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2004.6.8.

This ClassChapter 9

Next ClassWrap up this semesterDemo/discuss programming assignmentsReview what we have learnedQuestionnaire/FeedbackFinal exam tips

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Applications

DNS SMTP, MIME, IMAP HTTP SNMP RTP SDP, SIP, H.323

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DNS: Domain Name System

People: many identifiers: SSN, name, passport #

Internet hosts, routers: IP address (32 bit) - used

for addressing datagrams

“name”, e.g., gaia.cs.umass.edu - used by humans

Q: map between IP addresses and name ?

Domain Name System: distributed database

implemented in hierarchy of many name servers

application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation) note: core Internet

function, implemented as application-layer protocol

complexity at network’s “edge”

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DNS name servers

no server has all name-to-IP address mappings

local name servers: each ISP, company has

local (default) name server host DNS query first goes

to local name server

authoritative name server: for a host: stores that

host’s IP address, name can perform name/address

translation for that host’s name

Why not centralize DNS? single point of failure traffic volume distant centralized

database maintenance

doesn’t scale!

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DNS: Root name servers

contacted by local name server that can not resolve name root name server:

contacts authoritative name server if name mapping not known

gets mapping returns mapping to local name server

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

e NASA Mt View, CAf Internet Software C. Palo Alto, CA

i NORDUnet Stockholm

k RIPE London

m WIDE Tokyo

a NSI Herndon, VAc PSInet Herndon, VAd U Maryland College Park, MDg DISA Vienna, VAh ARL Aberdeen, MDj NSI (TBD) Herndon, VA

13 root name servers worldwide

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Simple DNS example

host surf.eurecom.fr wants IP address of gaia.cs.umass.edu

1. contacts its local DNS server, dns.eurecom.fr

2. dns.eurecom.fr contacts root name server, if necessary

3. root name server contacts authoritative name server, dns.umass.edu, if necessary requesting host

surf.eurecom.frgaia.cs.umass.edu

root name server

authorititive name serverdns.umass.edu

local name serverdns.eurecom.fr

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DNS example

Root name server: may not know

authoritative name server

may know intermediate name server: who to contact to find authoritative name server

requesting hostsurf.eurecom.fr

gaia.cs.umass.edu

root name server

local name serverdns.eurecom.fr

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authoritative name serverdns.cs.umass.edu

intermediate name serverdns.umass.edu

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DNS: iterated queries

recursive query: puts burden of

name resolution on contacted name server

heavy load?

iterated query: contacted server

replies with name of server to contact

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

requesting hostsurf.eurecom.fr

gaia.cs.umass.edu

root name server

local name serverdns.eurecom.fr

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authoritative name serverdns.cs.umass.edu

intermediate name serverdns.umass.edu

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iterated query

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DNS: caching and updating records

once (any) name server learns mapping, it caches mapping cache entries timeout (disappear)

after some time update/notify mechanisms under

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

charter.html

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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, value, type,ttl)

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 mailserver

associated with name

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DNS protocol, messages

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

msg header identification: 16 bit #

for query, reply to query uses same #

flags: query or reply recursion desired recursion available reply is authoritative

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DNS protocol, messages

Name, type fields for a query

RRs in responseto query

records forauthoritative servers

additional “helpful”info that may be used

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Questions on DNS

Refer to root name server every time you type in an address out of your domain?

TCP or UDP?

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Points of Distinction

Application protocols vs programs Applicaton protocols vs data format SMTP vs ?? HTTP vs ?? SNMP vs ??

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SMTP

HELO cs.princeton.edu250 Hello daemon@mail.cs.princeton.edu [128.12.169.24]

MAIL FROM:<Bob@cs.princeton.edu>250 OK

RCPT TO:<Alice@cisco.com>250 OK

RCPT TO:<Tom@cisco.com>550 No such user here

DATA354 Start mail input; end with <CRLF>.<CRLF> .xxxxxxxxx <CRLF>.<CRLF>250 OK

QUICK221 Closing connection

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HTTP

OperationsOPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, CONNECT

Response Messages1xx - Informational2xx - Success3xx - Redirection4xx - Client error5xx - Server error

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SNMP (I)

Managing entity

Manageddevice

Manageddevice

data

data data

Simple Network Management Protocol

Agent Agent

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SNMP (2)

Evolution of SNMPv1 - Get, GetNext, Setv2 - Get, GetNext, GetBulk, Set, Inform v3 - security and administration capabilitiesLimitations: overhead per MIB, unreliable transfer, CPU overload

Data = MIB (Management Information Base) In Structure of Management Information language

Defines counters at managed device

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RTP

Functionalities common to multimedia applications? interoperate between 2 end hostsdetermine timing relationship in data recover synchronization indicate packet loss indicate frame boundary include user-friendly sender identityefficient use of bandwidth

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Real-time Transport Control Protocol

Main functionsFeedback on application's performanceCorrelate and synchronize different media streams

Convey sender identity for display

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Session/Call Control - SIP

cisco.com proxy

princeton.eduproxy

mypc.cisco.com yourpc.princeton.edu

Sue@cisco.com Meeyoung@princeton.edu

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H.323

ITU recommendation Popular protocol for Internet telephony H.323 terminals talk to each other Or use a H.323 gateway to connect to

PSTN

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Acknowledgments

Some slides are from: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002. All material copyright 1996-2002

J.F Kurose and K.W. Ross, All Rights Reserved