internet and web services 1490

8/4/2019 Internet and Web Services 1490

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TCP/IP Internetworking


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Single Networks (Subnets)

Internets

Connect multiple single networks using routers

70%-80% of internet traffic follows TCP/IP standards

These standards are created by the IETF

Chapter 10 looks in more detail at TCP/IPmanagement


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General Purpose Layer Specific Purpose

Application-applicationcommunication

Application (5) Application-applicationinterworking

Transmission across an

internet

Transport (4) Host-host

communication

Internet (3) Packet delivery acrossan internet

Transmission across a

single network (LAN orWAN)

Data Link (2) Frame delivery across a

networkPhysical (1) Device-device

connection

TCP/IP standards dominate at theinternet and transport layerstransmission across an internet


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Transport Layerend-to-end (host-to-host)

TCP is connection-oriented, reliableUDP is connectionless and unreliable

Internet Layer(usually IP)

hop-by-hop (host-router or router-router)connectionless, unreliable

Router 1 Router 2 Router 3

Client PCServer


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Frames and Packets

Messages at the data link layer are called frames

Messages at the internet layer are called packets

Within a single network, packets are encapsulatedin the data fields of frames

FrameHeader

Packet(Data Field)

FrameTrailer


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Frames and Packets

In an internet with hosts separated by Nnetworks, there will be:

2 hosts

One packet (going all the way between hosts)

One route (between the two hosts), though thisroute may differ between connections.

N frames (one in each network)

N-1 routers (change frames between each pair ofnetworks)


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Int

App

DL

Trans

Phy

Int

Trans

IntInt

SourceHost

DestinationHost

Switch1

Switch2

Router1

Switch3

Router2

Transmission Control Protocol (TCP)Or User Datagram Protocol (UDP)

Internet Protocol(IP)

Horizontal Communication

IP

Frames and Packets


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TCP/IP Standards

5 Application

User Applications

HTTP SMTPMany

OthersDNS

RoutingProtocols

ManyOthers

Supervisory Applications

TCP UDP4 Transport

IP3 InternetMPLS

ARP

None: Use OSI Standards2 Data Link

None: Use OSI Standards1 Physical

Internetworking is done at the internet and transport layers.There are only a few standards at these layers.

We will look at the shaded protocols in this chapter.

ICMP


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IP, TCP, and UDP

Protocol Layer Connection-Oriented/CNLS

Reliable /Unreliable

Lightweight /Heavyweight

TCP 4. Trans Connection-oriented

Reliable Heavyweight

UDP 4. Trans CNLS Unreliable Lightweight

IP 3. Int CNLS Unreliable Lightweight

Note: CNLS = connectionless


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IP Addresses


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Figure 8-3: Hierarchical IP Address

128.171.17.13

Network Part (not alw ays 16 bits)

Subnet Part (not alw ays 8 bits)

Host Part (not alw ays 8 bits)

Total alw ays is 32 bits

UH Netw ork (128.171)

CBA Subnet (17)Host 13

The Internet


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Hierarchical Addressing

Hierarchical Addressing Brings Simplicity Phone System

Country code-area code-exchange-subscribernumber

01-808-555-9889

Long-distance switches near the top of the hierarchyonly have to deal with country codes and area codes to

set up circuits

Similarly, core Internet routers only have to considernetwork or network and subnet parts of packets


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Dynamic RoutingProtocols

Routing Table Information

Dynamic Routing Protocol


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Dynamic Routing Protocols

Routing

Routers constantly exchange routing table informationwith one another using dynamic routing protocols

Note that the term routing is used in two ways InTCP/IP

For IP packet forwarding and

For the exchange of routing table information

through routing protocols

Routing Table Information

Dynamic Routing Protocol


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Autonomous System

An organizations internal network (internet)

Interior Dynamic Routing Protocols Within an Autonomous System, firms use interior

dynamic routing protocols

Exterior Dynamic Routing Protocols Between Autonomous Systems, companies use an

exterior dynamic routing protocol


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Interior Dynamic Routing Protocols

As just discussed, within an Autonomous System,firms use interior dynamic routing protocols

The organization can freely select an interior routingprotocol

RIP (Routing Information Protocol)

OSPF (Open Shortest Path First)

EIGRP (Enhanced Interior Gateway RoutingProtocol)

Etc.


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Routing Information Protocol (RIP)

Simple interior dynamic routing protocol from the IETF(Internet Engineering Task Force)

Low-cost management

Poor efficiency: metric is merely the number of routerhops to the destination host

No way to select cheapest route, etc.

