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Linux 2004
Conference and Tutorials
Thursday 5th to Sunday 8th August
Leeds, West Yorkshire

Niall Mansfield - UIT Cambridge Ltd.

TUTORIAL: Linux Networking Troubleshooting


A linux-based introduction to TCP/IP networks. The emphasis is practical rather than theoretical, covering situations you're likely to encounter.
We use everyday tools to show you what's happening on your network. This helps you understand the TCP/IP at a deeper level and is also great for troubleshooting.


TCP/IP is very simple, and consists of many, easily-understood building blocks. These can be put together to build extremely complex networks (in the same way that individual chess moves are very simple, but chess matches can be complex.)

What you will learn

  • how to configure machines to operate correctly on your LAN and across the Internet
  • how to troubleshoot just about any networking problem

Who should attend

  • technical staff, technical managers, or technical sales
  • consultancy and services staff installing or managing customer networks
  • people using TCP/IP networks every day ...
  • who are managing and building networks, or ...
  • who are responsible for an organization's applications and systems as a whole
  • people building TCP/IP networks at home
  • anyone connecting to the Internet
  • students at any level studying computer networks


  • TCP/IP is a packet-switching network
    • How that helps us -- we can use a "packet sniffer" to see what's happening. (The network admin's equivalent of the electrical engineer's oscilloscope.)
  • Tools (free, open-source)
    • The tcpdump packet sniffer
    • The ethereal protocol analyzer
    • Installing and using the tools
  • TCP/IP networking is in layers
  • The IP layer
    • hardware independent (important to allow LANs to grow into what became the Ethernet -- same networking system for LAN and WAN)
    • IP addresses and what they mean
  • Ethernet -- the most usual hardware layer
    • how Ethernet addressing works
    • ARP (address resolution protocol) links the Ethernet hardware to the high-level IP layer
    • watching ARP with a sniffer
    • common problems
  • What a netmask is
    • a netmask + an IP address specifies a range of IP addresses
    • most common use is to say "this range of IP addresses is connected to my local wire"
    • any addresses not in that range can only be reached by a ...
  • Routers, and routing
    • how IP routing works (conceptually very simple, but very powerful)
    • the idea of the default gateway
    • routing tables
    • troubleshooting routing problems
    • using more than one router: the 'route' command
  • The DNS - domain name system
    • what the DNS is all about -- convert a host name to a numeric IP address
    • how information is stored in the DNS -- A, PTR, MX, CNAME, TXT and SOA records
    • configuring a machine to use the DNS
    • common DNS problems
    • what "reverse lookups" are (convert a numeric IP address to a name)
  • Higher level protocols
    • TCP makes it easy to have networked applications
    • what TCP gives us -- reliable data transfer even when there are problems on the network.
    • How e-mail uses TCP -- SMTP and POP.
    • Troubleshooting e-mail
    • The UDP and ICMP protocols

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