Todays Objec2ves Naming Challenges Domain Name System Oct 9, 2017 - - PDF document

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Today’s Objec2ves

• Naming Challenges
• Domain Name System

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Review

• What is RPC?

Ø What is its purpose? Ø How does it work? Ø What implementa2on of RPC are we using in Project 2?

• What is RMI? How does it relate to RPC?

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Terminology

• Pure names - uninterpreted bit paSerns; must be “looked up”

before they are used

Ø Example: Mac address

• Non-pure names - contain informa2on about the object they

name (such as loca2on or address); inadequate for object iden2fica2on over 2me

Ø Example: IP address

• Resolu2on - translate a name into useful data about an object
• Binding - associa2on between name and object
• ASribute - value of a property associated with an object (names

are o`en bound to aSributes)

• Contexts - sets of bindings between names and aSributes for
• bjects

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Naming Services Design Goals

• Handle an arbitrary number of names
• Have a long (infinite?) life2me
• Provide high availability
• Hide (or isolate) faults
• Tolerate mistrust

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Types of Naming Systems

• Flat
• Structured
• ASribute-based

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Flat Systems

• Tend to be for LAN
• No loca2on or other informa2on
• Example: RPC or RMI naming

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DOMAIN NAME SYSTEM

Structured naming

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DNS Components

• A globally distributed, scalable, reliable database
• Name Space:

Ø Specifica2ons for a structured name space and data associated with the names

• Resolvers:

Ø Client programs that extract informa2on from Name Servers.

• Name Servers:

Ø Server programs which hold informa2on about the structure and the names.

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Name Space

9

""

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root What are subdomains of wlu.edu?

Global Distribu2on

• Data is maintained locally, but retrievable

globally

Ø No single computer has all DNS data

• DNS lookups can be performed by any device
• Remote DNS data is locally cachable to improve

performance

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Scalability

• No limit to the size of the database
• No limit to the number of queries

Ø Tens of thousands of queries handled easily every second

• Queries distributed among primaries,

secondaries, and caches

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Reliability

• Data is replicated

Ø Data from primary is copied to mul2ple secondaries

• Clients can query

Ø Primary server Ø Any of the copies at secondary servers

• Clients will typically query local caches
• DNS protocols can use either UDP or TCP

Ø If UDP, DNS protocol handles retransmission, sequencing, etc.

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Dynamicity

• Primary database can be updated dynamically

Ø Add/delete/modify of any record

• Modifica2on of the primary database triggers

replica2on

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Resolvers

• Resolver maps a name to an address and vice

versa.

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Query Response Resolver Name Server

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Itera2ve Resolu2on: Referrals

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itera2ve response (referral) “I don't know. Try a3.nstld.com.” 2

a3.nstld .com

3

client

itera2ve request “What is the IP address of www.google.com?”

wlu server

1 itera2ve response (referral) “I don't know. Try a.root- servers.net.” 4

a.root server

5 itera2ve response (referral) “I don't know. Try a.gtld-servers.net.” 6

a.gtld-

server

7 itera2ve response (referral) “I don't know. Try ns1.google.com.” 8

ns1.google .com

9 itera2ve response “The IP address of www.google.com is 173.194.175.103.” 10

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Recursive Resolu2on

16

client

recursive request “What is the IP address of www.google.com?” wlu server 1 edu server 2 root server 3 com

server

4 google server 5 recursive response “The IP address of www.google.com is 216.239.37.99.” 6 10 7 8 9

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Name Server: Architecture

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Primary server Zone transfer Zone data file From disk

Authoritative Data primary and secondary zones Agent looks up queries

• n behalf of resolvers

Cache Data responses from

• ther name servers

Name Server Process

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Name Server: Authorita2ve Data

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Resolver Query Response

Authoritative Data primary and secondary zones Agent looks up queries

• n behalf of resolvers

Cache Data responses from

• ther name servers

Name Server Process

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Name Server: Using Other Name Servers

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Arbitrary name server Response Resolver Query Query

Authoritative Data Primary and Secondary zones Agent looks up queries

• n behalf of resolvers

Cache Data responses from

• ther name servers

Name Server Process

Response

Name Server: Cached Data

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Query Response

Authoritative Data Primary and Secondary zones Agent looks up queries

• n behalf of resolvers

Cache Data responses from

• ther name servers

Name Server Process

Resolver

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Block Diagram

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User Program Foreign Name Server Cache Resolver

Query Query

Reference Response Addition Response

Dynamic DNS

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Client DHCP Server Primary DNS Server Zone File IP Address? IP Address Update

Dynamic Host Configuration Protocol

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Looking Ahead

• COD paper – due tonight
• Preliminary Bookstore deadline next Monday

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