Subject:  Wireless Networking Tips
Date:     Wed Dec 14 01:18:38 PST 2005


Here are some tips and guidelines for preventing networking problems
for yourself and your neighbors.

  1.  Verify your computer or laptop has the latest BIOS and network
      drivers!

      Network technology is constantly evolving.  Many new PCs are
      shipped with drivers which may be unsuitable for current
      networking standards and conditions.  Check with your
      manufacturer for patches and updates which may resolve recently
      discovered network issues.

  2.  Don't connect to the Wireless and the Wired networks at the same
      time!

      Simultaneous connections to the wireless and the wired networks
      confuse the networking equipment.  If in addition you are using
      a Network Bridge, this will cause network loops, which can
      stymie traffic.

      Most laptops come programmed with keyboard buttons to disable
      the wireless network card.  Typically,

        Dell:     Fn-F2
        Toshiba:  Fn-F8

      Use the keyboard buttons to turn off the wireless if you are
      connected to the wired network.  Some Toshiba laptops also have
      hardware switches for turning off the wireless transceiver, but
      these do not disable the software, and so are not effective in
      preventing networking conflicts.

      Some laptop manufacturers provide special software, which can be
      configured to manage simultaneous network connections.  For
      example, the latest Toshiba Tecra A4 laptops include the
      Toshiba ConfigFree Utility, which automatically detects whether
      or not the laptop is connected to the wired network, and
      enables/disables the wireless connection correspondingly.

  3.  Do not use Windows XP Network Bridges!

      A network bridge is used for sharing your network connection
      with other computers.  A network bridge routes traffic through
      your computer, resulting in a slow performance and problematic
      connection for both your computer and other computers which
      inadvertently wind up getting sucked through the lengthy detour
      of your network card.

  4.  Do not use IPv6!

      This experimental network protocol has not been standardized
      yet.  Almost every instance of this protocol encountered on our
      campus network has disrupted entire subnets.

      In the past, Windows Updates would offer users the opportunity
      to install this module, touting future improved performance and
      reliability.  Unfortunately, it hasn't been adopted yet, and so
      it has only caused network havoc.  Probably for these reasons,
      Microsoft has discontinued posting this at the top of the
      list of "Recommended Windows Updates".

  5.  Know that the MAC timeout is about 5 minutes!

      It takes about 5 minutes for the campus Cisco networking
      switches to recognize whether any given network hardware address
      has been previously seen on the network.  (This is a design
      feature that was implemented by Cisco in response to security
      vulnerabilities caused by rogue DHCP servers, and other threats
      swamping the network with excessive addresses and broadcast
      traffic.)  Hence, it may take up to 5 minutes for the DHCP
      servers to reissue you a new DHCP address if you suddenly switch
      between reconnecting between the wireless and wired networks or
      between offices and labs on the same subnet, for example, NET38.

      It may be gentler on the network and quicker too, if you would
      formally release your IP address on the old network, for
      example, by using,

        ipconfig /release

      before reconnecting to the new network, you request a new
      DHCP address using,

        ipconfig /renew

      It isn't a problem if you switch between different locations
      which are on different subnets, for example, between Kerckhoff
      and Crellin.

  6.  Call me immediately, if you are experiencing network troubles!

      In the last few months, we have had dealt with a number of
      network disruptions caused by a variety of sources.  It appears
      we have resolved all these problems I know about.  If you are
      still having problems let me know, so that we can diagnose them
      in real time.  There isn't any good way to diagnose shadows of
      signals long past, after you have unplugged from the network and
      gone home.

      Phone me at x4554, or leave a voice message if you cannot reach
      me in person.  If it is a widespread network outage, and you
      cannot reach me, phone the IMSS Help Desk, x4602.

      It would be helpful if you would record the date, the room, the
      exact time of day, the location and the numbers printed on the
      network wallplate, which identify the Ethernet port you're
      using, along with the symptoms you're encountering.  It would be
      helpful if you would include diagnostics such as the output of,

        ipconfig /all

      which also lists the physical address of your network card.  To
      record the output of this utility, pipe the contents to a text
      file, for example run,

        ipconfig /all > C:\network.txt

      and then send me the contents of the text file, C:\network.txt.
      Equivalently, on Mac OS X, run the command from Terminal,

        ifconfig -a > network.txt

---Pam