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

• 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

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)

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

2 - 4

• In slow start, each ack increases cwnd by one.

• Delayed acks not really shown here.

Homework 2 - 5

• I don’t know yet. :)

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

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?

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

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

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

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

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

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?