DNS - Load balancing

● For some sites, e.g. google, facebook, zing, no single hardware (server) can handle such big traffic – Multiple server for one domain – Fault tolerance ● Question – Choose this or that? – or keep them equal (load balancing) Reliability ● DNS servers are replicated – Name service available if ≥ one replica is up – Queries can be load balanced between replicas ● UDP used for queries – Need reliability → must implement this on top of UDP! – Why...

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The Domain Name System

● The DNS is an Internet-wide distributed database that translate between domain names and IP addresses ● Times before DNS (1985) – Using HOSTS.txt file under, e.g., /etc/hosts – Download from server through FTP regularly – Many more downloads – Many more update Hence, DNS But, why not centralize DNS? – Single point failure – Traffic volume – Distant centralized database – Single point of update → Doesn't scale DNS goals ● Basically a wide-area...

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Cookies: Keeping “State”

Many major Web sites use cookies                                   Four components: 1) Cookie header line in the HTTP response message 2) Cookie header line in HTTP request message 3) Cookie file kept on user’s host and managed by user’s browser 4) Back-end database at Web site Example: - Susan accesses Internet always from same PC - She visits a specific e-commerce site...

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HTTP Basic

HTTP layered over bidirectional byte stream – Almost always TCP ● Interaction – Client sends request to server, followed by response from server to client – Requests/responses are encoded in text ● Stateless – Server maintains no information about past client requests  HTTP Request  Request line – Method ● GET – return URI ● HEAD – return headers only of GET response ● POST – send data to the server (forms, etc.) – URI ● E.g. http://www.intel-iris.net/index.html...

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Applications (Example with HTTP and FTP)

Some parts of this presentation are copied from ● Roger Dannenberg, Srinivasan Seshan, lecture notes in Computer Network, CMU http://www.cs.cmu.edu/~srini/15-441/F11/ ● Jorg Liebeherr, lecture notes in Internet Engineering, Virginia Uni., http://www.cs.virginia.edu/~cs458/ ● TCP/IP Protocol Suite lecture notes, The McGraw-Hill Companies, Inc., 2000 Client-Server Paradigm                      ...

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