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Protocol Problems and Architectural Issues

Steven M. Bellovin AT&T Labs – Research smb@research.att.com http://www.research.att.com/~smb. Protocol Problems and Architectural Issues. Different Kinds of Problems. Directory versus lookup Surprising results Chokepoints Preemption. Directory Versus Lookup.

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Protocol Problems and Architectural Issues

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  1. Steven M. Bellovin AT&T Labs – Research smb@research.att.com http://www.research.att.com/~smb Protocol Problems and Architectural Issues

  2. Different Kinds of Problems • Directory versus lookup • Surprising results • Chokepoints • Preemption

  3. Directory Versus Lookup • A directory provides an imprecise, often interactive service • A lookup system provides reproducible, predictable answers, suitable for use by programs • The DNS was designed to be the latter

  4. Surprising Results • Programs no longer do what you expect • Sometimes there is incorrect behavior; sometimes, an error presents itself differently

  5. Preemption • The Internet empowers the endpoints, not the middle • Endpoints – applications, hosts, etc. – can best decide how to handle error cases such as non-existent host name • Wildcards pre-empt that ability and put control in the center

  6. What is the Internet? • TLD wildcards worked more-or-less adequately for (most) Web work and ordinary email. • The IAB noted that wildcards in general are mostly used for email only. • TLD wildcards do not work well for other protocols. • What is the minimum common protocol set for the Internet?

  7. The Hourglass Model • Historically, the Internet architecture has been modeled as a hourglass: “Everything over IP, and IP over everything.” • Is the new model “Everything over HTTP”?

  8. Today's Hourglass App App App TCP UDP ... IP ... Ethernet Wireless

  9. Tomorrow's Hourglass? App App App HTTP TCP IP ... Ethernet Wireless

  10. Where Do Services Originate? • Most interesting new services come from the edges • Often, neither the ISPs nor the IETF are involved, most notably in the early days of the Web. • One part of the center's job is to stay out of the way of others' innovation – we don't want to lock in the Internet into the mostly-http model

  11. Why Wildcards CanBreak Things • The DNS does not know what application the user wants • Is that an ancient mistake? • It mirrors the division of responsibility between IP and the upper layers • A service intended for one or two purposes will often fail for other purposes. • Even “normal” services can be complex

  12. Conclusions • The Internet is built on a set of architectural assumptions • This architecture encouraged innovation • Breaking the architectural model will cause unforseeable failures, both in less-common existing software and for future ideas

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