Quality of service, Domain Name system services

QoS & DNS

1. 25.1
QoS,
Application Layer
Paradigms, DNS
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2. QUALITYOFSERVICE
Qualityofservice(QoS)isaninternetworkingissue
thathasbeendiscussedmorethandefined.Wecan
informallydefinequalityofserviceassomethinga
flowseekstoattain.
Topics discussed in this section:
Flow Characteristics Flow Classes
24.23

3. Figure24.15Flowcharacteristics
24.24

4. TECHNIQUES TOIMPROVEQoS
InSection24.5wetriedtodefineQoSintermsofits
characteristics.Inthissection,wediscusssome
techniquesthatcanbeusedtoimprovethequalityof
service.Webrieflydiscussfourcommonmethods:
scheduling,trafficshaping,admissioncontrol,and
resourcereservation.
Topics discussed in this section:
Scheduling Traffic Shaping
Resource Reservation Admission Control
24.25

5. Figure24.16FIFOqueue
24.26

6. Figure24.17Priorityqueuing
24.27

7. Figure24.18Weightedfairqueuing
24.28

8. Figure24.19Leakybucket
24.29

9. Figure24.20Leakybucketimplementation
24.30

10. A leaky bucket algorithm shapes bursty
traffic into fixed-rate traffic by averaging
the data rate. It may drop the packets if
the bucket is full.
Note
24.31

11. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
The token bucket allows bursty traffic at
a regulated maximum rate.
Note
24.32

12. Figure24.21Tokenbucket
24.33

13. INTEGRATEDSERVICES
Twomodelshavebeendesignedtoprovidequalityof
serviceintheInternet:IntegratedServicesand
DifferentiatedServices.Wediscussthefirstmodel
here.
Topics discussed in this section:
Signaling
Flow Specification Admission
Service Classes RSVP
ProblemswithIntegratedServices
24.34

14. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Integrated Services is a flow-based QoS
model designed for IP.
Note
24.35

15. Figure24.22Pathmessages
24.36

16. Figure24.23Resvmessages
24.37

17. Figure24.24Reservationmerging
24.38

18. Figure24.25Reservationstyles
24.39

19. DIFFERENTIATEDSERVICES
DifferentiatedServices(DSorDiffserv)was
introducedbytheIETF(InternetEngineeringTask
Force)tohandletheshortcomingsofIntegrated
Services.
Topicsdiscussed inthissection:
DSField
24.40

20. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Differentiated Services is a class-based
QoS model designed for IP.
Note
24.41

21. Figure24.26DSfield
24.42

22. Figure24.27Traffic
conditioner
24.43

23. 24-9QoSINSWITCHEDNETWORKS
LetusnowdiscussQoSasusedintwoswitched
networks:FrameRelayandATM.Thesetwonetworks
arevirtual-circuitnetworksthatneedasignaling
protocolsuchasRSVP.
Topics discussed in this section:
QoS in Frame Relay QoS in ATM
24.44

24. Figure24.28Relationshipbetweentrafficcontrolattributes
24.45

25. Figure24.29Userrate inrelationtoBcandBc +Be
24.46

26. Figure24.30Service
classes
24.47

27. Relationshipofserviceclasses tothetotalcapacityof thenetwork
24.48

28. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
ApplicationLayer
•Theapplicationlayerprovidesservicestotheuser.
•Communicationisprovidedusingalogicalconnection,which
meansthatthetwoapplicationlayersassumethatthereisan
imaginarydirectconnectionthroughwhichtheycansendand
receivethemessages.
•ApplicationLayerprovidesafacilitybywhichuserscanforward
severalemailsanditalsoprovidesastoragefacility.
•Thislayerallowsuserstoaccess,retrieveandmanagefilesina
remotecomputer.
•Itallowsuserstologonasaremotehost.
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29. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
ProvidingServices
•TheInternetwasoriginallydesignedforthesamepurpose:toprovideservice
tousersaroundtheworld.
•Newprotocolscanbeaddedorsomeprotocolscanberemovedorreplaced
bytheInternetauthorities.
•Sincetheapplicationlayeristheonlylayerthatprovidesservicestothe
Internetuser,itallowsnewapplicationprotocolstobeeasilyaddedtothe
Internet.
StandardApplication-LayerProtocols
•Thereareseveralapplication-layerprotocolsthathavebeenstandardizedand
documentedbytheInternetauthority.
•Eachstandardprotocolisapairofcomputerprogramsthatinteractwiththe
userandthetransportlayertoprovideaspecificservicetotheuser.
•Ex:Telnet,FTP,TFTP,SMTP,SNMP,DNS,DHCP.
NonstandardApplication-LayerProtocols
•Aprogrammercancreateanonstandardapplication-layerprogram.
•Itisthecreationofanonstandard(proprietary)protocol,whichdoesnoteven
needtheapprovaloftheInternetauthoritiesifprivatelyused.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 29

30. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Application-Layer Paradigms
TwoparadigmshavebeendevelopedduringthelifetimeoftheInternet:
1.theclient-serverparadigm
2.thepeer-to-peerparadigm.
TraditionalParadigm:Client-Server
•Thetraditionalparadigmiscalledtheclient-serverparadigm.
•Serviceproviderisanapplicationprogram,calledtheserverprocess;itrunscontinuously,waiting
foranotherapplicationprogram,calledtheclientprocess,tomakeaconnectionthroughthe
Internetandaskforservice.
•Theserverprocessmustberunningallthetime;theclientprocessisstartedwhentheclient
needstoreceiveservice.
•Severaltraditionalservicesarestillusingthisparadigm,includingtheWorldWideWeb(WWW)
anditsvehicleHyperTextTransferProtocol(HTTP),filetransferproto-col(FTP),secureshell(SSH),
e-mail,andsoon.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 30
Figure25.2Exampleofaclient-
serverparadigm

31. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Peer-to-Peer
•Anewparadigm,calledthepeer-to-peerparadigm(P2Pparadigm)hasemergedto
respondtotheneedsofsomenewapplications.
•Inthisparadigm,thereisnoneedforaserverprocesstoberunningallthetimeand
waitingfortheclientprocessestoconnect.
•Theresponsibilityissharedbetweenpeers.
•AcomputerconnectedtotheInternetcanprovideserviceatonetimeandreceive
serviceatanothertime.
•Acomputercanevenprovideandreceiveservicesatthesametime.
•Therearesomenewapplications,suchasBitTorrent,Skype,IPTV,andInternet
telephony.
5/14/2024 Dr. Shivashankar, E&CE, RRIT 31
Figure25.3Exampleofapeer-
to-peerparadigm

32. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Mixed Paradigm
•Anapplicationmaychoosetouseamixtureofthetwo
paradigmsbycombiningtheadvantagesofboth.
•Forexample,alight-loadclient-servercommunicationcanbe
usedtofindtheaddressofthepeerthatcanofferaservice.
•Whentheaddressofthepeerisfound,theactualservicecanbe
receivedfromthepeerbyusingthepeer-to-peerparadigm.
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33. 25.33
Figure 25.1 Example of using the DNS service
server
Typo in textbook

34. 25.34
25-1 NAME SPACE
Tobeunambiguous,thenamesassignedtomachines
mustbecarefullyselectedfromanamespacewith
completecontroloverthebindingbetweenthenames
andIPaddresses.
Flat Name Space: hard to manage for large-scale system
Hierarchical Name Space: name has several parts
Topics discussed in this section:

35. 25.35
25-2 DOMAIN NAME SPACE
Tohaveahierarchicalnamespace,adomainname
spacewasdesigned.Inthisdesignthenamesare
definedinaninverted-treestructurewiththerootat
thetop.Thetreecanhaveonly128levels:level0
(root)tolevel127.
Label
Domain Name
Domain
Topics discussed in this section:

36. 25.36
Figure 25.2 Domain name space
root

37. 25.37
Figure 25.3 Domain names and labels

38. 25.38
Figure 25.5 Domains: subtree of the domain name space

39. 25.39
25-3 DISTRIBUTION OF NAME SPACE
Theinformationcontainedinthedomainnamespace
mustbestored.However,itisveryinefficientandalso
unreliabletohavejustonecomputerstoresuchahuge
amountofinformation.Inthissection,wediscussthe
distributionofthedomainnamespace.
Hierarchy of Name Servers
Zone
Root Server
Primary and Secondary Servers
Topics discussed in this section:

