[cs615asa] HW#4 grades

Jan Schaumann jschauma at stevens.edu
Sun Apr 8 23:34:42 EDT 2012


Hello,

I've just sent out grades for HW#4.  If you have not received a grade,
please let me know ASAP.

Here are a few things you may wish to review in this context:

- Make sure you understand what a caching DNS resolver is and what the
  point of the first part of the exercise was.  You do NOT want to point
  your DNS server to a forwarder, since that would mean your server is
  not doing any of the real resolution we're looking to trace.

- Make sure you understand all the traffic going around in your tcpdump.
  When you are tracing DNS related issues, you probably want to avoid
  having the host doing the tracing generate additional lookups, such as
  a reverse lookup for each and every packet it sees.  Use of '-n' is
  probably advised.

- Review the use of the 'helo' part of the SMTP protocol.  What is it
  used for?  What is the correct or most suitable hostname to pass?

- Think about how email works - is the fact that the server accepts any
  email from anybody anywhere a problem?

- I saw some very nice debugging and reading of the tcpdump packets in
  this part.  Remember that you can see ascii and hex.

- Think about why traceroutes from certain hosts to other hosts time
  out, but why they may work from a second host elsewhere.  If you have
  a suspicion for a reason, what, if anything, can you do to work around
  that problem?

- Most of you noted with some surprise that traffic to Hawai`i appears
  to always go through Littelton, CO.  Research why that might be.

-Jan


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