© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.1

ISP Services

Working at a Small-to-Medium Business or ISP – Chapter 7

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Objectives Describe the network services provided by an ISP.

Describe the protocols that support the network services provided by an ISP.

Describe the purpose, function, and hierarchical nature of the Domain Name System (DNS).

Describe and enable common services and their protocols.

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Introducing ISP ServicesCritical services for small-to-medium businesses:

Email

Web hosting

Media streaming

IP telephony

File transfer

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Introducing ISP ServicesMeeting customer requirements:

Reliability

Availability

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Protocols That Support ISP Services The TCP/IP suite of protocols supports

reliability

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Protocols That Support ISP Services Transport needs determine the choice of

Transport Layer Protocol

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Protocols That Support ISP ServicesThe TCP three-way handshake:

Synchronization

Synchronization acknowledgement

Acknowledgement

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Protocols That Support ISP ServicesHow TCP supports reliability:

Acknowledgement

Retransmission

Sequencing

Flow control

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Protocols That Support ISP Services UDP: not connection-oriented, simple protocol

Used by online games, DHCP, DNS

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Protocols That Support ISP Services TCP and UDP use ports to support multiple

services

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Protocols That Support ISP Services Socket: combination of Transport Layer port

number and Network Layer IP address of host

Socket pair: source and destination IPs and port numbers identify each conversation

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Domain Name System (DNS) Networking naming systems translate human-

readable names into machine-readable addresses

srv2

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Domain Name System (DNS)Advantages of DNS:

Hierarchical structure

Small, manageable zones

Scalable

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Domain Name System (DNS)Components of DNS:

Resource records and domain namespace

Domain name system servers

Resolvers

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Domain Name System (DNS)DNS name resolution:

Dynamic updates

Forward lookup zones

Reverse lookup zones

Primary zones

Secondary zones

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Domain Name System (DNS)Implementing DNS solutions:

ISP DNS servers

Local DNS servers

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Services and Protocols ISPs provide many business-oriented services

Secure versions of Application Layer protocols support customer security requirements

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Services and Protocols HTTP is a request-response protocol

HTTPS adds authentication and encryption

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Services and Protocols FTP uses a protocol interpreter (PI) and data

transfer process (DTP)

Two connections: one to send commands, one for actual file data transfer

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Services and Protocols SMTP: specific message format and processes

running on both client and server

POP3: mail is downloaded from server to client and then deleted

IMAP4: keeps messages on server

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Summary TCP and UDP use port numbers to provide multiple

services to hosts.

DNS uses a hierarchical system of databases to resolve names and IP addresses of known hosts within networks and across the Internet.

The most common services used on the Internet include FTP, FTPS, HTTP, HTTPS and SMTP.

ISPs use high-performance servers to support these services.

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