12-DNSWeb - 1 DNS and the Web EE122 Fall 2011 Scott Shenker

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Unformatted text preview: 1 DNS and the Web EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley Announcements Midterm on Monday Closed book Crib sheet: 2-sided, 10pt font minimum. o This is to keep you from wasting your time! Midterm will cover todays lecture Review on Wednesday No office hours this week But available today, Wednesday, Thursday afternoon 2 3 DNS Naming Internet has one global system of addressing: IP By explicit design And one global system of naming: DNS Almost by accident At the time, only items worth naming were hosts A mistake that causes many painful workarounds Everything is now named relative to a host Content is most notable example (URL structure) 4 Logical Steps in Using Internet Human has name of entity she wants to access Content, host, etc. Invokes an application to perform relevant task Using that name App invokes DNS to translate name to address App invokes transport protocol to contact host Using address as destination 5 Addresses vs Names Scope of relevance: App/user is primarily concerned with names Network is primarily concerned with addresses Timescales: Name lookup once (or get from cache) Address lookup on each packet When moving a host to a different subnet: The address changes The name does not change When moving content to a differently named host Name and address both change! 6 7 Relationship Betwn Names/Addresses Addresses can change underneath Move www.cnn.com to 4.125.91.21 Humans/Apps should be unaffected Name could map to multiple IP addresses www.cnn.com to multiple replicas of the Web site Enables o Load-balancing o Reducing latency by picking nearby servers Multiple names for the same address E.g., aliases like www.cnn.com and cnn.com Mnemonic stable name, and dynamic canonical name o Canonical name = actual name of host Mapping from Names to Addresses Originally: per-host file /etc/hosts SRI (Menlo Park) kept master copy Downloaded regularly Flat namespace Single server not resilient, doesnt scale Adopted a distributed hierarchical system Two intertwined hierarchies: Infrastructure: hierarchy of DNS servers Naming structure: www.cnn.com 8 9 Domain Name System (DNS) Top of hierarchy: Root Location hardwired into other servers Next Level: Top-level domain (TLD) servers .com, .edu, etc. Managed professionally Bottom Level: Authoritative DNS servers Actually do the mapping Can be maintained locally or by a service provider 10 Distributed Hierarchical Database com edu org ac uk zw arpa unnamed root bar west east foo my ac cam usr in- addr generic domains country domains my.east.bar.edu usr.cam.ac.uk Top-Level Domains (TLDs) 11 DNS Root Located in Virginia, USA How do we make the root scale?...
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This note was uploaded on 01/09/2012 for the course ELECTRICAL 122 taught by Professor Shenker during the Spring '11 term at University of California, Berkeley.

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12-DNSWeb - 1 DNS and the Web EE122 Fall 2011 Scott Shenker

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