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Philip,
Re: ISP Change & Office Relocate
From: Mitch Kahn
Date: Friday, February 16, 2001
Time: 9:38:00 am
Here is what we are in the middle of doing right now. No one on the
list shot it down when I proposed this last week although Chris
Buxton from Men & Mice suggested that I misunderstood some of the
settings. I will append his comments following my plan below.
I hope that this helps.
Mitch Kahn
mitch@middlecoast.net
~~~~~~~~~~~~~~~~~~~~~
Background
A. We plan on moving to a new up line ISP soon. Since our clients get
hit by a lot of dial ups many of whom come from AOL we are concerned
about the amount of time that it takes for information to propagate
through AOL's DNS servers.
B. Since our ISP was supposed to have a secondary DNS server that
automatically picked up the settings from our primary we thought we
were covered. I have discovered that no setting changes have been
picked up by the secondary in months and many domains that we have
listed on our primary are not on the secondary at all. Several calls
to our ISP have gotten us nowhere.
C. In preparation for the move and change in IP addresses we have
developed the following strategy to minimize down time and
inaccessibility from the net. Any comments pro or con on our game
plan are welcome.
DNS Move Strategy
1. We have already changed the "Expire" settings to 86400 on each
domain and the "Minimum" and "Time-To-Live" to 3600. Two days before
the change over we will reduce "Expire" settings to 43200 on each
domain and the "Minimum" and "Time-To-Live" to 300. The night before
the move the "Expire" settings will be further shortened (amount to
be determined).
2. We really don't have a secondary DNS server so we believe that we
have nothing to lose by the following strategy: we plan to register a
new secondary DNS on the new IP addresses assigned by our new
provider. We will change the registration for the secondary on all of
our domains to our new secondary.
3. Our new secondary will be set up with the IP addresses that will
be assigned to the sites when the service changes over. Since this
secondary DNS server will not be accessible from the Internet until
we change over, the new information will not be available until we go
live.
4. When our new T-1 line is installed we will reassign the numbers on
our servers to the previously mapped out numbers on our new secondary
DNS server. Our primary DNS will be changed to our new IP address
range and a change of address will be filed with our registrar -
Network Solutions.
Our thinking is that since Ameritech (SBC) is painfully screwed up
and will not install our new line for at least three or four weeks
(and possibly as long as 60 days), the new secondary DNS server
information should be fully propagated throughout the Internet by
then. The primary will not be available when we move the router to
the new line, so the secondary server will provide all information.
The short "Expire" - "Minimum" and "Time-To-Live" settings should
force servers to update off the secondary (which will have more
standard settings so that it doesn't get pounded after the first
go-around).
5. After a week or so we will add a tertiary DNS server on someone
else's subnet and update Network Solutions to cover us incase our
connection goes down.
~~~~~~~~~~~~~~~~~~~~~
Chris Buxton's Comments:
Your plan sounds like it will work just fine, but I think you're
probably confused about the roles of the various values of the SOA
record (the Refresh, Retry, Expire, Minimum, and TTL values).
The only thing other people's DNS servers will ever pay attention to
is the TTL of whatever record they retrieve from your servers. The
TTL of any given record is determined as follows:
- If the record has an explicit TTL (as part of the record), use that.
- Otherwise, use the value from the Minimum field.
The TTL you see next to the Minimum field is the TTL for the SOA
record. It doesn't affect the rest of the zone in any way.
The Expire field is used by your secondary server. If the primary
server stops responding to requests from the secondary server, after
[expire] seconds, the secondary server will stop serving the domain.
This is generally not what you want to happen, though if a secondary
server is not reconfigured when the primary server is moved, you do
want it to stop serving the domain in a reasonable amount of time. To
balance the two, it is common to set the Expire field to a value
between 1 and 4 weeks.
____________________________________________________________________
At 5:08 AM -0500 2/16/01, p wrote:
>Hi all,
>
>Whats the considered wisdom for changing office and ISP without losing
>service to customers.
>
>I have a complex array of servers in old office with old ISP leased line,
>and an empty new office miles away with no servers and new ISP leased line.
>
>I want to move the servers from old office to new office with no loss of
>service.
>
>.We run primary and secondary QDNS 3 on 2 machines
>
>.Array of web servers + SAN
>
>.FTP server
>
>We could duplicate our network in the new location and then change our DNS
>IP addresses with the UK NIC. But if we can avoid purchasing new servers
>that would be a relief!
>
>Has any one done this recently?
>
>Any tips would be great!
>
>Yours
>
>Philip Edell.
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