Network Services1-1 Overview of Internet and Network Services ECE7610/ECE7650

Network Services 1-1

Overview of Internet and Network Services

ECE7610/ECE7650



What’s the Internet: “nuts and bolts” view

millions of connected computing devices: hosts = end systems

running network apps communication links

fiber, copper, radio, satellite

transmission rate = bandwidth

routers: forward packets (chunks of data)

local ISP

companynetwork

regional ISP

router workstation

servermobile


What’s the Internet: a service view Distributed applications:

Web, email, games, e-commerce, file sharing

Network protocols: used by applications to control sending, receiving of msgs: TCP, IP, HTTP, FTP, PPP Internet standards

• RFC: Request for comments• IETF: Internet Engineering Task

Force

Communication services provided to apps: Connectionless unreliable connection-oriented reliable


A closer look at network structure: network edge:

applications and hosts network core:

routers network of networks

access networks, physical media: communication links


The network edge: end systems (hosts):

run application programs e.g. Web, email at “edge of network”

Programs in end-systems use the serivce of the Internet to send msgs to each other client/server model

• client host requests, receives service from always-on server; e.g. web, email

peer-peer model:• minimal (or no) use of dedicated

servers• e.g. Gnutella, KaZaA, Skype, BitTorrent


The Network Core

Physical connectivity of local area networks mesh of interconnected

routers Logical connectivity:

how is data transferred through net?


Internet structure: network of networks

“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

NAPs (Network Access Points) are complex high-speed switching networks often concentrated at a single building. Operated by 3rd party telecom or Internet backbone ISP-1.

PoPs (Points of Presence) are private group of routers within each ISP and used to connect it (peer it) with other up/down/equal ISPs and is the new trend in connectivity.

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet, tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect at public NAPs or private POPs.


Internet structure: network of networks

“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet


Tier-1 ISP: e.g., Sprint

Sprint US backbone network

Seattle

Atlanta

Chicago

Roachdale

Stockton

San Jose

Anaheim

Fort Worth

Orlando

Kansas City

CheyenneNew York

PennsaukenRelay

Wash. DC

Tacoma

DS3 (45 Mbps)OC3 (155 Mbps)OC12 (622 Mbps)OC48 (2.4 Gbps)


ATT Global Backbone IP Network

From http://www.business.att.com


MichNet: Statewide Backbone Nation’s longest-

running regional network

An 2.5 Gigabit (OC48c) backbone, with 24 backbone nodes

Two diverse 2.5 gigabit (2x OC48) to chicago

www.merit.edu/mn


Internet protocol stack application: supporting network

applications FTP, SMTP, HTTP

transport: process-process data transfer TCP, UDP

network: host-host data transfer IP

link: data transfer between neighboring network elements PPP, Ethernet

physical: bits “on the wire”

application

transport

network

link

physical


messagesegment

datagram

frame

sourceapplicatio

ntransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHnHl M

HtHn M

HtHnHl M HtHnHl M

router

switch

Encapsulation

Characteristics of Layering

Layering positives: Each layer relies on services from layer

below and exports services to layer above Interface defines interaction Hides implementation - layers can change

without disturbing other layers (black box)

Layering negatives: duplicate functionality and inter-dependency.


Network Services 16

Examples of Network Services E-mail Web Instant messaging Remote login P2P file sharing Multi-user network

games Streaming stored

video clips

Internet telephone Real-time video

conference Massive parallel

computing

Network Services 17

Creating a network app

Write programs that run on different end

systems and communicate over a

network. e.g., Web: Web server

software communicates with browser software

little software written for devices in network core network core devices do

not run user application code

application on end systems allows for rapid app development, propagation

applicationtransportnetworkdata linkphysical



Network Services 18

Application architectures

Appl arch is designed by appl developers and dictates how the appl is organized over various end-systems

Types of organizations: Client-server (thin vs thick client) Peer-to-peer (P2P) Hybrid of client-server and P2P

Network Services 19

Client-server architectureserver:

waits to be contacted always-on have permanent IP

address server farms for scaling

clients: initiates communication can be thin (browser-only)

or thick (need more than a browser)

not always-on may have dynamic IP

addresses do not communicate

directly with each other

Client/Server

Web Server(e.g. IIS,Apache)

