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Barry Britt, Systems Support Group Department of Computer Science Iowa State University. /dev/urandom. Outline. DNS Samba Apache NAT & routing. DNS. How does your machine find out that: popeye.cs.iastate.edu => 129.186.3.66 Domain Name System

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barry britt systems support group department of computer science iowa state university
Barry Britt, Systems Support Group

Department of Computer Science

Iowa State University

/dev/urandom
outline
Outline
  • DNS
  • Samba
  • Apache
  • NAT & routing
slide3
DNS
  • How does your machine find out that:
    • popeye.cs.iastate.edu => 129.186.3.66
  • Domain Name System
    • Consists of name servers, each responsible for “domains”
    • What are domains?
      • .edu
      • .com
      • .org
      • .iastate.edu
dns querying
DNS querying
  • Every FQDN (Fully Qualified Domain Name) has an implied \'.\' at the end of it
    • popeye.cs.iastate.edu.
    • www.google.com.
    • en.wikipedia.org.
  • Queries are handled by the DNS servers referenced on your computer.
    • /etc/resolv.conf on most Linux machines
anatomy of a dns query
Anatomy of a DNS Query
  • How does your machine know what to do?
  • RFC 1035 (DNS Protocol Specification)
    • Says, start at the end and work to the beginning.
    • Let\'s query: www.google.com.
more dns
More DNS
  • Queries must be done for every host name (but results are cached for a period of time)
  • Note:
    • One server process can be a client process for another service
  • e.g. - network time protocol (NTP)
    • Queries a time server (time.iastate.edu) for the correct time.
    • Uses DNS to resolve time.iastate.edu
samba
Samba
  • What is it?
  • Short Answer: Software that allows a UNIX machine to work as a Windows File Server
  • Long Answer:
    • M$ uses a protocol called CIFS for file sharing (Common Internet File System)
    • M$ uses a transport protocol for CIFS called SMB (Server Message Block)
    • Samba is an implementation of SMB/CIFS that runs on many types of machines
samba history
Samba History
  • 1992 → Andrew Tridgell
    • Wanted to connect DOS PC and UNIX Server AND
    • Wanted to use NetBIOS on both
  • So... he accomplished this by:
    • Writing a packet sniffer
    • Reverse engineering the SMB protocol
    • Implementing this on a UNIX machine so that it behaved like a
    • Then, he released the code to the public
samba history1
Samba History
  • 1994 → Tridgell wanted to link wife\'s windows machine to his Linux network.
    • Tried his old code, and it worked!
  • 1999 → Samba 2.0 is released
    • Testing shows that Samba 2.0 is 2x faster than Windows 2000 Server
  • 2003 → Samba 3.0 is released
    • Testing shows that Samba 3.0 is 2.5x faster than Windows 2003 Server
samba misc info
Samba Misc. Info
  • Samba project is HUGE (www.samba.org)
  • Samba is mentioned in the famous “Halloween Memo” from Microsoft (leaked memo in the late 80\'s)
  • License is GPL
  • Server can be any (or all) of the following:
    • NetBIOS (name resolution) server
    • Domain Browser
    • Authentication server
    • File & Print Server
samba misc info1
Samba Misc. Info
  • Client
    • Feels like it\'s talking to a Windows Server
      • Can Mount files
      • Can get NetBIOS resolution
      • Can authenticate to Samba server
      • Can browse the Domain
  • For More Info....
    • SMB How-To at www.tldp.org
    • Official How-To at www.samba.org
      • Chapter 2
  • You WILL be doing this in Lab.
apache
Apache
  • License: Apache Software License (ASL)
    • Free software license, similar to GPL but allows for patented software inclusion.
    • Why? Want 3rd party contributions from companies.
  • Known for...
    • HTTP Server
    • Apache 1.0 → release 1995
    • After 1 year, Apache is the #1 web server on the Internet
apache1
Apache
  • Today:
    • Apache is the #1 web server on the internet
    • October 2004
      • Apache: 67.9% share IIS: 21.1% share
    • November 2005
      • Apache: 70.9% share IIS: 20.2% share
  • Runs on all major platforms, and some non-major ones too
  • Runs sites that get tens of millions of unique hits per day
apache2
Apache
  • Customization
    • Apache uses modules that are can be loaded at compile time or run time
  • Why use Apache?
    • Acc\'d to netcraft “Most Reliable Hosting Company” as of Aug 2010, out of the top 10:
      • 8 are Linux based
      • 2 are Free BSD based
  • Apache/Linux runs the content on the Internet
apache for lab
Apache for Lab
  • You will
    • Set up a basic HTTP server
    • Static content
      • HTML pages that sit on a location on the server
    • Dynamic content
      • Pages that are constructed by the server
      • Output because of:
        • Executable (C or some other language)
        • Script (CGI, bash script, etc...)
apache for lab1
Apache for Lab
  • References
    • Chapter 26 of textbook
    • Many apache how-to docs at www.tdlp.org
    • Apache documentation
      • httpd.apache.org
    • www.apache.org
routing
Routing
  • Router
    • Device that interconnects 2 or more computer networks
  • Example: a home network
    • 2 IP address, one for each network
routing1
Routing
  • Router\'s Job
    • Any traffic from 192.168.0.x subnet
      • Destined for internet → forward to 203.176.5.49
      • Destined for local → resend internally
  • Hosts specify the router\'s internal address as “gateway”
slide19
NAT
  • Network Address Translation
    • Actually modifies the network addresses in the IP packets
    • Why?
      • IP Masquerading → the NAT Router sends all traffic AS ITSELF
      • The outside world cannot see the 192.168.0.x subnet (private network)
  • Therefore, we can “share” the internet connection from our ISP over our home network, ISP has no way to tell
slide20
NAT
  • Some IP address blocks are reserved for private networks
    • 10.0.0.0 – 10.255.255.255 (24 bit block)
    • 172.16.0.0 – 172.31.255.255 (20 bit block)
    • 192.168.0.0 – 192.168.255.255 (16 bit block)
  • All these ranges are safe to use for private networks
slide21
NAT
  • NAT has significantly slowed the consumption of IPv4 addresses.
  • Delay of Ipv6 adoption is primarily due to NAT
  • How many devices connected to Internet?
    • Recent estimate: > 5,000,000,000
    • Over IPv4 limit of 232
  • Google Server Farm(s) may have > 10,000 all inside of private IP space using NAT
    • Only the front-end “gateway”s need proper IP addresses
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