Changing IP address for my site - any issues?

[smn2]

Hi,

I'm thinking of changing IP address for my site -
something I seem to be able to do at the click
of a button, with my webhost.

I want my site to have a unique IP address.

What I want to know is what issues, if any,
should I be aware of before I click the switch?

Thanks in advance,

Steve

[dmorison]

The only issue (unless you take steps to mitigate it) is that for a period, some users, including search engine spiders, may be unable to find your site because of "DNS Caching".

When an IP address is looked up by a DNS server, one of the parameters that is returned is a Time To Live value (TTL), sometimes called "Minimum". This value tells the requesting DNS server how long it can hang on to the result for in order to save repeated requests to the authority DNS servers for your domain (the ones listed in your "whois" record).

Now, this value can be anything from nothing to weeks; so what effect an IP address change has on your users depends on:

a) What is it now?

If it is zero, there is no problem. Change your IP address and away you go. If it is not zero, then:

b) Can you change it?

If you can't change it, there's not a lot you can do. Go ahead and make the change and accept that there is the possibility that, for whatever period it is currently set to, that a few users may experience an outage.

If you can change it, then:

c) Can you wait for at least the current setting before changing IP?

If you can, then simply set it to zero, wait for whatever it was set to before, and then change your IP. Then you can set it back to a higher value to avoid unnecessary load on your authority server.

With regards to the situation with search engines and what happens when a spider gets a 404, I don't think there is a definitive answer. In my experience, Google at least is extremely forgiving. Pages certainly aren't dropped at the first whif of a 404 or server outage. I've got pages still indexed in Google that haven't been online for over 15 months!

Hope this helps!

[smn2]

Hi,

It does help, thank you, but...

When an IP address is looked up by a DNS server, one of the parameters that is returned is a Time To Live value (TTL), sometimes called "Minimum". This value tells the requesting DNS server how long it can hang on to the result for in order to save repeated requests to the authority DNS servers for your domain (the ones listed in your "whois" record).

How can I find out if I can change this value?

Steve

[dmorison]

Whether you can change TTL (Minimum) or not is basically down to how "advanced" your ISP's DNS control panel is.

Many don't make the parameter available to customers because they shield the complexities of DNS behind a much simpler interface, such as the option I think you have to change the IP address using a drop down. On your control panel, look out for things like "Advanced Settings" or something like that.

If you want to find out what it is now, you can use the nslookup command. The syntax is the same on a Linux or Windows box:

C:\>nslookup <return> > set querytype=soa <return> > www.yourdomain.com <return>

That will generate an output including, amongst other things:

Non-authoritative answer: www.yourdomain.com canonical name = yourdomain.com yourdomain.com refresh = 21600 retry = 7200 expire = 1209600 minimum = 1200

...and there you will be able to see your current Minimum setting in seconds.

If you can't change it, and you are working with high traffic sites and want more control over your DNS you would need to look at using a dedicated DNS provider such as easyDNS. Most (including easyDNS) are registrars aswell, but you don't need to register domains through them, you can just use their DNS-only service, in which case you'd just enter their DNS server addresses when registering a domain name elsewhere.