Application Server(e.g. WebSphere)

Database Server(e.g. DB2, Oracle)

Client/Client/Server

Google Data Centers

Estimated cost of data center: $600M Google spent $2.4B in 2007 on new

data centers Each data center uses 50-100

megawatts of power

1-20Network Services

Network Services 21

Pure P2P architecture

server is not always-on arbitrary end systems

directly communicate, without passing through special servers

peers are intermittently connected and change IP addresses

examples: Gnutella, KaZaa, Bitorrent

Highly scalableBut difficult to manage

P2P file sharing accounts for a major portion of all traffic

Network Services 22

Hybrid of client-server and P2PNapster Bitorrent

File transfer P2P File search centralized:

• Peers register content at central server• Peers query same central server to locate content

Instant messaging Chatting between two users is P2P Presence detection/location centralized:

• User registers its IP address with central server when it comes online

• User contacts central server to find IP addresses of buddies

Network Services 23

Processes communicating

Process: program running within a host. within same host, two processes

communicate using inter-process communication (IPC) (defined by OS).

processes in different hosts communicate by exchanging messages

A network appl consists of pairs of processes that send messages to each other over a network The process initiating the comm is labeled as client,

and the other waiting to be connected as server Applications with P2P architectures have

client processes & server processes A process assumes client and server roles in diff

time

Network Services 24

Sockets process sends/receives

messages to/from its socket socket analogous to door

sending process shoves msg out door

sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process

Interface between the appl and transport layer within a host

process

TCP withbuffers,variables

socket

host orserver

process

TCP withbuffers,variables

socket

host orserver

Internet

controlledby OS

controlled byapp developer

Socket API available for developers: (1) choice of transport protocol; (2) ability to fix a few parameters. Everything else handled by the OS

Process naming: host IP addr + port number.

Network Services 25

Application layer protocol defines Types of messages

exchanged, e.g., request & response messages

Syntax of message types: what fields in messages & how fields are delineated

Semantics of the fields, i.e., meaning of information in fields

Rules for when and how processes send & respond to messages

Public-domain protocols:

defined in RFCs allows for

interoperability e.g., HTTP, SMTPProprietary protocols: e.g., KaZaA

Appl-layer protocol is one pieceof a network appl.

Network Services 26

What services does an application need?Data loss (Reliable transfer) some apps (e.g., audio) can

tolerate some loss other apps (e.g., file transfer,

telnet) require 100% reliable data transfer

Timing some apps (e.g., Internet

telephony, interactive games) require low delay to be “effective” (hard real-time)

Examples: no real-time (soft real-time)?

Bandwidth some apps (e.g.,

multimedia, bw-sensitive appl) require minimum amount of bandwidth to be “effective”

other apps (“elastic apps”) make use of whatever bandwidth they get. Exampes ??

Network Services 27

Service requirements of common apps

Application

file transfere-mail

Web documentsreal-time audio/video

stored audio/videointeractive gamesinstant messaging

Data loss

no lossno lossno lossloss-tolerant

loss-tolerantloss-tolerantno loss

Bandwidth

elasticelasticelasticaudio: 5kbps-1Mbpsvideo:10kbps-5Mbpssame as above few kbps upelastic

Time Sensitive

nononoyes, 100’s msec

yes, few secsyes, 100’s msecyes and no

Network Services 28

Internet transport protocols services

TCP service: connection-oriented: setup

required between client and server processes

reliable transport between sending and receiving process

flow control: sender won’t overwhelm receiver

congestion control: throttle sender when network overloaded

does not providing: timing, minimum bandwidth guarantees

UDP service: unreliable data transfer

between sending and receiving process

does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee

Q: why bother? Why is there a UDP?

