© 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 Work for an ISP?  It is likely that in your career as a network technician/administrator that you will be employed, or work closely with, an ISP.  In the United States, it is estimated that “Internet service providers, Web search portals, and data processing services are expected to experience 28 percent growth in wage and salary employment between 2004 and 2014, faster than the 14 percent projected for the economy as a whole.”  It is interesting to look at where the bulk of the jobs are located.

4 © 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 ISP from BLS

5 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introducing ISP Services Meeting customer requirements:  Reliability  Availability

6 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public CoLo or not to CoLo  Why might a company choose to co-locate their server or servers with an ISP?  Why might they choose to maintain the server at their own premises?

7 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  The TCP/IP suite of protocols supports reliability

8 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  Transport needs determine the choice of Transport Layer Protocol

9 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Why the TCP/IP protocol ?  The TCP/IP protocol was written to meet a specific set of conditions proposed by the Department of Defense in the late 1960’s. At this time, the United States was engaged in a “cold war” with the Soviet Union where both sides were capable of launching a nuclear strike.  The Department of Defense wanted their military sites to continue to communicate with one another in the event of a nuclear strike, even if that strike were to destroy 7/8ths of the network.

10 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Development rules  The development rules proposed by the government included: 1. A completely decentralized protocol with no key central installation that could be destroyed and bring down the whole network. 2. Fully redundant and able to continue communication between any two points even though the intermediate sites and links might stop functioning during the conversation. 3. Flexible as to handling a range of applications for the network (file transfer to time sensitive data such as voice). ¹

11 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services The TCP three-way handshake:  Synchronization  Synchronization acknowledgement  Acknowledgement

12 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services How TCP supports reliability:  Acknowledgement  Retransmission  Sequencing  Flow control

13 © 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

14 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public TCP Segment vs UDP Datagram

15 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Protocols That Support ISP Services  TCP and UDP use ports to support multiple services

16 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Queues

17 © 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

18 © 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

19 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Hosts file is like a phonebook  It is amazing to think that originally host names were maintained manually, and that as changes were made administrators had to consult published lists and add those devices to their lists, then as more devices were added repeat this process over and over and over.  As the Internet grew it would have been impossible for a human to process the changes as fast as they occurred.

20 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Hosts file is like a phonebook  It might be helpful to think about the HOSTS file like it was an address and phone book. When you type in an address, for example the HOSTS file is checked to see if you already have the ip address (i.e. the telephone number) of that site.  If you don’t have that phone number in your HOSTS file then your computer asks the ISP for the phone number, gets the address, and connects you to that site.

21 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Host Name Resolution Process

22 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) Advantages of DNS:  Hierarchical structure  Small, manageable zones  Scalable

23 © 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

24 © 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

25 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Domain Name System (DNS) Implementing DNS solutions:  ISP DNS servers  Local DNS servers

26 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public What Is a Domain Namespace? Root Domain Subdomain Second-Level Domain Top-Level Domain FQDN: SERVER1.sales.south.nwtraders.com FQDN: SERVER1.sales.south.nwtraders.com south nwtraders com sales west east org net Host: SERVER1

27 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public What Are the Components of a DNS Solution? DNS Servers on the Internet DNS Servers DNS Clients Root “.”.com.edu Resource Record Resource Record Resource Record Resource Record

28 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How Recursive Queries Work DNS Client mail1.contoso. msft A recursive query is sent to a DNS server and requires a complete answer Database Local DNS Server

29 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How Iterative Queries Work An iterative query directed to a DNS server may be answered with a referral to another DNS server Client Server Local DNS Server Local DNS Server Root Hint (.).com Recursive Query mail1.nwtraders.com Iterative Query Ask.com Ask nwtraders.com Authoritative Response Nwtraders.com

30 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How Forwarders Work A forwarder is a DNS server designated to resolve external or offsite DNS domain names Client Server Nwtraders.com Root Hint (.).com Iterative Query Ask.com Ask nwtraders.com Authoritative Response Forwarder Recursive query for mail1.nwtraders.com Recursive Query Local DNS Server Local DNS Server

31 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How Conditional Forwarding Works ISP DNS All other DNS domains Local DNS Contoso.msft DNS Contoso.msft DNS contoso.msft Query for Conditional forwarding forwards requests using a domain name condition Client Computer

32 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How Root Hints Work Root hints contain the IP addresses for DNS root servers microsoft DNS Servers DNS Server Root (.) Servers com Client Root Hints

33 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public How DNS Server Caching Works Where’s ServerA? Client1 Client2 ServerA ServerA is at Where’s ServerA? ServerA is at DNS server cache Host nameIP addressTTL ServerA.contoso.msft seconds

34 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Use a central forwarder for Internet name resolution Use conditional forwarders if you have multiple internal namespaces Consider disabling recursion for specific domains  Use a central forwarder for Internet name resolution  Use conditional forwarders if you have multiple internal namespaces  Consider disabling recursion for specific domains Best Practices for Configuring DNS ISP DNS Contoso.msft Partner Organization Northwindtraders.msft Partner Organization Northwindtraders.msft Dev.contoso.msft Root (.) Servers Forwarding with no recursion Conditional forwarding Forwarding or root hints

35 © 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

36 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Services and Protocols  HTTP is a request-response protocol  HTTPS adds authentication and encryption

37 © 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

38 © 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

39 © 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.

40 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public