Simulation of DNS(Domain Name System) Using SimLib

Simulation of DNS(Domain Name System)Using SimLibSubmitted byPrem TamangSubmitted toDr. Lawrence J. Osborne

Table of Contents1. Introduction ……………………………………………………………… 32. Motivation and Challenges………………………………………………. 53. Assumptions ……………………………………………………………… 54. Implementations ………………………………………………………….. 7• Event Graph• Selection of Input Probability Distribution for the Randomvariables existing in the Modeli) Assessment of Sample Independenceii) Hypothesizing Families of Distributionsiii) Estimation of Parametersiv) Determining How Representative the Fitted Distribution arev) Goodness-of Fits Tests5. Simulation Results ………………………………………………………………… 126. Analysis of results………………………………………………………………… 177. References………..………………………………………………………………… 18

1. IntroductionThe Domain Name System (DNS) is a distributed database that allows local control ofthe segments of the overall database, yet data in each segment are available across the entirenetwork through a client-server scheme. This hierarchical naming system contains programscalled name servers which stores information about some segment of the database and make itavailable to clients, called resolvers. Resolvers are often just library routines that create queriesand send them across a network to a name server.This project simulates the behavior of the name servers which resolves domain namesmeaningful to humans into the numerical (binary) identifiers associated with networkingequipment for the purpose of locating and addressing these devices worldwide.Client1Client2Client3Client4Client5NS Queuries[e.g.google.com]QUEUENS Queuries[e.g.google.com]NameServer1NameServer 2Reply[COM:IP Address]RootGeneral Top Level DomaimCOMName ServersEDUMicrosoft.com 202.46.197.32Novell.com 130.57.5.30Google.com 74.125.157.147Query Resolved[e.g.google.com : 74.125.157.147]Model of the Simulation SystemLamar.edu 148.158.64.247Tamu.edu 165.91.22.88Gatech.edu 130.207.244.244This simulation system consists of the name servers that receive requests one at a time from theset of clients within its network in a continuous manner. Name servers are present in three levels,the root level, the top level domains and the respective authoritive name servers. Name Servers

supports Iterative Queries or Non-Recursive Queries i.e. the requester must be capable ofpursuing referrals. The requests from the clients are queued in the name server if the name serveris busy in processing the packet. Once the request packet is processed, the query will passed tothe Root level Domain which contains information regarding all the top level domains like com ,edu , info etc. Then the root level domain refers the respective top level domain (i.e. provides theIP Address) to the names server .The request will again be queued in the name server since thepackets needs to be processed. The request will be redirected to the top level domains whichagain sends the referrals(IP Address) of the respective Name Server. Finally the respectiveAuthoritive name servers provides the IP Address for the given domain name back and theresponse will be forwarded back to the Client.e.g. Client 1 sends the request www.google.com , to the NameServer1. There exist equal chancesof selection of the NameServers based on the equal probability. If NS1 is busy processing thepacket, it will be stored into the queue. Then the reqest is forwarded to the Root Level Domain[XX.XX.XX.XX]. It replies back with the IP Address of the Top Level Domains - COM. Therequest are again queued on the NS1 server. Once its turns comes, again the request will beforwarded for resolving to the COM Top Level Domain. The COM Top level domains againreplies back with the IPAddress of the NameServer of Google.com. The request is againprocessed at NS1 and the redirected to the NameServer of the Google. Finally the AuthoritiveNameServer of google.com provides the IP Address of the WebServer in the DNS Reply to theNS1. The NS1 then replies back to the client with the valid IP Address of the requested domainwww.google.com.

