DNS
This presentation is the property of its rightful owner.
Sponsored Links
1 / 24

DNS PowerPoint PPT Presentation


  • 113 Views
  • Uploaded on
  • Presentation posted in: General

DNS. DNS services Hostname to IP address translation Host aliasing Canonical and alias names Mail server aliasing Load distribution Replicated Web servers: set of IP addresses for one canonical name. DNS: Domain Name System. Root DNS Servers`. org DNS servers. edu DNS servers.

Download Presentation

DNS

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Dns

DNS


Dns domain name system

DNS services

Hostname to IP address translation

Host aliasing

Canonical and alias names

Mail server aliasing

Load distribution

Replicated Web servers: set of IP addresses for one canonical name

DNS: Domain Name System


Distributed hierarchical database

Root DNS Servers`

org DNS servers

edu DNS servers

com DNS servers

fsu.edu

DNS servers

umass.edu

DNS servers

pbs.org

DNS servers

yahoo.com

DNS servers

amazon.com

DNS servers

Distributed, Hierarchical Database


Dns root name servers

contacted by local name server that cannot resolve name

root name server:

contacts authoritative name server if name mapping not known

gets mapping

returns mapping to local name server

a Verisign, Dulles, VA

c Cogent, Herndon, VA (also Los Angeles)

d U Maryland College Park, MD

g US DoD Vienna, VA

h ARL Aberdeen, MD

j Verisign, ( 11 locations)

k RIPE London (also Amsterdam, Frankfurt)

i Autonomica, Stockholm (plus 3 other locations)

m WIDE Tokyo

e NASA Mt View, CA

f Internet Software C. Palo Alto, CA (and 17 other locations)

b USC-ISI Marina del Rey, CA

l ICANN Los Angeles, CA

DNS: Root name servers

13 root name servers worldwide


Tld and authoritative servers

TLD and Authoritative Servers

  • Top-level domain (TLD) servers: responsible for com, org, net, edu, etc, and all top-level country domains cn, ca, fr, jp, uk etc.

    • Network solutions maintains servers for com TLD

    • Educause for edu TLD

  • Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail).

    • Can be maintained by organization or service provider


Local name server

Local Name Server

  • Each ISP (residential ISP, company, university) has one.

    • Also called “default name server”

  • When a host makes a DNS query, query is sent to its local DNS server

    • Acts as a proxy, forwards query into hierarchy.


Iterative queries

iterated query:

contacted server replies with name of server to contact

“I don’t know this name, but ask this server”

local DNS server

dns.poly.edu

Iterative Queries

root DNS server

2

3

TLD DNS server

4

5

6

7

1

8

authoritative DNS server

dns.cs.umass.edu

requesting host

cis.poly.edu

gaia.cs.umass.edu


Recursive queries

root DNS server

2

3

6

7

TLD DNS server

4

local DNS server

dns.poly.edu

5

1

8

authoritative DNS server

dns.cs.umass.edu

requesting host

cis.poly.edu

gaia.cs.umass.edu

Recursive queries

recursive query:

puts burden of name resolution on contacted name server

heavy load?


Dns caching and updating records

once (any) name server learns mapping, it caches mapping

cache entries timeout (disappear) after some time

TLD servers typically cached in local name servers

Thus root name servers not often visited

DNS: caching and updating records


Dns records

DNS: distributed db storing resource records (RR)

Type=NS

name is domain (e.g. foo.com)

value is IP address of authoritative name server for this domain

RR format: (name, ttl, class, type, value

DNS records

  • Type=A

    • name is hostname

    • value is IP address

  • Type=CNAME

    • name is alias name for some “canonical” (the real) name

    • www.ibm.com is really

    • servereast.backup2.ibm.com

    • value is canonical name

  • Type=MX

    • value is name of mail server associated with name


Dns

  • Example:

    Aix 86400 IN A 192.168.42.2

    86400 IN MX 5 aix.unpbook.com.

    86400 IN MX 10 mailhost.unpbook.com.

    Aix-4 86400 IN A 192.168.42.2

    ftp 86400 IN CNAME linux.unpbook.com

    www 86400 IN CNAME linux.unpbook.com

  • DNS uses UDP to exchange information

  • Query is initiated from a system call: gethostbyname, gethostbyaddr.

  • Try ipconfig /displaydns | more on windows.


