Barry britt systems support group department of computer science iowa state university
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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


Dev urandom

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% shareIIS: 21.1% share

    • November 2005

      • Apache: 70.9% shareIIS: 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”


Dev urandom

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


Dev urandom

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


Dev urandom

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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