Network Services 29

Internet apps: application, transport protocols

Application

e-mailremote terminal access

Web file transfer

streaming multimedia

Internet telephony

Applicationlayer protocol

SMTP [RFC 2821]Telnet [RFC 854]HTTP [RFC 2616]FTP [RFC 959]proprietary(e.g. RealNetworks)proprietary(e.g., Dialpad)

Underlyingtransport protocol

TCPTCPTCPTCPTCP or UDP

typically UDP

Real-time applications are often run in UDP:they can tolerate some loss, butrequire a minimal rate

Network Services 30

Examples of Network Services E-mail Web and DNS Instant messaging Remote login P2P file sharing Multi-user network


video clips



computing

Network Services 31

Web and HTTP

Web Application Client-server appl that allows clients to

obtain documents from web servers on demand

Components: • HTML document format• Web browsers: e.g. IE, firefox• Web servers: e.g Apache, • Appl-layer protocol: HTTP

HTTP protocol

Network Services 32

Web and HTTP (hyper-text transfer protocol)

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 (Uniform

Resource Locator) Example URL:

http://www.someschool.edu/someDept/pic.gif

host name path nameprotocol

Network Services 33

HTTP overview

HTTP: hypertext transfer protocol Web’s application layer protocol Stateless 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 2616 (draft in

RFC2068) RFC2617: http authentication

RFC2616 revision started in Oct 06 W3.org/protocols/

PC runningExplorer

Server running

Apache Webserver

Mac runningNavigator

HTTP request

HTTP request

HTTP response

HTTP response

Network Services 34

HTTP overview (continued)

Uses TCP (transport layer protocol):

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 is “stateless” server maintains no

information about past client requests

Protocols that maintain “state” are complex!

past history (state) must be maintained

if server/client crashes, their views of “state” may be inconsistent, must be reconciled

aside

Network Services 35

HTTP connectionsNonpersistent HTTP At most one object is sent over a TCP connection. HTTP/1.0 uses nonpersistent HTTP

Persistent HTTP Multiple objects can be sent over single TCP connection

between client and server. HTTP/1.1 uses persistent connections in default mode Connection established when the 1st web page is

requested and used for all subsequent pages/objects requests until a web server timeout value is reached.

Either the client or server can close the persistent connection by including the connection-token "close" in the Connection-header field of the http request/reply.

Network Services 36

Nonpersistent HTTPSuppose user enters URL www.ece.eng.wayne.edu/home.index

1a. HTTP client initiates TCP connection to HTTP server (process) at www.someSchool.edu on port 80

2. HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object someDepartment/home.index

1b. HTTP server at host www.someSchool.edu waiting for TCP connection at port 80. “accepts” connection, notifying client

3. HTTP server receives request message, forms response message containing requested object, and sends message into its socket

time

(contains text, references to 10

jpeg images)

Network Services 37

Nonpersistent HTTP (cont.)

5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 10 referenced jpeg objects

6. Steps 1-5 repeated for each of 10 jpeg objects

4. HTTP server closes TCP connection.

time

Network Services 38

Response time modeling

Definition of RTT (Round Trip Time): time to send a small packet to travel from client to server and back.

Response time: one RTT to initiate TCP

connection (always needed)

one RTT for HTTP request and first few bytes of HTTP response to return

file transmission timetotal = 2RTT+transmit time (depends

on file size and bandwidth)

time to transmit file

initiate TCPconnection

RTT

requestfile

RTT

filereceived

time time

Network Services 39

Persistent HTTP

Nonpersistent HTTP issues: requires 2 RTTs per object OS overhead for each TCP

connection browsers often open

parallel TCP connections to fetch referenced objects

Persistent HTTP server leaves connection

open after sending response

subsequent HTTP messages between same client/server sent over open connection

Persistent without pipelining: client issues new request

only when previous response has been received

one RTT for each referenced object

Persistent with pipelining: default in HTTP/1.1 client sends requests as

soon as it encounters a referenced object

as little as one RTT for all the referenced objects within the requested web page

Network Services 40

HTTP request message

two types of HTTP messages: request, response

HTTP request message: ASCII (human-readable format)

GET /somedir/page.html HTTP/1.1Host: www.someschool.edu User-agent: Mozilla/4.0Connection: close Accept-language:fr

