OPS335 Lab 3b

Some DNS Review

Last week we got an introduction to administering a simple authoritative DNS server. This week we'll review those topics, and learn a few more record types. You'll learn still more about DNS in your first assignment.

Also if you didn't become comfortable using the dig tool - you'll get more practice with it now.

MX Record

When someone tries to send email to senecacollege.ca - they actually want to send email to the Seneca mail server, which is not senecacollege.ca. That is a very typical setup for any business - it simplifies administration and helps a little with load balancing.

Find the MX record for senecacollege.ca using dig:

dig senecacollege.ca MX

Notice that the email servers aren't even a subdomain of senecacollege.ca but a completely different company (Microsoft in this case). In other cases (for example check the records for google.com) the email servers are within the company's domain.

In still other (rare) cases there is no MX record at all (check littlesvr.ca) - in that case the server that's at the IP for that domain is handling the email.

Notice that the response for your dig commainds for MX records contains domain names and not IP addresses. That means that when you look for a domain's email server - you may need to do a query for MX and another for A.

You should be comfortable reading and writing an MX record in the Bind configuration file. See the reference for the syntax.

CNAME record

Sometimes you want multiple domain names to point to the same server. The most common example of this is the www. subdomain. Use dig to find the main web server for Seneca or for CBC.

See the reference for CNAME to get examples of how to configure such records in Bind.