>Wait between 16 and 24 hours for the new DNS information to properly
>propagate around the world, so if you sent an email to @jcws.net it
>recognizes the new MX information.
Just one quick note about DNS propagation. It can take anywhere from 0
seconds to many years to DNS changes to propagate. In almost all cases,
some servers will immediately query your DNS server for the change, while
others will take up to [X seconds].
"Propogation" is a misleading term. It makes it sound as though when you
make a change, it goes to other servers, and they send it on to other
servers, and so forth (kind of like how Usenet messages get spread). It
doesn't work that way, though.
When you make a change to your DNS server, there are probably lots of
servers out there that have recently (within [x seconds]) queried your DNS
server for information. For example, they may ask your DNS server for the
MX record for your domain. Your server will respond with the MX record,
and a "TTL" ("Time To Live") value of [x seconds]. You can set this to be
whatever you want. Servers will then cache the information for those [x
seconds]. If they need to know what your MX record is, and those [x
seconds] haven't elapsed yet, the server will use what it was given before
(since you told them it was OK to hold on to the information for [x seconds]).
So, assume that your TTL is 3600 seconds (and you didn't have any longer
TTLs that could still apply; if you used to have a TTL of 1 month and
changed it 2 weeks ago, you'll still have cached info on DNS servers). In
that case, if you make a change to your DNS, "propagation" will take no
more than 1 hour. On the other hand, if your TTL was set to 1209600
seconds, it will take up to a week for the information to propagate.
A couple things I haven't pointed out:
o Different records can have different TTL values, which can confuse
things; fortunately, most people use the same
TTL for all the records on their domain.
o If you change DNS servers (which requires a change at root), it could
take up to about 72 hours for the change to
take effect (typically up to 24 hours for the root servers to make the
change, and up to 48 hours for the cached data
to become stale)
o Once you have made a change to your DNS, there is no easy way to find out
what your old TTL value was if you
changed it. If you don't know completely what you are doing, you
could have a 2 week TTL and change it to
1 day. That's good, but if you don't remember that the old TTL was 2
weeks, you'll never be sure that everyone
knows about the change.
-Scott
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