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14. Internetworking14. Internetworking

2Prof. Sang-Jo Yoo

ContentsContents

Internetworking Terms Principles of Internetworking Connectionless Internetworking The Internet Protocol Routing Protocols IPv6(IPNG)

3Prof. Sang-Jo Yoo

MIME

BGP FTP HTTP SMTP TELNET SNMP

UDP

ICMP OSPF

IP

TCP

Internetworking protocols in context within the TCP/IP protocol

BGP = border gateway protocolFTP = file transfer protocolHTTP=hypertext transfer protocolICMP=internet control message protocolIP = internet protocolOSPF= open shortest path first

MIME= Multi-purpose internet mail extensionSMTP = simple mail transfer protocolSNMP= simple network management protocolTCP = transmission control protocolUDP = user datagram protocol

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Internetworking termsInternetworking terms

Communication Network A facility that provides a data transfer service among devices

attached to the network. Internet

A collection of communication networks interconnected by bridges and/or routers.

Intranet Operates within the organization for internal purpose.

End system A device used to connect one of networks.

Intermediate System A device used to connect two networks.

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Internetworking termsInternetworking terms

Intermediate System Layer 1 : Repeaters copy individual bits between cable segments

Layer 2 : Bridges store and forward data link frames between LANs

Layer 3 : Multi-protocol Routers forward packets between dissimilar networks

Layer 4 : Transport Gateways connect byte streams in the transport layer

Above Layer 4 : application Gateways allow internetworking above layer 4

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Principles of InternetworkingPrinciples of Internetworking Requirements of internetwork service: provide

a link between networks. At minimum, a physical and link control connection is needed

the routing and delivery of data between processes on different networks

an accounting service internetworking facility must accommodate a number of

differences among networks different addressing schemes different maximum packet size different network-access mechanism different timeouts Error recovery/status reporting/ routing tech./user access control connection, connectionless

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The TCP/IP Internet: Internet Hierarchy

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Architectural approaches two dimensions for describing the internetworking function

the mode of operation(connection-mode or connectionless) the protocol architecture

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Internetwork architectures

Sharing protocol of the end systems

a) Connection modeNetwork layer(N)

b) Connectionless modeInternet Protocol(I)

c) Bridgedata link layer(M)

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Connection OrientedConnection Oriented

Assume that each network is connection oriented IS connect two or more networks

IS appear as DTE to each network Logical connection set up between DTEs

Concatenation of logical connections across networks

Individual network virtual circuits joined by IS

May require enhancement of local network services 802, FDDI are datagram services

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Connection Oriented IS FunctionsConnection Oriented IS Functions

Relaying Routing

e.g. X.75 used to interconnect X.25 packet switched networks

Connection oriented not often used (IP dominant)

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Connectionless OperationConnectionless Operation

Corresponds to datagram mechanism in packet switched network

Each NPDU treated separately Network layer protocol common to all DTEs and routers

Known generically as the internet protocol

Internet Protocol One such internet protocol developed for ARPANET RFC 791 Lower layer protocol needed to access particular network

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Connectionless InternetworkingConnectionless Internetworking

Advantages Flexibility Robust No unnecessary overhead

Unreliable Not guaranteed delivery Not guaranteed order of delivery

Packets can take different routes

Reliability is responsibility of next layer up (e.g. TCP)

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Combining Services

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Design Issues of IP-controlled Design Issues of IP-controlled InternetInternet

Routing Datagram lifetime Fragmentation and re-assembly Error control Flow control

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RoutingRouting

End systems and routers maintain routing tables Indicate next router to which datagram should be sent Static

May contain alternative routes

Dynamic Flexible response to congestion and errors

Source routing Source specifies route as sequential list of routers to be followed Security Priority

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Datagram LifetimeDatagram Lifetime

Datagrams could loop indefinitely Consumes resources Transport protocol may need upper bound on datagram life

Datagram marked with lifetime Time To Live field in IP Once lifetime expires, datagram discarded (not forwarded) Hop count

Decrement time to live on passing through a each router

Time count Need to know how long since last router

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Fragmentation and Fragmentation and Re-assemblyRe-assembly

Different packet sizes When to re-assemble

At destination Results in packets getting smaller as data traverses internet

Intermediate re-assembly Need large buffers at routers Buffer space will be used up storing partial datagrams. All fragments must go through same router