2. Motivation and ChallengesIn the internet, DNS is one of the mostly used systems since for accessing any resourceon the internet, it requires the IP Address of that resource and DNS provides this. Every networkconsists of at least one DNS Server. The performance of the network is heavily dependent uponthe Name Servers. So it’s always important to know how well the DNS performs in the network.Various factors like the total number of queries, type of queries, the response time, and numbersof available master DNS Servers affects the performance of DNS Servers. So this projectprovides the simulation model of the DNS system to measure the arrival rate of the DNS queries,response time of the Queries , handling of various types of valid and invalid queries and loadbalancing depending upon the numbers of DNS Servers etc.The biggest challenge in this project was hypothesizing the probability distribution forthe random variable like Inter-arrival Time of DNS Queries, Service type for the packetprocessing, Round Trip time to the Domain Name Servers. Also, designing the work-flow modelfor representing the name servers and various zones was quite difficult.3. Assumptions:• The system consist of basic components only i.e. Client Machines, Name Servers . Thezone contains three levels, Root zone, general Top Level Domain(gTLD) and theauthoritive name servers. Currently the system implements only two types of gTLD ,COM and EDU. Each gTLD at least contains the name server information of 5authoritive name servers.• NameServer supports only Iterative Queries and doesn’t provide the caching.• Interarrival time of the DNS Queries are IID and arrives the system one at a time.• Data for estimating the Mean Value for Interarrival time has been obtained from theinternet sites [2][3]. .• The servers takes time ( though very less) for the packet processing and if the server isbusy processing the packet, the request from the client as well as the responses from theother root, gTLD and authoritive name servers has to wait in queue.

• Response time i.e. the total time when the client gets back the response for this DNSQueries is dependent upon the Service Time or Packet Processing Time of the DNSServer, Round Trip Time from the DNS Server to the zone servers.• The simulation is performed for length of 5 hrs.List Specifications:The simulation model measure the performance of the DNS on the basis of followingmeasures :• Average Response Time of the System• Average Delay in the Queue• Time Average No. of the Request and Responses in the Queue• Utilization of the Name Servers• Efficiency of the system depending upon the various numbers of name servers• Proportion of the DNS Queries for Invalid Domains• Proportion of the NDS Queries for COM and EDU Domains.

4. Implementation :This project uses the C programming language and SIMLIB package for simulation.ArrivalDepartureEndSimulationEvent Graph for DNS System Model.Selection of Input Probability Distribution :This simulation model basically consists of three Random Variables.i) Inter-arrival Timeii) Service Timeiii)Round Trip TimeAll the random variables are Identical- Independent Distribution. This project uses the standardtechniques of statistical inference to “fit” a theoretical distribution form to the data and toperform hypothesis tests to determine the goodness of fit. The following steps are performed onthe collected data by the help of Expertfit Software from Averill M.Law & Associates to selectthe Input Probability Distribution:

Data Summary from Expertfit Software.i) Inter-arrival Time :Hypothesized Probability Distribution : Weibull Probability Distributiona) Assessment of Sample Independence• Scatter Diagram :• Lag-Correlation Plot:

) Hypothesizing Families of Distributions:Histograms:c) Estimation of Parameters :The probability distribution hypothesized appears to be “Gamma” distribution which belongs tothe Heavy Tailed Distribution Family.Estimated Parameters :

Alpha = Shape Parameter = 62.19625Beta = Scale Parameter = 0.80464d) Determining How Representative the Fitted Distribution are :• Density-Histogram Plots :• Distribution-Function-Differences Plots :e) Goodness-of Fits Tests :H 0 : The X i ’s are IID random variables with Weibull Probability Distribution function

• Chi-Square Tests :• Kolmogorov-Smirnov Tests :Thus the null Hypothesis H 0 cannot be rejected.The random variates in this simulation model are generated from the probability distribution ,Weibull, using the following formula.X=B(-1n U) 1/αwhere U ~ U(0,1)

ii) Service Time or Packet Processing Time :Actual sets of data could not be achieved. However based on the interpreted data on site [4]the value considered for service time is 600-800 microseconds . So a uniform distributionU(0.0006-0.0008) is used to generate the Random Variates.iii) Round Trip Time :Actual sets of data could not be achieved. However, the gTLD Server [5] shows that the RTTtime varies about 200-400 ms.So a uniform distribution is considered U(0.2-0.4) to generate the Radom Variates.5. Simulation Results:The simulation is performed with the varying numbers of clients and servers.When the numbers of Servers = 2 and No. of Clients machines is varied from 5to 15DNS Server Simulation=====================Total Number of Server : 2Number of Client Machines : 5 to 15 by 10Shape Parameter(Alpha) for Weibull Distribution of Interarrival Time :62.19625 secondsScale Parameter(Beta) for Weibull Distribution of Interarrival Time :0.80464 secondsLower Limit for Uniform Distribution of Service Time :Upper Limit for Uniform Distribution of Service Time :Lower Limit for Uniform Distribution of Round Trip Time :Upper Limit for Uniform Distribution of Round Trip Time :Total Time for Simulation : 1.000 minutes0.00060 seconds0.00080 seconds0.20000 seconds0.40000 secondsNo. of Clients : 5Proportion of DNS Queries Related to COM Domain : (183/564) : 0.324468Proportion of DNS Queries Related to EDU Domain : (192/564) : 0.340426Proportion of Invalid Queries : (189/564) : 0.335106Response Times for Client Machines===================================