Weak security

Useful only in small firms


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Open Shortest Path First

Sophisticated IETF interior dynamic routing protocol

Very efficient, having a complex metric based on amixture of cost, throughput, and traffic delays

Strong security

High management costs

The only IETF dynamic routing protocol that makessense for all but the smallest networks


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Enhanced Interior Gateway Routing Protocol(EIGRP)

Proprietary interior dynamic routing protocol from

Cisco Systems

Gateway is an obsolete term for router

Very efficient because metric is a mixture of interface

bandwidth, load on the interface (0% to 100% ofcapacity), delay, and reliability (percentage of packetslost).


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Enhanced Interior Gateway Routing Protocol(EIGRP)

Only interior dynamic routing protocol that supports

multiprotocol routing (not just TCP/IP): IPX/SPX, SNA,etc.

But to use it, a company must buy Cisco routers


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Exterior Dynamic Routing Protocols

Between autonomous systems, companies use anexterior dynamic routing protocol

An organization is not free to select an exterior routingprotocol

It must select a protocol selected by its ISP

Border Gateway Protocol (BGP) is the main exteriorrouting protocol

Recall that gateway is the old term for router


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Autonomous System

Internal

Router

BGP Is an Exterior DynamicRouting ProtocolAutonomous System

RIP,OSPF, orEIGRP

RIP,OSPF, or

EIGRP

InternalRouter

Border

Router

BorderRouter

RIP, OSPF, and EIGRPInterior Dynamic Routing Protocols


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The AddressResolution Protocol

(ARP)


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Address Resolution Protocol (ARP)

OriginatingRouter

Host110.19.8.47

does not respond toARP Request.

1.

Broadcast ARP Request Message:"IP Host 110.19.8.17,

w hat is your 48-bit MAC address?"

Host110.19.8.17

replies.2.

ARP Response Message:"My MAC address is A7-23-DA-95-7C-99".

Router B110.19.8.

does not reply

ARP Cache:Know n

IP address-EthernetAddress

Pairs

Packet

Frame


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Address Resolution Protocol (ARP)

OriginatingRouter

Host110.19.8.47

does not respond toARP Request.

1.

Broadcast ARP Request Message:"IP Host 110.19.8.17,

w hat is your 48-bit MAC address?"

Host110.19.8.17

replies.2.

ARP Response Message:"My MAC address is A7-23-DA-95-7C-99".

Router B110.19.8.

does not reply

ARP Cache:Know n

IP address-EthernetAddress

Pairs

The Situation:The router wishes to pass the packet to the

destination host or to a next-hop router.The router knows the destination IP address of the target.

The router must learn the targets MAC layer address

in order to be able to send the packet to the target in a frame.The router uses the Address Resolution Protocol (ARP)

Packet

Frame


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Multiprotocol LabelSwitching (MPLS)


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Multiprotocol Label Switching (MPLS)

Routers are Connected in a Mesh

Multiple alternative routes make the choice of anoutgoing interface very expensive

PSDNs also are Arranged in a Mesh

However, a best path (virtual circuit) is set up beforetransmission begins

Once a VC is in place, subsequent frames are handledquickly and inexpensively

MPLS Does Something Like this for Routers


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MPLS Adds a Label Before Each Packet Label sits between the frame header and the IP

header

Contains an MPLS label number

Like a virtual circuit number in a PSDN frame

Label-switching router merely looks up the MPLSlabel number in its MPLS table and sends the packet

back out

Data LinkHeader

MPLSLabel

IPPacket


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Advantages of MPLS

Router does a simple table lookup. This is fast andtherefore inexpensive per packet handled

As fast as Ethernet switching!

Can use multiple label numbers to give to trafficbetween sites for multiple levels of priority or quality of

service guarantees

MPLS supports traffic engineering: balancing traffic onan internet


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Label-Sw itched

Path

Label-SwitchingRouter 1

Label-Sw itching

Router 2



Label-Sw itchingRouter 5Packet Label

Legend

Label-Sw itching TableLabelA

CF

Interface1

13

MPLS reduces forw arding costs and permits traff ic engineering,including quality of service and traffic load balancing

First routeradds the label

Last routerdrops the label


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The Internet ControlMessage Protocol

(ICMP)


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Internet Control Message Protocol (ICMP) forSupervisory Messages

RouterHost UnreachableError Message

Echo Request(Ping)

Echo

Response

IPHeader

ICMPMessage

ICMP is the supervisory protocolat the internet layer.

