Email, DNS, and P2P Protocols

Tom Kelliher, CS 325

Feb. 7, 2011

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Assignment

Written assignment.

Review examples, in notes and textbook, of using telnet to exchange protocol messages with application services.

See me if you don't remember your phoenix username/password.

From Last Time

Application layer, HTTP, and FTP.

Outline

  1. SMTP, POP, and IMAP protocols.

  2. DNS.

  3. P2P.

Coming Up

Protocols lab.

Email protocols

The overall model:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_16.eps}\end{figure}

Sending email:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_18.eps}\end{figure}

  1. Email service in the traditional Unix model.

  2. Email service with a standalone GUI client: POP and IMAP.

  3. Email service with a web-based GUI client.

  4. Email service with a Blackberry device.
    1. Push vs. pull architectures.

    2. What are the design models we could consider?

    3. What model does RIM use?

  5. Use of MX records.

DNS

Historical context:

  1. How was name resolution initially performed?

  2. What was wrong with that?

Features of today's DNS:

  1. A FQDN and its components: bluebird.goucher.edu.

  2. Hierarchy.

  3. Delegation of authority.

  4. Redundancies: multiple root servers; primary and secondaries.

  5. Two components: the resolver and DNS service. Finding a DNS server.

    How the hosts file is used.

  6. Caching servers. Priming the cache.

    TTL field.

    Stale entries and flushing the cache.

  7. A and PTR records. Some other records types: SOA, NS, MX,

    TXT records and Sender Policy Framework (SPF) information for reducing SPAM.

  8. Vulnerabilities: DDOS, cache poisoning, hosts file attacks.

A view of the hierarchy:

\begin{figure}\centering\includegraphics[]{Figures/fig02_19.eps}\end{figure}

Anatomy of a DNS query:

\begin{figure}\centering\includegraphics[width=4in]{Figures/fig02_21.eps}\end{figure}

Format of a DNS server response:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_23.eps}\end{figure}

  1. Why does phoenix have two IP addresses?

  2. DNS implications under this scenario.

P2P

The file distribution problem:

\begin{figure}\centering\includegraphics[width=4in]{Figures/fig02_24.eps}\end{figure}

Scalable vs. unscalable architectures:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_25.eps}\end{figure}

BitTorrent chunking:

\begin{figure}\centering\includegraphics[width=4in]{Figures/fig02_26.eps}\end{figure}

Centralized indexing service:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_27.eps}\end{figure}

Distributed indexing service; query flooding:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_28.eps}\end{figure}

Limiting scope with a hop count field.

A hybrid approach:

\begin{figure}\centering\includegraphics[width=5in]{Figures/fig02_29.eps}\end{figure}


Thomas P. Kelliher 2011-02-06
Tom Kelliher