sampstNumbervariableofnumber Average values Maximum Minimum________________________________________________________________________1 27.1045 37.0000 58.9534 0.7240052 28.4987 40.0000 57.5436 1.023453 31.3211 32.0000 58.2869 2.486364 35.1893 35.0000 58.7487 3.303195 32.5062 37.0000 59.0197 0.879908________________________________________________________________________CPU Utilization=================File Timenumber average Maximum Minimum_______________________________________________________3 0.00713647 1.00000 0.000004 0.00799003 1.00000 0.00000______________________________________________________Time Average Number of Delay for Requests and Responses in Queue=================File Timenumber average Maximum Minimum_______________________________________________________1 3.21706E-05 1.00000 0.000002 4.27246E-05 1.00000 0.00000_______________________________________________________No. of Clients : 15Proportion of DNS Queries Related to COM Domain : (557/1676) : 0.332339Proportion of DNS Queries Related to EDU Domain : (565/1676) : 0.337112Proportion of Invalid Queries : (554/1676) :0.330549Response Times for Client Machines===================================sampstNumbervariableofnumber Average values Maximum Minimum________________________________________________________________________1 32.3719 39.0000 56.8068 1.770292 30.2344 40.0000 59.1481 0.9150143 30.3714 47.0000 57.6046 0.9317484 28.1619 38.0000 59.1190 1.759095 33.1265 35.0000 59.0617 0.9252816 30.0880 34.0000 57.3162 1.785007 28.4804 29.0000 57.3242 4.881228 30.5127 42.0000 59.1637 0.9041729 29.7878 38.0000 58.2726 0.995557

10 35.5800 39.0000 58.7033 1.7894811 28.2283 35.0000 58.5564 0.87873512 31.8850 30.0000 57.2434 4.1196513 30.6599 37.0000 56.7885 0.94760414 31.6593 37.0000 57.3897 5.6423615 29.6046 35.0000 59.0936 1.58028________________________________________________________________________CPU Utilization=================File Timenumber average Maximum Minimum_______________________________________________________3 0.0226064 1.00000 0.000004 0.0227799 1.00000 0.00000_______________________________________________________Time Average Number of Delay for Requests and Responses in Queue=================File Timenumber average Maximum Minimum_______________________________________________________1 0.000317542 2.00000 0.000002 0.000275157 1.00000 0.00000______________________________________________________When the numbers of Servers = 5 and No. of Clients machines is varied from 5to 15DNS Server Simulation=====================Total Number of Server : 5Number of Client Machines : 5 to 15 by 10Shape Parameter(Alpha) for Weibull Distribution of Interarrival Time : 62.19625 secondsScale Parameter(Beta) for Weibull Distribution of Interarrival Time : 0.80464 secondsLower Limit for Uniform Distribution of Service Time : 0.00060 secondsUpper Limit for Uniform Distribution of Service Time : 0.00080 secondsLower Limit for Uniform Distribution of Round Trip Time : 0.20000 secondsUpper Limit for Uniform Distribution of Round Trip Time : 0.40000 secondsTotal Time for Simulation : 1.000 minutesNo. of Clients : 5Proportion of DNS Queries Related to COM Domain : (183/564) : 0.324468Proportion of DNS Queries Related to EDU Domain : (192/564) : 0.340426Proportion of Invalid Queries : (189/564) : 0.335106Response Times for Client Machines===================================sampstNumbervariableof

