ISP Changeover Question

[Chyka, Robert]

At a small remote research site of ours we are changing ISPs.  We have a
Exchnage Server and 2 web servers whose MX and A records are with our
currents ISP.  I have a question so we don't lose mail flow and I want
to make sure our web sites aren't down too long.
 
We are moving to Time Warner Business and they basically gave me the
power to create my own MX, A, PTR etc in their DNS with a login they
gave me.  They set up a DNS zone for our company.  Do I have to first
call our current provider and tell them that we are discontinuing our
service so they take our records out of DNS so I can add the new ones?
Or should I create the new MX record and give it a weight of like 30?
Currently we have a MX record with weights of 10 and 20 with our current
ISP.
 
I am figuring once I cut our connection over to Time Warner and I call
our current ISP to cancel our account that they will kill our MX record
and our 4 public IPS and A records we have.  I guess I am just a little
confused when I should create the new MX record and what I should do
with the current MX.
 
On the screen for MX record for our domain it has the following fields
to fill in:
 
Domain Name:
Host Value:
Mail Exchange:
Priority:
TTL:
 
I know what to put in for domain, what goes in the other slots.
 
Thanks for the help, I just CAN'T hinder mailflow for this branch at
all.
 
BC

~ Finally, powerful endpoint security that ISN'T a resource hog! ~
~ http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/  ~

Re: ISP Changeover Question

[Ben Scott]

On Tue, Apr 21, 2009 at 5:13 PM, Chyka, Robert bch...@medaille.edu wrote:
 We are moving to Time Warner Business and they basically gave me the power
 to create my own MX, A, PTR etc in their DNS ...

  It's generally easier if you separate your DNS hosting from ISPs
providing the feeds.  Changing feeds is complicated enough without
changing DNS hosting at the same time.  Most of the domain name
registrars throw in free DNS hosting these days, so this shouldn't
even cost a lot.  (If yours doesn't, find a better registrar.)

  The procedure for a change in nameservers is:

A1. Configure DNS zone with records to match existing DNS records at old ISP
A2. Change NS records at the registrar to point to the new nameservers
A3. Wait for any propagation delays (72 hours minimum is the usual
recommendation)
A4. Tell the old ISP you've switched to third-party DNS hosting and to
delete the zone from their nameservers
A5. Confirm previously-delegated nameservers at old ISP no longer
claim authority

  Once that's done, the procedure for a feed change is:

B1. Get new feed installed, tested, and up and running
B2. Change DNS records (A, MX, etc.) to specify new feed IP addresses
B3. Wait for propagation delays
B4. Confirm mail is coming in through new feed
B5. Unplug old feed
B6. Confirm everything still works
B7. Notify old ISP to terminate service

  Alternatively, if you want to keep DNS hosting with the feed providers:

C1. Configure DNS records at new ISP DNS to match your existing DNS
records at old ISP DNS
C2. Get new feed installed, tested, and up and running
C3. Notify registrar to change delegation to new ISP
C4. Wait for any propagation delays (72 hours minimum is the usual
recommendation)
C5. Change DNS records at both old ISP DNS and new ISP DNS to specify
new ISP feed
C6. Wait for propagation delays
C7. Confirm mail is coming in through new feed
C8. Unplug old feed
C9. Confirm everything still works
C10. Notify old ISP to terminate service

  You technically don't have to do step C2 until you do step C5, but
by getting it ready sooner you have more options in case things go
wrong.

  The delay for B3 (or C6) is directly proportional to how important
mail flow is.  The more important mail flow is, the longer you should
wait.  In theory, this delay should just be the TTL on your DNS
records, but it seems there are always some mail hosts that are
ignoring TTL for whatever reason.  Especially short TTLs.

  You can reduce propagation delays in the feed change step by
reducing the DNS TTL (Time To Live) values in advance of step B2 (or
C5).  TTL controls how long other DNS resolvers cache records for your
zone.  This is often a day or a week.  Reduce it to one day a week in
advance, then reduce it to an hour a day in advance.  Once the dust
settles, turn TTL back up.

 Do I have to first call our current
 provider and tell them that we are discontinuing our service so they take
 our records out of DNS so I can add the new ones?

  If you do that *first*, you'll prolly interrupt mail flow.  The old
ISP will remove the DNS records from their nameservers before the
delegation from the registrar has changed.

  If you're not familiar with how DNS works:

  There are registrars (Network Solutions, GoDaddy, Registrar.Com,
etc.).  Registrars process your domain name registration and publish a
delegation (NS records) for your domain.  The delegation tells the
rest of the world what nameservers to ask for information on your
domain.  Nameservers answer queries from the rest of the world.
Nameservers can be hosted anywhere by anyone.  You can host them
yourself, or the ISP providing the feed can do it, or the registrar
can do it, or a third-party company can.

  So when the rest of the world wants to look up, say,
microsoft.com, they first ask the authoritative nameservers for the
.com top-level domain, What's the IP address for microsoft.com?
The TLD nameservers says, I don't know -- ask ns1.msft.net.  The
rest of the world then find ns1.msft.net and asks, What's the IP
address for microsoft.com?  (This is an oversimplification, but it
will do.)

-- Ben

~ Finally, powerful endpoint security that ISN'T a resource hog! ~
~ http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/  ~