March 2007
Intermediate to advanced
304 pages
11h 12m
English
Content preview from Linux System Administration
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Chapter 3: The Domain Name System
The use of CNAME records has pros and cons. Many DNS specialists advise against
their use. Still, you might find that
CNAME records have some value. For example, if
your DNS directory contains many
A records pointing to the same IP address and you
move to another hosting service that assigns a different IP address, you’ll have to
update every
A record. But if you have just one A record and all your other host-
names are in
CNAME records, you’ll only have to update one A record. So, we believe
that
CNAME records still have a place in the DNS pantheon.
TXT and SPF records.
TXT records let you add text to a zone. People primarily use TXT
records to embed SPF (Sender Policy Framework) records, which control whether
mail exchangers should accept email addressed from their domains. The larger email
providers, such as Yahoo! and Hotmail, now rely heavily on
SPF records to prevent
spammers from forging email addresses with the providers’ domain names. If email
arrives from a machine that is not listed in the
SPF record, an MTA may classify it as
spam.
A wizard for creating
SPF records can be found at http://www.openspf.org/wizard.
html?mydomain=&x=26&y=8. We used this wizard to create two
SPF records for
centralsoft.org, then embedded them in
TXT records and added them to our zone file:
centralsoft.org. TXT "v=spf1 a mx ~all"
server1.centralsoft.org. TXT "v=spf1 a -all"
Putting ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.