© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 4.1 ISP Services Working at a Small-to-Medium Business or ISP – Chapter 7

2 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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.

3 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introducing ISP Services Critical services for small-to-medium businesses:   Web hosting  Media streaming  IP telephony  File transfer

4 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introducing ISP Services Meeting customer requirements:  Reliability  Availability

5 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  The TCP/IP suite of protocols supports reliability

6 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  Transport needs determine the choice of Transport Layer Protocol

7 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services The TCP three-way handshake:  Synchronization  Synchronization acknowledgement  Acknowledgement

8 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services How TCP supports reliability:  Acknowledgement  Retransmission  Sequencing  Flow control

9 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  UDP: not connection-oriented, simple protocol  Used by online games, DHCP, DNS

10 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  TCP and UDP use ports to support multiple services

11 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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

12 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS)  Networking naming systems translate human- readable names into machine-readable addresses srv2

13 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) Advantages of DNS:  Hierarchical structure  Small, manageable zones  Scalable

14 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) Components of DNS:  Resource records and domain namespace  Domain name system servers  Resolvers

15 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) DNS name resolution:  Dynamic updates  Forward lookup zones  Reverse lookup zones  Primary zones  Secondary zones

16 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) Implementing DNS solutions:  ISP DNS servers  Local DNS servers

17 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Services and Protocols  ISPs provide many business-oriented services  Secure versions of Application Layer protocols support customer security requirements

18 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Services and Protocols  HTTP is a request-response protocol  HTTPS adds authentication and encryption

19 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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

20 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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

21 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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.

22 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public