Untangling the Web from DNS Michael Walfish Hari Balakrishnan Massachusetts Institute of Technology Scott Shenker UC Berkeley/ICSI IRIS Project 30 March 2004

Introduction The Web depends on linking; links contain references Properties of DNS-based references encode administrative domain human-friendly click here These properties are problems!

Web Links Should Use Flat Identifiers <A HREF= >my friends dog <A HREF= >my friends dog <A HREF= >my friends dog <A HREF= >my friends dog Current Proposed This talk: That we should build this That we can build this

Outline I.Argue for flat tags instead of DNS-based URLs II.Resolution service for flat tags

Status Quo DNS IP addr a.com Browser HTTP GET: /dog.jpg <A HREF= >Spot <A HREF= >Spot Web Page Why not DNS? Reference Resolution Service

Goal #1: Stable References Stable=reference is invariant when object moves In other words, links shouldnt break DNS-based URLs are not stable...

Object Movement Breaks Links isp.com dog.jpg isp-2.com spot.jpg HTTP 404 HTTP GET: /dog.jpg Browser <A HREF= >Spot <A HREF= >Spot URLs hard-code a domain and a path

Object Movement Breaks Links, Contd isp.com dog.jpg isp-2.com spot.jpg HTTP 404 HTTP GET: /dog.jpg Browser <A HREF= >Spot <A HREF= >Spot Todays solutions not stable: HTTP redirects need cooperation of original host Vanity domains, e.g.: internetjoe.org now owner cant change

Goal #2: Supporting Object Replication Host replication relatively easy today But per-object replication requires: separate DNS name for each object virtual hosting so replica servers recognize names configuring DNS to refer to replica servers isp.com /docs/foo.ps mit.edu ~joe/foo.ps HTTP GET / host: object26.org HTTP GET / host: object26.org

What Should References Encode? Observe: if the object is allowed to change administrative domains, then the reference cant encode an administrative domain What can the reference encode? Nothing about the object that might change! Especially not the objects whereabouts! What kind of namespace should we use?

Goal #3: Automate Namespace Management Automated management implies no fighting over references DNS-based URLs do not satisfy this...

DNS is a Locus of Contention Used as a branding mechanism tremendous legal combat name squatting, typo squatting, reverse hijacking,... ICANN and WIPO politics technical coordinator inventing naming rights set-asides for misspelled trademarks Humans will always fight over names...

Separate References and User-level Handles So arent you just moving the problem? Yes. But. Let people fight over handles, not references Object Location Human- unfriendly References User Handles (AOL Keywords, New Services, etc.) tussle space [Clark et al., 2002]

Two Principles for References 1.References should not embed object or location semantics 2.References should be human-unfriendly Flat tags Minimal interface Natural choice:

Outline I.Argue for flat tags instead of DNS-based URLs II.Resolution service for flat tags: SFR Object Location Flat Tag User Handle (AOL Keyword, New Handle, etc.)

<A HREF= >Spot <A HREF= >Spot Managed DHT-based Infrastructure GET(0xf012c1d) ( , 80, /pics/dog.gif) o-record HTTP GET: /pics/dog.gif Web Server /pics/dog.gif SFR in a Nutshell orec API orec = get(tag); put(tag, orec); Anyone can put() or get()

Resilient Linking SFR <A HREF= >here is a paper <A HREF= >here is a paper HTTP GET: /docs/pub.pdf /docs/ HTTP GET: /~user/pubs/pub.pdf ( ,80, /docs/) ( ,80, /~user/pubs/) /~user/pubs/ tag abstracts all object reachability information objects: any granularity (files, directories, hosts)

(Doesnt address massive replication) Flexible Object Replication (IP1, port1, path1), (IP2, port2, path2), (IP3, port3, path3),... 0xf SFR o-record Grass-roots Replication People replicate each others content Does not require control over Web servers

Reference Management Requirements No collisions, even under network partition References must be human-unfriendly Only authorized updates to o-records Approach: randomness and self-certification tag = hash(pubkey, salt) o-record has pubkey, salt, signature anyone can check if tag and o-record match

Latency Problem: Lookups should be fast Solution: lots of TTL-based caching Clients and DHT nodes cache o-records DHT nodes cache each others locations In Chord, aggressive location caching 2 or 3 hops per lookup Could also use one-hop or Beehive

Outline I.Argue for flat tags instead of DNS-based URLs II.Resolution service for flat tags: SFR III.Related Work / Summary / Conclusion

Related Work URN (Universal Resource Name) DOI: an existing URN implementation PURL (Permanent URL) Globe Open Network Handles DNS over Chord

Summary Should we build flat references for the Web? Yes! Can we build flat references for the Web? Yes! (Our implementation is usable.) Lots of future work...

Conclusion DNS-based URLs certainly convenient! But flat tags better for linking Future: type DNS names, link with flat tags?

Appendix Slides

Implementation HTTP SFR Web Proxy SFR Client SFR Portal Chord DHash SFR Server Web Client Proxy allows: End-users to experience SFR latency Dynamic population of SFR infrastructure with o-records orec = get(tag) put(orec,tag) HTTP SFR Portal GetRequest GetResponse PlanetLab

Evaluation SFR data eight day trace 390 virtual hosts; 130 nodes in Chord ring on PlanetLab latency seen by SFR portal most queries are two hops informal feedback: generally indistinguishable from DNS Comparison meant to be suggestive not conclusive DNS data collected at MIT CSAIL, Feb. 2004

SFR Components Portal Relay Org Store SFR Infrastructure Organization Infrastructure stores (tag, o-record) pairs Caching throughout; o-record has TTL field SFR Client Application SFR Client Application SFR Client Application SFR Client Application

Portal Relay Org Store SFR Infrastructure Organization Fate Sharing put(tag,orec) get(tag) Fate sharing via write-locality Simple case... SFR Client Application SFR Client Application SFR Client Application SFR Client Application

Alternate SFR Design: SFR-- SFR stores only pointers to organizations Analogous to NS records in DNS GET(0xf012120) org ptr: x User SFR Infrastructure x GET(0xf012120) meta-data (IP addr, etc.) Organization

When Files Separate From Directories SFR <A HREF= >here is a paper <A HREF= >here is a paper HTTP GET: /doc/pub3.ps /doc/pub1.ps HTTP GET: /abc/pub3.ps ( ,80, /doc/) redirect ptr: x /abc/pub3.ps /doc/pub2.ps /doc/pub3.ps x GET(0xf012012)

Location Caching Simulate effect of location caching 20 lookups/sec; one failure and one birth per 10 sec. Timeout rate: 4% 1000 nodes