ICMP messages are encapsulated in thedata fields of IP packets


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Echo Request(Ping)

Echo

Response

IPHeader

ICMPMessage

When an error occurs, the devicenoting the error may try to respond with an

ICMP error message describing the problem.

ICMP error messages often are not sentfor security reasons because

attackers can use them to learn about a network


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Echo Request(Ping)

Echo

Response

IPHeader

ICMPMessage

To see if another host is active, a host

can send the target host an ICMP echo requestmessage (called a ping).

If the host is active, it will send back anecho response message confirming that it is active.

D i H C fi i P l


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Dynamic Host Configuration Protocol(DHCP)

DHCP Gives Each Client PC at Boot-Up:

A temporary IP Address

A subnet mask

The IP addresses of local DNS servers

Better Than Manual Configuration

If subnet mask or DNS IP addresses change, only the

DHCP server has to be updated manually

Client PCs are automatically updated when they nextboot up


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The InternetProtocol (IP)

Versions 4 and 6


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IPv4 and IPv6 Packets

IP Version 4 PacketVersion(4 bits)Valueis 4

(0100)

HeaderLength(4 bits)

Flags(3 bits)

Time to Live(8 bits)

Header Checksum(16 bits)

Diff-Serv(8 bits)

Total Length(16 bits)

Length in octets

Bit 0 Bit 31

Identification (16 bits)Unique value in each original

IP packet

Fragment Offset (13 bits)Octets from start of

original IP fragmentsdata field

Protocol (8 bits)1=ICMP, 6=TCP,

17=UDP


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(0100)


Flags(3 bits)



Diff-Serv(8 bits)


Length in octets

Bit 0 Bit 31


IP packet




17=UDP

IPv4 is the dominant version of IP today.The version number in its header is 4 (0100).

The header length and total length field tell the size of the packet.

The Diff-Serv field can be used for quality of service labeling.(But MPLS is being used instead by most carriers)


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(0100)


Flags(3 bits)



Diff-Serv(8 bits)


Length in octets

Bit 0 Bit 31


IP packet




17=UDP

The second row is used for reassembling fragmentedIP packets, but fragmentation is quite rare,

so we will not look at these fields.


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IP Version 4 Packet

Version(4 bits)Value

is 4(0100)


Flags(3 bits)



Diff-Serv(8 bits)


Length in octets

Bit 0 Bit 31


IP packet


original IP fragments

data field


17=UDP

The sender sets the time-to-live value (usually 64 to 128).

Each router along the way decreases the value by one.A router decreasing the value to zero discards the packet.It may send an ICMP error message.

The protocol field describes the message in the data field(ICMP, TCP, UDP, etc.)

The header checksum is used to find errors in the header.If a packet has an error, the router drops it.

There is no retransmission at the internet layer,so the internet layer is still unreliable.


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IP Version 4 Packet

Source IP Address (32 bits)

Bit 0 Bit 31

Destination IP Address (32 bits)

PaddingOptions (if any)

Data Field

The source and destination IP addressesAre 32 bits long, as you would suspect.

Options can be added, but these are rare.


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IP Version 6 Packet

Source IP Address (128 bits)

Bit 0 Bit 31

Hop Limit(8 bits)

Next Header(8 bits) Nameof next header

Payload Length(16 bits)

Version(4 bits)Valueis 6

(0110)

Diff-Serv(8 bits)

Flow Label (20 bits)Marks a packet as part of a specific flow

Destination IP Address (128 bits)

Next Header or Payload (Data Field)

IP Version 6 is the emergingversion of the Internet protocol.

Has 128 bit addresses foran almost unlimited number of IP addresses.

Growing fastest in Asia, which wasshort-changed in IPv4 address allocations


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The TransmissionControl Protocol

(TCP)


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TCP Segment and UDP Datagram

TCP Segment

Window Size(16 bits)

Bit 0 Bit 31

Destination Port Number (16 bits)Source Port Number (16 bits)

Sequence Number (32 bits)

Acknowledgment Number (32 bits)

Urgent Pointer (16 bits)TCP Checksum (16 bits)


Reserved(6 bits)

Flag Fields(6 bits)

Flag fields are one-bit fields. They include SYN, ACK, FIN,and RST.

The source and destination port numbersspecify a particular application on the

source and destination multitasking computers

(Discussed later)

Sequence numbers are 32 bits long.So are acknowledgment numbers.


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TCP Segment


Bit 0 Bit 31





HeaderLength

(4 bits)

Reserved(6 bits)

Flag Fields(6 bits)

Flags are one-bit fields.If a flags value is 1, it is set.