40. 25.40
Figure 25.6 Hierarchy of name servers

41. DNS: Root name servers
b USC-ISI Marina del Rey, CA
l ICANN Los Angeles, CA
e NASA Mt View, CA
f Internet Software C. PaloAlto, CA
(and 17 other locations)
i Autonomica, Stockholm (plus 3 other
locations)
k RIPE London (also Amsterdam, Frankfurt)
m WIDE Tokyo
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)
13 root name
servers
worldwide

42. TLD and Authoritative Servers
Top-level domain (TLD) servers:responsible for
com, org, net, edu, etc, and all top-level country
domains uk, fr, ca, jp.
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 (paid by the organization)

43. 25.43
Figure 25.7 Zones and domains

44. 25.44
Two types of DNS server: A primary server
loads all information from the disk file; the
secondary server loads all information from
the primary server. Reason: redundancy
When the secondary downloads
information from the primary, it is called zone
transfer.
Note

45. 25.45
25-4 DNS IN THE INTERNET
DNSisaprotocolthatcanbeusedindifferent
platforms.IntheInternet,thedomainnamespace
(tree)isdividedintothreedifferentsections:generic
domains,countrydomains,andtheinversedomain.
Generic Domains
Country Domains
Inverse Domain
Topics discussed in this section:

46. 25.46
Unix: nslookup, dig
Windows: nslookup
DNS Query Commands

47. 25.47
Figure 25.8 DNS IN THE INTERNET

48. 25.48
Figure 25.9 Generic domains

49. 25.49
Table 25.1 Generic domain labels

50. 25.50
Figure 25.10 Country domains

51. 25.51
25-5 RESOLUTION
Mappinganametoanaddressoranaddresstoa
nameiscalledname-addressresolution.
Resolver
Mapping Names to Addresses
Mapping Addresses to Names
Recursive Resolution
Caching
Topics discussed in this section:

52. 25.52
Figure 25.12 Recursive resolution

53. 25.53
Figure 25.13 Iterative resolution

54. 25.54
Caching: Main Reason for the Efficiency of DNS
All DNS servers cache prior query results
Normal DNS query will not go through the
full steps of recursive/iterative resolution

55. 25.55
25-6 DNS MESSAGES
DNShastwotypesofmessages:queryandresponse.
Bothtypeshavethesameformat.Thequerymessage
consistsofaheaderandquestionrecords;the
responsemessageconsistsofaheader,question
records,answerrecords,authoritativerecords,and
additionalrecords.
Header
Topics discussed in this section:

56. 25.56
Figure 25.14 Query and response messages

57. 25.57
Figure 25.15 Header format

58. 25.58
25-7 TYPES OF RECORDS
AswesawinSection25.6,twotypesofrecordsare
usedinDNS.Thequestionrecordsareusedinthe
questionsectionofthequeryandresponsemessages.
Theresourcerecordsareusedintheanswer,
authoritative,andadditionalinformationsectionsof
theresponsemessage.
Question Record
Resource Record
Topics discussed in this section:

59. DNS records
DNS:distributed db storing Resource Records (RR)
Type=NS
nameis domain (e.g.
foo.com)
valueis name of
authoritative DNS server
for this domain
RR format: (name, value, type, ttl)
Type=A
nameis hostname
valueis IP address
Type=CNAME
nameis alias name for some
“canonical” (the real) name
www.ibm.com is really
servereast.backup2.ibm.com
valueis canonical name
Type=MX
valueis name of mailserver
associated with name
25.59

60. DNS protocol, messages
DNS protocol :queryand replymessages, 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
25.60

61. DNS protocol, messages (UDP 53)
Name, type fields
for a query
RRs in
response
to query
records for
authoritative servers
additional “helpful”
info that may be used
Let’s check a web example using Wireshark!
(MX record: nslookup –type=MX cs.ucf.edu or
dig mx cs.ucf.edu)
25.61

62. Inserting records into DNS
Example: just created startup “netwar”
Register name netwar.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:
(netwar.com, dns1.netwar.com, NS)
(dns1.netwar.com, 212.212.212.1, A)
Put in authoritative server dns1.netwar.com
Type A record for www.netwar.com
Type CName for netwar.com (alias)
Type MX record for netwar.com (email)
Type A record for the email server
How do people get the IP address of your Web site?
25.62

63. 25.63
DNS can use the services of UDP or TCP
using the well-known port 53.
Note