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588 Section 7

588 Section 7. Neil Spring May 18, 1999. Schedule. Homework 2 review DNS Active Naming. Reminders & Notes. Programming Assignment 2 due May 24 Homework 3 will be due June 1 Project 3 will be due June 7 Time to talk to Tom about the final project. Homework 2 -1.

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588 Section 7

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  1. 588 Section 7 Neil Spring May 18, 1999

  2. Schedule • Homework 2 review • DNS • Active Naming

  3. Reminders & Notes • Programming Assignment 2 due May 24 • Homework 3 will be due June 1 • Project 3 will be due June 7 • Time to talk to Tom about the final project

  4. Homework 2 -1 • A forwarding packets through C? • whenever cost of A-B is higher than A-C-B • Asymmetric cost info • link state - everyone will get consistent • distance vector - asymmetric routes • Link inconsistency affecting routes • if it’s in the middle of the network

  5. Homework 2 - 2 • Number the leaves 0..n • The route to 010 is (from the root): left right left. • The route from 001 to 010 is: • up (to the 00? router) • up (to the 0?? router) • right (to the 01? Router) • left (to the 010 host)

  6. Homework 2 - 3 • Key realizations: • Hierarchical routing • end nodes are dumb • routers know the topology • Loose source routing • end nodes know the topology • routers don’t know much • router failure is less transparent

  7. 2 - 4 • In slow start, each ack increases cwnd by one. • Delayed acks not really shown here.

  8. Homework 2 - 5 • I don’t know yet. :)

  9. All you need to know about DNS • Host to IP address mapping • poplar.cs.washington.edu = 128.95.2.24 • IP address to host mapping • 24.2.95.128.in-addr.arpa = poplar… • Caching • updates aren’t immediately visible • negative caching important too • UDP

  10. All you might want to know • Variable depth hierarchy • .edu • .washington.edu • .cs.washington.edu • .porcupine.cs.washington.edu • Protection against bad data • TTL/data value reversal example • Caching doesn’t extend to hosts • To speed things up?

  11. DNS Attributes • A: IP Address • ip from name • CNAME: Canonical name • name to other name • NS: Authoritative Name Server • PTR: Pointer record • name from ip • MX: Mail Exchange • gets mail destined for this machine

  12. How to get em (host) • host poplar: • poplar.cs.washington.edu A 128.95.2.24 • host -t CNAME poplar • poplar.cs.washington.edu has no CNAME record (Authoritative answer) • host -t CNAME www.cs.washington.edu • www.cs.washington.edu CNAME bauhaus.cs.washington.edu

  13. More host stuff • host -v 128.95.2.24 • Query about 128.95.2.24 for record types PTR • Name: poplar.cs.washington.edu • Address: 128.95.2.24 • host -t mx poplar • poplar.cs.washington.edu MX 10 june.cs.washington.edu • poplar.cs.washington.edu MX 20 trout.cs.washington.edu

  14. Active Names • Richer interface for name lookup • Motivation: • client side web replica search • name the service provided by • active networks • active services • network caches / transformation agents • Insight • We name services: IBM’s web service • We don’t care which host gives us the service

  15. What do we normally do to make big web servers? • Split it up, statically • java.sun.com • DNS round robin • www.microsoft.com (?) • can add new servers without telling anyone • Distributed director • connection level splitting • Neither consider locality of users • IP address and service not equivalent

  16. What could we do to make big web servers? • Help the user pick a close server • Download netscape or IE: • get a list of different places you can download from • how should you pick? • Shouldn’t the machine figure it out?

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