Computer networks -- 2008-2009 -- info.uvt.ro/Course 11

Quick links: front; agenda; courses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13; examination.

Please note that the current work serves mainly as general guidance and discussion topics, and is by no means the reference material for the course. For further information please consult the dedicated section.

DNS

overview:
- DNS (Domain Name System);
- definition: hierarchical distributed database containing essential information for the Internet;
- main purpose: to translate between human readable names and computer usable binary data;
- its relation with hosts file;

characteristics:
- distributed both in administrative and technical sense;
- fault tolerant as a consequence of its distributed nature;

Domain name hierarchy

domain name hierarchy:
- a tree composed of nodes;
- each node is identified by a domain name;
- each node holds one or more records;
- the tree is decomposed into disjoint sub-trees, named zones;
- one zone can be decomposed further into sub-zones;
- the first level of the tree contains the root zones;

domain names:
- a domain name is represented by a tuple of strings (parts) separated by dots; (for example www.google.com is the domain name; www, google and com are the labels;)
- the right-most part is called a TLD (Top Level Domain);
- a name could be relative or absolute;
- FQDN (Fully Qualified Domain Name);

actors (client / server processes):
- name server:
  - authoritative;
  - non-authoritative;
- resolvers:
  - recursive / non-recursive resolver server;
  - caching resolver server;
- important name servers:
  - root name servers;
  - top level name servers;

Domain name resolution

address resolution process;

stored information:
- host names;
- email servers;
- informative notes;

resource records (RR):
- name: domain name relative to the zone name;
- type:
  - A: used to hold the IP associated with the current node;
  - NS: denotes a delegated name server for the designated zone;
  - MX: denotes a delegated mail server;
  - CNAME: instead of giving an associated IP give an alias for this name;
- class:
- value: depending on the type;
- TTL (Time To Live);

implementations:
- BIND (Berkeley Internet Name Domain);
- djbdns;

miscellaneous:
- DynDNS;
- open resolvers;

links:
- Wikipedia -- Domain Name System;

Network architectural aspects of well known protocols

HTTP

characteristics:
- reply / request oriented;
- stateless protocol;

actors:
- user agent: web-browser, etc.;
- server:
  - origin server;
  - proxy:
    - caching proxy;
    - reverse proxy;
    - transparent / non-transparent proxy;
  - gateway;
  - tunnel;

important aspects:
- caching;
- keep-alive;
- pipelining;

FTP

...

connection types:
- passive;
- active;

SMTP

...

SMTP relays;
SMTP dialogue example;

Miscellaneous

virtual hosts;
load balancing:
- replication;
- DNS round-robin balancing;

The current page is (in almost all parts) a recompilation of the following pages (from previous year):

conf. dr. Victoria Iordan, iordan@info.uvt.ro
Ciprian Dorin Craciun, ccraciun@info.uvt.ro
Marian Neagul, marian@info.uvt.ro