number Average values Maximum Minimum________________________________________________________________________1 27.1143 37.0000 59.0959 0.7240052 28.5071 40.0000 57.5436 1.023453 31.3350 32.0000 58.5059 2.486364 35.1981 35.0000 58.9449 3.303195 32.4927 37.0000 58.9607 0.879908_______________________________________________________________________CPU Utilization=================File Timenumber average Maximum Minimum_______________________________________________________6 0.00284082 1.00000 0.000007 0.00285162 1.00000 0.000008 0.00291142 1.00000 0.000009 0.00318045 1.00000 0.0000010 0.00333871 1.00000 0.00000_______________________________________________________Time Average Number of Delay for Requests and Responses in Queue======================================================File Timenumber average Maximum Minimum_______________________________________________________1 0.00000 -1.00000E+30 1.00000E+302 0.00000 -1.00000E+30 1.00000E+303 0.00000 -1.00000E+30 1.00000E+304 6.42141E-06 1.00000 0.000005 0.00000 -1.00000E+30 1.00000E+30_______________________________________________________No. of Clients : 5Proportion of DNS Queries Related to COM Domain : (557/1676) : 0.332339Proportion of DNS Queries Related to EDU Domain : (565/1676) : 0.337112Proportion of Invalid Queries : (554/1676) : 0.330549Response Times for Client Machines============================sampstNumbervariableofnumber Average values Maximum Minimum________________________________________________________________________1 32.3825 39.0000 57.0152 1.786482 30.2167 40.0000 59.1481 0.9150143 30.3564 47.0000 57.6517 0.9317484 27.3149 37.0000 57.5751 1.562595 33.1145 35.0000 59.0618 0.925281

6 30.0895 34.0000 57.3960 1.688707 28.4713 29.0000 57.1220 4.935718 29.8303 41.0000 58.6793 0.9041729 29.8014 38.0000 58.2613 0.99555710 35.5758 39.0000 58.5802 1.8610311 28.2035 35.0000 58.6058 0.87873512 31.8920 30.0000 57.2678 4.0415413 30.6812 37.0000 56.6761 0.94760414 31.6435 37.0000 57.4134 5.6417515 29.6031 35.0000 59.0294 1.58028________________________________________________________________________CPU Utilization============File Timenumber average Maximum Minimum_______________________________________________________6 0.00843381 1.00000 0.000007 0.00975168 1.00000 0.000008 0.00865565 1.00000 0.000009 0.00976150 1.00000 0.0000010 0.00880374 1.00000 0.00000______________________________________________________Time Average Number of Delay for Requests and Responses in Queue======================================================File Timenumber average Maximum Minimum_______________________________________________________1 4.15603E-05 1.00000 0.000002 1.49131E-05 1.00000 0.000003 2.98977E-05 1.00000 0.000004 6.61135E-05 1.00000 0.000005 7.05481E-05 1.00000 0.00000_______________________________________________________

6. Analysis of ResultsThe results from the simulation model are obtained as expected. As we can seethat, keeping the number of servers constant (i.e. 2) in first case, when the no. of clients areincreased from 5 to 15 , CPU Utilization as well as the time average no. delay of requests andresponses in the Queue are also increased. As we can see the packet processing time by theName Server in comparison to the Round Trip Time, is very small, so we don’t have manypackets in the queue which also explains the low utilization value of CPU. Server simplyprocesses the packets and redirects it to the other Domain Servers.Similarly, when the numbers of name servers are increased the load is dividedresulting into low CPU Utilization as well as low value of time average no. of delay of requestsand responses in the Queue.Due to the lack of the output data from the real system , the output of thissimulation could not be validated to the full extend. However, regarding the Interarrival time ,100 samples of data were taken from simulation and fed into the Expertfit Software , whichconfirms the Weibull Distribution of the Interarrival time.Further the Confidence-Interval Approach Based could have been applied forstatistical comparison of the real system observed data and simulation output data.

References:1) Jaeyeon Jung, Emil Sit, Hari Balakrishnan, Reobert Morris ,DNS performance and theeffectiveness of caching. IEEE/ACM Transactions on Networking (TON ) , pages , 589-603 ,20022) http://ita.ee.lbl.gov/html/contrib/DEC-PKT.html3) http://mawi.wide.ad.jp/mawi/dnsprobe/results/4) http://doolittle.icarus.com/ntpclient/README5)http://www.caida.org/cgibin/dns_perf/main.pl?metric=rtt&class=root&class=gTLD&site=ua&s-y=2010&s-m=7&sd=7&interval=1&type=Plot+&.cgifields=site&.cgifields=metric&.cgifields=class