(extra carriage return, line feed)

request line(GET, POST,

HEAD commands)

header lines

Carriage return, line feed

indicates end of message

Compare toConnection: Keep-Alive

Network Services 41

HTTP request message (RFC 2616): general format

Network Services 42

Uploading form input

Post method: Web page often

includes form input Input is uploaded to

server in entity body

URL method: Uses GET method Input is uploaded in

URL field of request line:

www.somesite.com/animalsearch?monkeys&banana

Network Services 43

Method types

HTTP/1.0 GET POST HEAD

asks server to leave requested object out of response (used mainly for debugging)

HTTP/1.1 GET, POST, HEAD PUT

uploads file in entity body to path specified in URL field

DELETE deletes file specified

in the URL field

Network Services 44

HTTP response message

HTTP/1.1 200 OK Connection: closeDate: 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 ...

status line (protocolstatus code and phrase)

header lines

data, e.g., requested

HTML file

date at web serverwhen file was requested

file last modified date

Network Services 45

HTTP response status codes

200 OK request succeeded, requested object later in this

message

301 Moved Permanently requested object moved, new location specified later

in this message (Location:)

400 Bad Request request message not understood by server

404 Not Found requested document not found on this server

505 HTTP Version Not Supported

In first line in server->client response message.A few sample codes:

Network Services 46

Trying out HTTP (client side) for yourself

1. Telnet to your favorite Web server:

Opens TCP connection to port 80(default HTTP server port) at cis.poly.edu.Anything typed in sent to port 80 at cis.poly.edu

telnet ece.eng.wayne.edu 80

2. Type in a GET HTTP request:

GET /~czxu/test.html HTTP/1.1Host: ece.eng.wayne.edu

By typing this in (hit carriagereturn twice), you sendthis minimal (but complete) GET request to HTTP server

3. Look at response message sent by HTTP server!

Network Services 47

User-server state: cookies

Many major Web sites use cookies: 1) Persistent: file stays on users PC after

closing the browser.2) Non-Persistent (mostly used in J2EE

and .NET platforms): deleted when user closes browser or logs off the web site.

Four components:1) cookie header line of HTTP response

message2) cookie header line in HTTP request

message3) cookie file kept on user’s host,

managed by user’s browser4) back-end database at Web site

Example: Susan access

Internet always from same PC

She visits a specific e-commerce site for first time

When initial HTTP requests arrives at site, site creates a unique ID and creates an entry in backend database for ID

Network Services 48

Cookies: keeping “state” (cont.)

client server

usual http request msg

usual http response +Set-cookie: 1678

usual http request msgcookie: 1678

usual http response msg

usual http request msgcookie: 1678

usual http response msg

cookie-specificaction

cookie-spectificaction

servercreates ID

1678 for user

entry in backend

database

access

acce

ss

Cookie file

amazon: 1678ebay: 8734

Cookie file

ebay: 8734

Cookie file

amazon: 1678ebay: 8734

one week later:

Network Services 49

Cookies (continued)

What cookies can bring:

authorization shopping carts recommendations user session state

(Web e-mail)

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

aside

Network Services 50

Web caches (proxy server)

user sets browser: Web accesses via cache

browser sends all HTTP requests to cache object in cache: cache

returns object else cache requests

object from origin server, then returns object to client

Goal: satisfy client request without involving origin server

client

Proxyserver

client

HTTP request

HTTP request

HTTP response

HTTP response

HTTP request

HTTP response

origin server

origin server

Network Services 51

More about Web caching

Cache acts as both client and server

Typically cache is installed by ISP (university, company, residential ISP)

Why Web caching? Reduce response time for

client request. Reduce traffic and hence

cost on an institution’s internet access link.

Internet dense with caches enables “poor” content providers to effectively deliver content (but so does P2P file sharing)

Network Services 52

HTTP Summary

HTTP request msg format and method types: GET, POST, HEAD, PUT, DELATE

HTTP response msg format and status codes

Cookies and their usage: Persistent vs Non-Persistent cookies

Web cache or proxy server: Conditional GET (If-modified-since:) in HTTP

header

Network Services 53

DNS: Domain Name System

People: many identifiers: SSN, name, passport #

Internet hosts, routers: IP address (32 or 128

bit) - used for addressing datagrams

“canonical name”, e.g., ww.yahoo.com - used by humans

Q: map between IP addresses and name ?