Inhibits dynamic routing

IP re-assembles at destination only

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Error ControlError Control

Not guaranteed delivery Router should attempt to inform source if packet discarded

Because of time to live expiring Congestion FCS errors

Source may modify transmission strategy May inform high layer protocol

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Flow ControlFlow Control

Allows routers and/or stations to limit rate of incoming data

Limited in connectionless systems Send flow control packets

Requesting reduced flow

e.g. ICMP

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The Internet ProtocolThe Internet Protocol

Internet Protocol (IP) Isolates the transport and application protocols from the messy

details of each network.

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IP services the interface with a higher layer(e.g. TCP) Send primitive - used to request transmission of a data unit Deliver primitive - used to notify a user of the arrival of a data unit

Send ( Source Address Destination Address Protocol Type of service indicators Identifier Don’t-fragment identifier Time to live Data length Option data Data )

Deliver ( Source Address Destination Address Protocol Type of service indicators

Data length Option data Data )

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Type of service indicator requests particular QoS and guides routing decision

precedence - a measure of datagram’s relative importance (8 levels) reliability (normal or high) delay throughput

the options parameter security source routing route recording stream identification timestamping

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IP Protocol

IP header

IHL : internet header length in 32-bit words, minimum is 5,(20 octets)Flag(3 bits) : More bit, Don’t fragment bit and last 1 bit is reservedProtocol : indicates the next higher level protocol at the destinationpadding(variable) : used to ensure that the datagram header is a multiple of 32 bits

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IP address 32 bit (network id + host id)

Special IP address0.0.0.0 this host255.255.255.255 broadcast on LAN127.x.x.x Loopback

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

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Technically, TCP/IP addresses identify interfaces, not system. In most cases, hosts have but a single interface. Routers usually support multiple interfaces

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Type of addresses Unicast addresses: refer to a single interface; network takes

responsibility for delivering the message to that interface. Multicast addresses: identify sets of interfaces.

This function lets a system generate a message once and delivered to many different recipients.

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Anycast addresses: refers to one of a set of interfaces New feature with IPv6. Includes many interfaces from different systems The network considers its work complete when it delivers the

message to any of the appropriate interfaces.

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Subnets and Subnet MasksSubnets and Subnet Masks

Allow arbitrary complexity of internetworked LANs within organization

Insulate overall internet from growth of network numbers and routing complexity

Each LAN assigned subnet number Host portion of address partitioned into subnet number and

host number Local routers route within subnetted network Subnet mask indicates which bits are subnet number and

which are host number

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Subnet mask of R1 and R211111111.11111111.11111111.11100000255.255.255.224Terminal B IPx.x.x.00111001 (192.228.17.57)After maskingSubnet : 1Host 25

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The Internet Control Message Protocol(ICMP) ICMP provides feedback about problems in communication

environment. ICMP is a user of IP ( not reliable) ICMP message

Destination unreachable Time exceeded Parameter problem - syntactic or semantic error in an IP Source quench - flow control (rate control) Redirect - redirect routing Echo/echo-reply - testing that communication is possible Timestamp /Timestamp reply - sampling the delay characteristics of

the internet Address mark / Address mark reply

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ICMP message format

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IPv6(IPNG)IPv6(IPNG)

History IPv4 : the present IP

32-bit address system cannot accommodate the rapidly increasing IP address demands

IPv5 : experimental real-time Stream Protocol, a connection-oriented internet level protocol

IPv6 : IPNG (IETF: internet engineering task force) Call for Proposal June, 1992 (RFC 1550) “The Recommendation for the IP Next Generation Protocol”,

Jan,1995 (RFC 1883 ~ RFC 1887)

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IPv6 Enhancements over IPv4 Expanded address space

128-bit address

Improved Option Mechanism simplify the protocol, to allow routers to process packets faster

Increased Address Flexibility anycast , multicast

Support for Resource allocation pay more attention to type of service, particularly for real-time data

Security Capabilities authentication, privacy

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IPv6 Structure

define special options that require hop-by-hop processing

extended routing, similar source routing

packet integrity and authentication

privacy

IPv6 packet with all extension header

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IPv6 Header