host byte order is LSB first,

whereas the network byte order is MSB first

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Socket API

• inet_aton(), inet_ntoa()– Internet address manipulation routines– inet_aton() converts the Internet host address,

given in IPv4 dotted notation, to a network bytes

– inet_ntoa() converts the Internet host address, given in network byte order, to a string in IPv4 dotted notation

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simple_server.c

• Create a socket– SO_REUSEADDR option

• the socket can be successfully bound unless there is a conflict with another socket bound to exactly the same combination of source address and port

• Specify the address

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simple_server.c

• Bind the socket

• Accept a connection and print received bytes

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simple_server.c

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host_lookup.c

• Well-known ports– The port numbers in the range from 0 to 1023

are the well-known ports– They are used by system processes that pro-

vide widely used types of network services– Example

• 20: ftp-data• 21: ftp-command• 22: ssh• 23: telnet• 80: http• 443: https

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host_lookup.c

• HTTP HEAD Command

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host_lookup.c

• gethostbyname(const char *name)– returns a structure of type hostent for the

given host name– name can be either a hostname or an IPv4 ad-

dress in dot notation or IPv6 address in colon notation

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host_lookup.c

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webserver_id.c

• Get webserver id by using a HTTP HEAD com-mand

• Get host address

• Send a HTTP GET command and filter received data

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webserver_id.c

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tinyweb.c

• Handle HTTP GET and HTTP HEAD command• Open a socket with an 80 (HTTP) port

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tinyweb.c

• handle_connection()

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tinyweb.c

• handle_connection() (Cont’d)

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tinyweb.c

• ./webserver_id localhost

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tinyweb.c

• Web Browser Test

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THANK YOU!