Web and http

www.someschool.edu/someDept/pic.gif

path name

host name

Web and HTTP

First some jargon

  • Web page consists of objects

  • Object can be HTML file, JPEG image, Java applet, audio file,…

  • Web page consists of base HTML-file which includes several referenced objects

  • Each object is addressable by a URL

  • Example URL:


Http overview

HTTP: hypertext transfer protocol

Web’s application layer protocol

client/server model

client: browser that requests, receives, “displays” Web objects

server: Web server sends objects in response to requests

HTTP 1.0: RFC 1945

HTTP 1.1: RFC 2068

HTTP overview

HTTP request

PC running

Explorer

HTTP response

HTTP request

Server

running

Apache Web

server

HTTP response

Mac running

Navigator


Http overview continued

Over TCP:

client initiates TCP connection (creates socket) to server, port 80

server accepts TCP connection from client

HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server)

TCP connection closed

HTTP overview (continued)


Http request message

HTTP request message

  • two types of HTTP messages: request, response

  • HTTP request message:

    • ASCII (human-readable format)

request line

(GET, POST,

HEAD commands)

GET /somedir/page.html HTTP/1.1

Host: www.someschool.edu

User-agent: Mozilla/4.0

Connection: close

Accept-language:fr

(extra carriage return, line feed)

header

lines

Carriage return,

line feed

indicates end

of message


Http request message general format

HTTP request message: general format


Http response message

HTTP response message

status line

(protocol

status code

status phrase)

HTTP/1.1 200 OK

Connection close

Date: Thu, 06 Aug 1998 12:00:15 GMT

Server: Apache/1.3.0 (Unix)

Last-Modified: Mon, 22 Jun 1998 …...

Content-Length: 6821

Content-Type: text/html

data data data data data ...

header

lines

data, e.g.,

requested

HTML file


Trying out http client side for yourself

1. Telnet to your favorite Web server:

Trying out HTTP (client side) for yourself

Opens TCP connection to port 80

(default HTTP server port) at www.cs.fsu.edu.

Anything typed in sent

to port 80 at cis.poly.edu

telnet www.cs.fsu.edu 80

  • 2. Type in a GET HTTP request:

By typing this in (hit carriage

return twice), you send

this minimal (but complete)

GET request to HTTP server

GET index.html / HTTP/1.1

Host: www.cs.fsu.edu

3. Look at response message sent by HTTP server!


Dns

telnet www.cs.fsu.edu 80

Trying 192.168.23.10...

Connected to www.cs.fsu.edu (192.168.23.10).

Escape character is '^]'.

GET /index.html /HTTP/1.1

Host: www.cs.fsu.edu

HTTP/1.1 200 OK

Date: Wed, 28 Nov 2007 18:34:29 GMT

Server: Apache/2.0.52 (Scientific Linux)

Last-Modified: Mon, 29 Aug 2005 18:02:35 GMT

ETag: "1defce0-29c5-4cd2a4c0"

Accept-Ranges: bytes

Content-Length: 10693

Connection: close

Content-Type: text/html; charset=ISO-8859-1

<html>

<head>

<title>Computer Science @ Florida State University</title>

<base HREF="http://www.cs.fsu.edu/">

<meta NAME="resource-type" CONTENT="document">

<meta NAME="description" CONTENT="Website for the Computer Science Department

at Florida State University">

<meta NAME="keywords" CONTENT="Florida State University, Computer Science,

Internet2, CS">

<meta NAME="distribution" CONTENT="global">

<meta NAME="author" CONTENT="Kendal Van Dyke">


User server state cookies

HTTP is stateless.

two requests are treated independently.

Why stateless?

What is the problem with a stateless http?

E-commence: People buy things by making many requests. Need the ability to bind the requests from the same customer together.

Solution: cookies

User-server state: cookies


Cookies keeping state cont

client

server

usual http request msg

usual http response +

Set-cookie: 1678

Cookie file

Cookie file

Cookie file

amazon: 1678

ebay: 8734

ebay: 8734

amazon: 1678

ebay: 8734

cookie-

specific

action

usual http request msg

cookie: 1678

usual http request msg

cookie: 1678

usual http response msg

usual http response msg

cookie-

spectific

action

Cookies: keeping “state” (cont.)

server

creates ID

1678 for user

entry in backend

database

access

access

one week later:


Cookies continued

What cookies can bring:

authorization

shopping carts

recommendations

user session state (Web e-mail)

Cookies (continued)

aside

  • Cookies and privacy:

  • cookies permit sites to learn a lot about you

  • you may supply name and e-mail to sites

  • search engines use redirection & cookies to learn yet more

  • advertising companies obtain info across sites


Dns

  • Some issues in HTTP:

    • Mainly due to its popularity

  • Cache support.

    • Insufficient in http/1.0, improved in http/1.1

    • Intermediate nodes, encoding, etc

  • Dynamically generated date

    • Not reliable in http/1.0

  • Performance

    • Persistent or non-persistent TCP connection

    • Download the whole file or part of a file

  • User preference

  • Security


Content distribution

Content-Distribution

  • Akamai.

  • With thousands of servers all around the world.


  • Login