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?