Domain Name System (DNS) is:

1- distributed database implemented in hierarchy of many name servers

2- application-layer protocol: host, routers and name servers communicate to resolve names (address/name translation). DNS protocol uses UDP transport protocol and port 53.

3- employed by other application layer protocols (HTTP, SMTP, FTP) to resolve host names.

Network Services 54

DNS Why not centralize

DNS? single point of

failure traffic volume distant centralized

database maintenance

doesn’t scale!

DNS services Hostname to IP address translation Host aliasing

Canonical (actual) and alias names (user-friendly): cwis-1.wayne.edu for alias www.wayne.edu

Mail server aliasing: mail server and web server can

share the same alias name. E.g. [email protected], wayne.edu

Load distribution Replicated Web servers: a set of IP

addresses for one canonical name. DNS returns the list of IPs for a name but rotated by 1 each time so the user can use the first listed IP.

Network Services 55

Root DNS Servers (13 servers labeled A-M)

com DNS servers org DNS servers edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.comDNS servers

pbs.orgDNS servers

Distributed, Hierarchical Database

Each Client uses a local DNS server that does not belong to the hierarchy:

The local DNS is usually assigned by the DHCP server as part of the temporary IP assignment (run command: “ipconfig /all” to find your local DNS server).

Top-Level Domain Servers (TLDs)

Authoritative DNS servers

Network Services 56

DNS: Root name servers

b USC-ISI Marina del Rey, CAl ICANN Los Angeles, CA

e NASA Mt View, CAf Internet Software C. Palo Alto, CA (and 17 other locations)

i Autonomica, Stockholm (plus 3 other locations)

k RIPE London (also Amsterdam, Frankfurt)

m WIDE Tokyo

a Verisign, Dulles, VAc Cogent, Herndon, VA (also Los Angeles)d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MDj Verisign, ( 11 locations)

There are 13 root DNS server world wide that are labeled A-M: map of root DNS, as of Oct 2006.

Network Services 57

TLD and Authoritative Servers Top-level domain (TLD) servers: responsible for

com, org, net, edu, etc, and all country code top-level domains (ccTLD) us, ca, in, cn, jp. Network solutions maintains servers for com TLD Educause for edu TLD

Authoritative DNS servers: organization’s with public names has 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

Network Services 58

Local Name Server

Does not strictly belong to hierarchy 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.

Network Services 59

requesting hostX

Y

root DNS server

local DNS server

1

23

4

5

6

authoritative DNS server

78

TLD DNS server

Example of Typical DNS request

Client X wants IP address for Y Steps performed:1- Client sends DNS request to the local

DNS server to search on its behalf (recursive query)

2- local DNS contacts one of the root DNSs to resolve hostname Y.

3- root DNS returns the TLD DNS IP to local DNS

4- local DNS contacts one of the TLDs to get an Authoritative DNS nam

5- TLD returns IP of authoritative DNS to local DNS

6- local DNS contacts authoritative DNS to resolve X

7- authoritative DNS returns IP of Y8- local DNS return IP of Y to X

Query 1 is recursiveQueries 2, 4 and 6 are iterative

Example of recursive+iterative DNS query - typically used

Network Services 60

requesting host

requested host

root DNS server

local DNS server

1

2

45

6

authoritative DNS server

7

8

TLD DNS server

3

Recursive and Iterative DNS queries

recursive query: puts burden of name

resolution on contacted name server

heavy load?

iterative query: reply is directly returned

to requesting server “I don’t know this name,

but ask this server”

Example of pure recursive DNS query - not typically used

Network Services 61

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

Client may also cache DNS names update/notify mechanisms under design by

IETF RFC 2136 http://www.ietf.org/html.charters/dnsind-charter.html

Network Services 62

hosts file

local file that is checked by the client DNS of the OS before sending a DNS request. It can speed the web access.

If the requested name is found in the hosts file then its corresponding IP is used.