If a flags value is 0, it is not set.TCP has six flags

If the TCP Checksum fields value is correct,The receiving process sends back an acknowledgment.


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TCP Segment


Bit 0 Bit 31





HeaderLength

(4 bits)

Reserved(6 bits)

Flag Fields(6 bits)

For flow control (to tell the other party to slow down),The sender places a small value in the Window Size field.

If the Window Size is small, the receiver will have to stop transmittingafter a few more segments (unless it gets a new acknowledgment

extending the number of segments it may send.)


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TCP SegmentBit 0 Bit 31

PaddingOptions (if any)

Data Field

TCP segment headers can end with options.This is very common.

If an option does not end at a 32-bit boundary,padding must be added.


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The User DatagramProtocol (UDP)


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UDP DatagramBit 0 Bit 31

Source Port Number (16 bits) Destination Port Number (16 bits)

UDP Length (16 bits) UDP Checksum (16 bits)

Data Field

UDP messages (datagrams) are very simple.

Like TCP, UDP has 16-bit port numbers.

The UDP length field allows variable-length application messages.If the UDP checksum is correct, there is no acknowledgment.

If the UDP checksum is incorrect, the UDP datagram is dropped.


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TCP Connection Openings and Closings

TCP is a connection-oriented protocol

Each connection has a formal opening process

Each connection has a formal closing process

During a connection, each TCP segment isacknowledged

(Of course, pure acknowledgments are not

acknowledged)



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SYN

SYN/ACK

ACK

Normal Three-Way Opening

A SYN segment is a segment in which the SYN bit is set.One side sends a SYN segment requesting an opening.The other side sends a SYN/acknowledgment segment.

Originating side acknowledges the SYN/ACK.



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FIN

ACK

FIN

ACK

Normal Four-Way Close

A FIN segment is a segment in which the FIN bit is set.Like both sides saying good bye to end a conversation.



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RST

Abrupt Reset

An RST segment is a segment in which the RST bit is set.A single RST segment breaks a connection.

Like hanging up during a phone call.There is no acknowledgment.


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Layer 3 Switches

Layer 3 Switches and Routers in Site


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Layer 3 Switches and Routers in SiteNetworks

Router

Ethernet WorkgroupSw itch

ToOtherSites

Layer 3Sw itch

L3

L3

Layer 3 sw itches arerouters.

Layer 3 sw itches arefaster and cheaper tobuy than traditionalrouters.

How ever, they areusually limited infunctionality.

They also areexpensive to manage.

They are typicallyused between

Ethernet Workgroup

Sw itch

Layer 3Sw itch

Usually too expensive to replace workgroup switches.Usually too limited in functionality to replace border routers.

Replaces core switches in the middle.


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Web Services

W b S i


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Web Services

Similar to the old client server architecture of earlyLAN systems, but services are now provided byinternet or web based resources.

SOA (Service Oriented Architecture) is used toenable platform and development languageindependence.

W b S i


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Web Services

W b S i
http://upload.wikimedia.org/wikipedia/commons/d/d4/SOA_Elements.png


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Web Services

Web services may be simple or complex

Example: RSS


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The Domain NameSystem (DNS)

Figure 8-14: Domain Name System (DNS)


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g y ( )Hierarchy

(root)

cnn.commicrosoft.comhawaii.edu

.com .uk.ie.edu .net

Top-LevelDomainNames

Second-LevelDomainNames

Subnet Namecba.hawaii.edu

voyager.cba.haw aii.edu ntl.cba.haw aii.eduHost Names

.nl.org .au

A domain is a group of resourcesunder the control of an organization.

The domain name system is ageneral system for managing names.

It is a hierarchical naming system.

Queries to a DNS server can getInformation about a domain.



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g y ( )Hierarchy

(root)







.nl.org .au

The highest level is called the root.There are 13 DNS Root Servers.They point to lower-level servers.



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g y ( )Hierarchy

(root)







.nl.org .au

Top-level domains aregeneric TLDs (.com, .net., .org, etc.) or

country TLDs (.ca, .uk, .ie, etc.)



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g y ( )Hierarchy

(root)







.nl.org .au

Organizations seekgood second-level domain

names

cnn.commicrosoft.com

hawaii.eduetc.

Get them from

address registrars



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Hierarchy

(root)







.nl.org .au

Host names are the bottomof the DNS hierarchy.

A DNS request for a host namewill return its IP address.

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