Can be used to create custom (name-IP) entries. File Location:

windows XP: C:\WINDOWS\system32\drivers\etc most UNIX and Linux: /etc

File Structure: <IP address><space><name><space><# comment> Example of an entry: 127.0.0.1 localhost #default entry

Network Services 63

DNS recordsDNS: distributed db storing resource records (RR)

Type=NS name is domain (e.g. foo.com) value is hostname of authoritative

name server for this domain always in non-authoritative DNSs to

point to authoritative DNSs

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

Type=A name is hostname value is IP address always in authoritative DNS may be cached in non-authoritative

DNSs

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 used by all hosts

Type=MX value is name of mailserver associated

with name that is usually an alias name

company can have a web server and a mail server with the same alias name. e.g. [wayne.edu mail.wayne.edu, MX]

TTL is time to live of the RR and determines when an RR should be removed from cache.

Network Services 64

DNS records with DNS servers

Authoritative DNSs for an institution: must contain Type A RRs for the institution’s public names and IPs. may contain Type MX RRs for the institution’s public mail server

names and IPs. may contain Type CNAME RRs if the institution has Canonical

names for its alias names. TLD DNSs

contain Type NS RRs with each organization’s public name is mapped to its authoritative DNS server names. There is usually a primary and secondary authoritative DNS servers.

contain Type A RRs with the Authoritative DNS server name and IP address.

Network Services 65

DNS protocol, messagesDNS protocol : query and reply messages, both with same message format

msg header identification: 16 bit #, query

and reply msgs use the same #

flags: query or reply 1 bit flag recursion desired or

available 1 bit reply is authoritative

Network Services 66

DNS protocol, messages

Name, type fields for a query

RRs in responseto query

records forauthoritative servers

additional “helpful”info that may be used

Network Services 67

Inserting records into DNS

Example: just created startup “Network Utopia” Register name networkuptopia.com at a registrar

(e.g., Network Solutions) Need to provide registrar with names and IP addresses

of your authoritative name server (primary and secondary)

Registrar inserts two RRs into the com TLD server:

(networkutopia.com, dns1.networkutopia.com, NS)(dns1.networkutopia.com, 212.212.212.1, A)

Put in authoritative server Type A record for www.networkuptopia.com and Type MX record for networkutopia.com

How do people get the IP address of your Web site?

Network Services 68

nslookup command and whois DB used to displays information that you can use to diagnose Domain

Name System (DNS) infrastructure. Contacts the specified DNS server to retrieve requested records.

nslookup <domain or IP to find> <DNS server name> Example: nslookup wayne.com whois database can be used to locate the corresponding registrar,

DNS server and IPs for a particular domain. Only registrars accredited by the Internet Corporation for Assigned

Names and Numbers (ICANN - non-profit org) are authorized to register .aero, .biz, .com, .coop, .info, .museum, .name, .net, .org, or .pro names.

.com whois database: http://www.internic.net/whois.html .edu whois database http://whois.educause.net/index.asp wayne.edu DNS name servers:

NS.WAYNE.EDU 141.217.1.15 NS2.WAYNE.EDU 141.217.1.13 DNS.MERIT.NET NS2.CS.WAYNE.EDU 141.217.16.10

Network Services 69

DNS Vulnerabilities DDoS bw-flooding attack against DNS server.

A large scale attack on 13 DNS root servers on Oct 21, 2002 by using ICMP ping messages

Block ICMP ping packets in packet filtering DNS queries attack

Hard to be filtered Mitigated by caching in local DNS servers

Man-in-the-middle attack Trick a server into bogus records into its cache Hard to implement, because it needs to intercept

packets Reflection attack on other hosts

Send queries with spoofed source addr of a target server

Network Services 70

DNS Summary DNS services:

Hostname to IP address translation Host aliasing, Mail server aliasing, Load distribution

DNS is hierarchical and distributed root DNS vs TLD vs Authoritative DNS vs local DNS recursive vs iterative DNS query DNS cache: local server caches TLDs so that root

servers are rarely visited DNS record types: A, NS, CNAME, MX DNS Query and Reply msg format is the same nslookup command and the whois database DNS vulnerabilities

Network Services 71

Examples of Network Services E-mail Web and DNS Instant messaging Remote login P2P file sharing Multi-user network


video clips



computing

Documents

Network Services1-1 Overview of Internet and Network Services ECE7610/ECE7650